//^ - y^f SOIL SURVEY OF I.OWA POTTAWATTAMIE COUNTY SOILS AGRICULTURAL EXPERIMENT STATION IOWA STATE COLLEGE OF AGRICULTURE AND MECHANIC ARTS Agfonomy Section Soils Soil Survey Report No. 2 January, 1918 Ames, Iowa OFFICERS AND STAFF IOWA AGRICULTURAL EXPERIMENT STATION Raymond A. Pearson, M. S. A., LL. D., President C. P. Curtiss, M. S. A., D. S., Director W. H. Stevenson, A. B., B. S. A., Vice-Du-ector AGRICULTURAL ENGINEERING C. K. Shedd, B. S. A., B. S. in A. E., Acting Chief W. A. Foster, B. S. in Ed., B. Arch., Assistant J. S. Glass, B. S. in A. E., Assistant AGRONOMY W. H. Stevenson, A. B., B. S. A., Chief H. W. Johnson, B. S., M. S., Assi.stant in Soils H. D. Hughes, B. S., M. S. A., Chief in Farm (absent on leave) Crops George E. Corson, B. S., M. S., Assistant in Soil P. E. Brown, B. S., A. M., Ph. D., Cliief in Soil Survey Chemistrj' and Bacteriologj-. H. W. Warner, B. S., M. S., Soil Survieyor (ab- L. C. Burnett, B. S. A., M. S., Cliief in Cereal sent on leave) Breeding L. L. Rhodes, B. S., Soil Survey (absent on L. W. Forman, B. S. A., M. S., Chief in Field Ex- leave) perinients M. E. Olson, B. S., M. S., Field Experiments John Buchanan, B. S. A., Superintendent of Co- J. F. Bisig, B. 8., Field Experiments operative Experiments O. F. Jensen, B. S., M. S., Assistant in Farm R. S. Potter, A. B., M. S., Ph. D., Assistant Chief Crops (absent on leave) in Soil Chemistry- E. I. Angell, Soil Surveyor R. S. Snyder, B. S., Assistant in Soil Chemistry H. P. Hanson, B. S., Field Experiments (absent on leave) ANIMAL HUSBANDRY W. H. Pew, B. S. A., Chief L. S. Gillette, B. S., M. S., Assistant Chief in J. M. Eward, M. S., Assistant Chief in Animal Dairy Husbandry Husbandry and Chief in Swine Production A. C. McCandJish, M. S. -A., Assistant in Dairy R. Dunn, B. S., Assistant in Animal Husbandry Husbandrj- Orren Lloyd-Jones, M. S., Ph. D., Assistant in Rodney Miller, B. S. A., Assistant in Poultrj- Hus- Animal Husbandry bandry. H. A. Bittenbender, B. S. A., Chief in Poultry Husbandry BACTERIOLOGY R. E. Buchanan, M. S., Ph. D., Chief; Associate in Daii"y and Soil Bacteriology BOTANY L. H. Pammel, B. Agr., M. S., Ph. D., Chief I. E. Melhus, B. S., Ph. D., Chief in Plant Path- Charlotte M. King, Assistant Cliief ology' CHEMISTRY A. W. Dox, B. S. A., A. M., Ph. D., Chief (on A. R. Lamb, B. S., M. S., Assistant leave of absence) S. B. Kuzirian, A. B., A. M., Ph. 1)., Assistant W. G. Gaessler, B. S., Acting Chief G. W. Roark, Jr., B. S., Assistant Lester Yoder, B. S., M. S., Assistant DAIRYING M. Mortensen, B. S. A., Chief I). E. Bailey, M. S., Assistant Chief in Dairying B. W. Hammer, B. S. A., Chief in Dairy Bac- teriology ENTOMOLOGY R. L. Webster, A. B., Chief Wallace Park, B. S., Assistant in Apiculture FARM MANAGEMENT H. B. Munger, B. S., Chief O. G. Lloyd, B. S., M. S., Assistant Chief HORTICULTURE AND FORESTRY S. A. Beach, B. S. A., M. S., Cliief A. T. Erwin, M. S., Chief in Truck Crops T. J. Maney, B. S., Chief in Pomology Rudolph A. Rudnick, B. S., Assistant in Truck Harvey L. Lantz, B. S., Assistant in Fruit Breed- Crops ing G. B. MacDonald, B. S. F., M. F., Chief in For- W. E. Whitehouse, B. S., Assistant in Pomology estry Ajidrew Edward Mumeck, B. A., Research Fellow Frank H. Culley, B. S., M. L. A., Chief in Land- in Pomology scape Architecture J. B. Kendrick, B. A., Research Assistant in Pom- ology RURAL SOCIOLOGY G. H. Von Tungeln, Ph. B., M. A., Chief VETERINARY MEDICINE C. H. Stange, D. V. M., Chief GENERAL OFFICERS F. W. Beckman, Ph. B., Bulletin Editor F. E. Colbum, Photographer Gretta Smith, A. B., Assistant to the Bulletin C. E. Brashear, B. S. A., Assistant to Director Editor SRLF QO URL /44^'V^'^' CONTEXTS Introduction 5 Pottawattamie county's fann crops 6 Pottawattamie county's live stock iiidu^tiy 7 Geologry of Pottawattamie counl >■ 8 Physiography and drainage 9 Soils of Pottawattamie county 11 The different types and their areas 11 The fertility in Pottawattamie county soils 12 The surface soils 12 The subsurface soils and s\ibsoils 15 Greenhouse experiments 16 Field experiment 19 Field experiments with gumbo 22 Needs of Pottawattamie county soils as indicated by clKMiiieaK greenhouse and field tests " " 24 Manuring 24 Commercial fertilizers 26 Lime 27 Drainage 28 Rotation of crops 28 Prevention of erosion 29 Dead furrows 30 Small gullies 30 Large gidlies 33 Bottomlands 33 Hillside erosion 33 Individual soil types in Pottawattamie enuiity 34 Loess soils 34 Tei-raee soils 36 Swamp and bottoiidand soils 39 Appendix : The soil survey of Towa 45 POTTAWATTAMIE COUNTY SOILS By W. H. Stevenson, P. E. Brown, with the assistance of II. P. Hanson and H. W. Reid Pottawattamie county is located in southwestern Iowa along the Missouri river. It is the second largest county in the state, having a total area of 957 square miles, or 612,480 acres. It is entirely wuthin the Missouri loess soil area; 70% of its soils being loessial in origin, while the remaining types fall within the ter- race and swamp and bottomland groups. This county is one of the most important in the state agriculturally, not alone because of its size, but also because of the high normal fertility of its soils and the wonderful adaptation of soil and climatic conditions to the growth of certain valuable crops. Of the total area of Pottawattamie county, 518,784 acres, or 84.7% is in farms numbering 3,101 in all with an average size per farm of 167 acres. The utilization of the farm land is indicated by the folloAving figures, compiled by the state department of agriculture in 1915 : Acreage in pasture 131,000 acres Acreage in farm buildings, feed lots and public highways. . . . 24,639 acres Acreage in orchards 4,962 acres Acreage in gardens : 1,106 acres Acreage in waste land 4,559 acres Acreage in general farm crops 356,050 acres Acreage in crops not otherwise listed 745 acres The type of agriculture is indicated rather definitely in the figures just given and consists in general farming combined to a considerable extent with live- stock raising. The acreage in orchards is not large, but fruit growing is in- creasing rapidly in the county. With the infomiation which is now being se- cured and disseminated regarding the growing and marketing of fruits, or- charding will undoubtedly become of much importance.* Systems of perma- nent fertility adapted to Pottawattamie county should, therefore, include not only general farming, and live stock farming, but also orcharding. The area of waste land in this county is not great but it warrants attention and methods of reclamation or utilization should be devised. Definite advice along this line, of course, can only be given for individual conditions and no general recommendations can be made here. * See Soil Survey of Pottawattamie County, Towa. by A. L. Goodman of the U. S. Depart- ment of Agriculture, and Peter Hanson and Harold W. Eeid of the Iowa Agricultural Ex- periment Station. * An experiment orchard maintained by the Iowa Agricultural Experiment Station near Council Bluffs is yielding much information of value to fruit growers of Pottawattamie and adjoining counties. 6 SOIL SUEVEY OF IOWA TABLE I. ACREAGE, YIELDS AND VALUES OF FARM CROPS IN POTTAWATTA- MIE COUNTY* Acres So total farm jBu. or tons j Total bushels land incountrl per acre | or tons Average price Total value crop Corn 194,000 Oats Spring wheat . Winter wheat. . Barley Rye Potatoes Tame hay. . . . Wild hay. Alfalfa 43,900 10,900 32,000 5,800 500 1,850 34,900 9.700 22,500 Pasture | 131,000 6,402,000 1,404,800 163,500 640,000 162,400 10,000 140,600 59,300 14,500 81,000 0.45 0.32 0.85 0.83 0.51 0.77 0.53 8.94 7.41 11.18 $2,880,900 449,536 138,975 531,200 82,824 7,700 74,518 530,1.42 107,445 905,580 Over three-fifths of the farm land is employed for general farming and the crops grown, in the order of their importance, are com, alfalfa, winter wheat, tame har, oats, spring wheat, wild hay, barley, potatoes, and rA'e. POTTAWATTAMIE COUNTY'S FARM CROPS Corn is particularly adapted to Pottawattamie county and does well on all the soil types, but it is especially suited to the Marshall silt loam where the yields are generally high. On the terrace and swamp and bottomland soils yields are usually lower than on the upland soils, but in favorable seasons quite satisfac- tory crops are obtained. The value of the corn crop is verj^ much greater than that of any of the other crops grown, as will be seen in table I. The ^Missouri loess soil area as a whole is especially suited to the growth of alfalfa and Pottawattamie county stands second among all the counties of Iowa in the production of this crop. Alfalfa grows well on all the soil tjT)es in the county but like com, it does especially well. on the Marshall silt loam. Very few failures to secure satisfactory yields are recorded and three or four cuttings are usually made with jaelds up to seven tons per acre as a common occurrence. The value of alfalfa in this county is second only to com and the acreage is in- creasing each year. Sweet clover is being grown to some extent in place of al- falfa, but its use is not general and it is doubtful if it will ever prove as val- uable as a forage crop. The next crop of importance in this county is wheat. Both winter wheat and spring wheat have been grown, but spring wheat has been quite generally re- placed by the more profitable "v^-inter variety. At the present time the acreage of the latter is three times that of the former. The average yield of the -sAinter wheat is greater than that of the spring variety and the total value to the coun- ty is, therefore, much greater. The tame hay crop in Pottawattamie count}' far exceeds the wild hay in acre- age, yield and value. The tame hay is made up practically entirely of timothy and red clover and its value alone exceeds that of the grain crops, except com and wheat. Oats stand next to corn in acreage and production, but its value is less than that of alfalfa, wheat, and hay. It is a verj- important crop and is found in * Iowa Year Book of Agriculture, 1915. POTTAWATTAMIE COUNTY SOILS 7 nearly all rotations, satisfactory yields being secured in most cases. Practically all the oats produced in Pottawattamie county is fed on the farms. Barley, rye, and potatoes are gro^\Ti to some extent, but the acreage is not large and their value is much less than tliat of the crops already mentioned. The suitability of the land along the ^Missouri river to the production of apples and grapes was recognized by the early settlers. It is only within recent years, however, that these crops have been grown to any considerable extent. The yield of apples in the county in 1915 was 81,942 bushels and the production is constantly increasing. The varieties grown are Ben Davis, Roman Stem, Grimes Golden, Gano,. Jonathan, Winasap, Mammoth Black Twig, and Northwestern Greening. Grape growing has also increa.sed considerably. Over 600 acres are now in vineyards and the yields and profits are quite satisfactory. The dis- posal of the crop is much facilitated thru the aid of cooperative buying and sell- ing associations. Grapes are particularly suited to the Knox silt loam and prove valuable on the steep blutf land near the Missouri river where field crops cannot be gro^^^l satisfactorily. Better methods of handling the \nneyards are quite necessary in many cases and if proper treatment of the soil and vines is followed, this crop can be made one of the most profitable in the county. POTTAWATTAMIE COUNTY LIVE STOCK INT)USTRY The livestock industrj- is well developed in Pottawattamie county. Good market facilities and excellent blue grass pastures render it one of the leading stock raising counties in the state. The extent of this industry is indicated in the following figures compiled in 1915: ^, ^_.^ Horses (all ages) 21, /0.5 Mules (all ages) 2,610 Swine (July 1. 1915) 195,496 Cattle (cows and heifers kept for milk) .... 12,874 Cattle (other cattle not kept for milk) 52,743 Cattle (total, all ages) 71,970 Sheep (all ages on farms) 5,627 Sheep (shipped in for feeding) 7,007 Sheep (total pounds wool clipped) 34,916 The livestock industry' is profitable and should undoubtedly be developed to a much greater extent. Not only are there good returns on the investment made, but the drain on the natural fertility of the soil is less under livestock farming. The value of land in Pottawattamie county is extremely variable. The bot- tom lands along the Missouri river, the least valuable because they are subject to overflow, sell for $65 to $100 per acre. They produce good crops in favor- able seasons. In the eastern three-fourths of the county, where the land is gently rolling to hilly, the prices range from $125 to $250 per acre and here soil and climatic conditions are favorable for the very best crop production. Yields of all crops in Pottawattamie county are good, but experiments show ver}' definitely that they may be increased thru proper methods of management. The soils are not acid except in a few eases and do not generally need lime. Thev are low in organic matter or humus, however, and care should be taken to SOIL SURVEY OF IOWA Fig. 1. Rich alluvial soil on the Missouri river bottoms. Cliaraeteristic loess bluffs in the distance. The alluvial soils are classified in the Wabash soils provide enough of this important material. "With proper treatment and crop- ping, the yields from the soils in this county may be increased to a considerable extent. THE GEOLOGY OF POTTAWATTAMIE COUNTY Pottawattamie county is located in the midst of the Missouri loess soil area bordering on the Missouri river. About three-fourths of the county consists of level to hilly loessial upland and the remaining portion is made up of flat to gently undulating alluvial plains or first bottoms. The rock material underlying the soils of Pottawattamie county represents various geological eras and is of interest technically, but from the agricultural standpoint it is of no importance for it is so deep under the overlying loess that it can have practically no effect on the growth of crops. The whole county was covered by at least one glacier in times past, for evi- dences of glacial deposits are frequently encountered. It is impossible, how- ever, to ascertain whether more than one glacier extended over the county. Resting on this glacial material is a dark-blue to bluish gray or yellow clay known as "bowlder clay," a material undoubtedly of drift origin. It appears only on the steepest slopes where the loess runs out: ordinary slopes show no evidence of it. No great importance from the agricultural standpoint is there- fore attached to the occurrence of this material. With the exception of the steep 1 Udden — Iowa Geo. Survey — Vol. XI, pg. 201. POTTAWATTAMIE COUNTY SOILS 9 slopes mentioned the upland soils everywhere are so deeply covered with loess that the underlying material has practically no influence on the fertility of the soil. The loess is extremely variable, both in color and composition, due of course to the varying conditions under which it has existed. Frequently lime material occurs in considerable amounts. It may be rather uniformly distributed thru the loess but more commonly it is collected into lumps or concretions. These concretions, or ''clay dogs," vary considerably in size and striking accumula- tions are occasionally found along the Missouri river. They are of particular interest in indicating the presence of sufficient lime, or the absence of acidity, in the soil. The loess varies widely in thickness. It is generally much thicker in the western portion of the county and thins out somewhat in the east. The depth may alter within very short distances. The average greatest thickness in the eastern portion of the county is probably 50 feet but it is often less than 40 feet. Along the Missouri river it is usually 70 or 80 feet in thickness and frequently it becomes 150 to 200 feet thick. The loess along the rivers has of course been modified to a considerable ex- tent by the action of the streams in carrying away and depositing material. The terrace soils, or old bottom lands, are therefore distinguished from the loess. The present bottomland soils are likewise considered separately. These three groups of soils constitute the basis for the following discussion and de- scription of the soils of Pottawattamie county. PHYSIOGRAPHY AND DRAINAGE The topography of Pottawattamie county is very uniform, consisting in the main of upland slopes and several flood plains, with some strips of upland plains and a few terraces. The flood plain of the IVIissouri river covers about seven percent of the area. The elevation of this plain is generally less than 20 feet above the average height of water in the river. The flood plains of the "West Nishnabotna and East Nishnabotna rivers are of minor importance, covering comparatively small areas. They are on the average from 100 to 120. feet above the Missouri river. There are also rather large plains or bottomlands formed by numerous smaller streams. The main topographic feature of the county is an old drift plain into which the lowland plains just described have been cut and again partly filled. This plain has a gentle slope to the southwest. The average elevation above sea level is about 1,200 to 1,300 feet. The main streams which cross the country from north to south divide this plain into a succession of broad, parallel swells with a central divide and two gentle slopes doA^-n to the bluffs of the streams. Thus the distinctive, gently undulating to hilly appearance of the loess soil area as a whole is accounted for. The rougher portions of the county, which are found near the bluffs of the Missouri river and consist of numerous narrow ridges and ravines, are undoubt- edly the result of erosion. Thus the topography of some areas has been con- siderably modified thru the action of streams and particularly of creeks. POTTAWATTAMIE COUNTY SOILS 11 The drainage of Pottawattamie county may be said to have a latticed arrange- ment ; the heavy, continuous lines of the main streams run from north-northeast to south-west and the small, more irregular lines of the tributaries run from northwest to southeast. The lines of the secondary streams are separated by areas usually about four-fifths of a mile vdde. In general the drainage system of the county is excellent. The Ea.st Nishna- botna and West Nishnabotna rivers and the various creeks which run in the same direction as these rivers and the tributaries of all these streams provide thoro drainage of the county as a Mhole and artificial drainage is rarely neces- sary. THE SOILS OF POTTAWATTAMIE COUNTY The soils of Pottawattamie county may be grouped into three general classes: the loess soils, the terrace soils, and the swamp and bottomland soils. There are no drift soil areas of sufficient size to be mapped and no residual soils. TABLE II. AREAS OF DIFFERENT GROUPS OF SOILS Acres Per cent 72.7 3.3 24.0 Loess 445,760 Terrace soils 19 648 Swamp and bottomland soils 147 072 Total 612,480 It is apparent from table II that the largest portion of the countj^, almost 75 percent, is covered by the loess soils. There is also a rather large percent of swamp and bottomland in the county. Terrace soils are found only to a small extent. The terrace soils and the swamp and bottomland soils in Pottawattamie coun- ty are uniformly level, but the loess areas are quite variable. The topography of the Marshall silt loam, the most widely distributed loess soil, ranges aU the way from level to hilly, and that of the Knox silt loam varies from level to hilly and in some cases to rough. There are ten distinct soil types in Pottawattamie county, two loess soils, three terrace soils and five swamp and bottom-land soils. Table III shows that the Marshall silt loam is not only the chief loess soil, but TABLE III. TYPES OF POTTAWATTAMIE COUNTY SOILS AND THEIR AREAS Soil No. Types of Soils Acres Percent of total area of county LOESS SOILS 9 Marshall silt loam 416,768 28,992 68 11 Knox silt loam 4.7 TERRACE SOILS 23 Hancock silt loam. . . . 15.744 3,520 384 2 6 24 25 Hancock silty clay. . . . Osgood very fine sand. 0.6 0.1 SWAMP AND BOTTOMLAND SOILS 26 26a 27 28 29 Wabash silt loam Wabash silt loam (coUuvial phase) Wabash silty clay Sarpy very fine sandy loam Sarpy very fine sand 37,184 44,864 51,520 11,008 2,496 13.4 8.4 1.8 0.4 12 SOIL SURVEY OF IOWA it covers by far the largest proportion of the total area of the county, over 68 percent. The other loess soil is of much less importance, covering only 4.7 percent of the total area of the county. The terrace soils are all of minor importance, the total area covered by the three being only 3.3 percent of that in the county. The Hancock silt loam covers the largest area of the three and the Osgood very fine sand is of very small extent, occupying only 0.1 percent of the area of the county. Three of the swamp and bottomland soils are rather extensive in area, the Wabash silt loam, the Wabash silt loam (Colluvial phase), and the Wabash silty clay. The other two types are of minor importance and occupy only a small part of the county. While the loess soils must be considered first in planning systems of soil man- agement for Pottawattamie county, the swamp and bottomlands should not be neglected for they are of considerable extent. Furthermore, these latter soils are much more in need of special treatment to make them profitably productive than the loess soils, altho increases in crop yields on the loess types may also be secured by proper management. All the soil types must be considered, there- fore, in working out systems of permanent fertility for the county. THE FERTILITY IN POTTAWATTAMIE COUNTY SOILS The plant food content of Pottawattamie county soils was determined by analyzing samples of all types found. These samples were secured wdth the usual precautions that they should be true to type and that all variations due to difference in treatment should be eliminated. Three samples were drawn from each of the main soil types and one sample from each of the minor types, just as in the case of the other counties surveyed. Each sample represented the surface soil from to 6% inches deep, the subsurface soil from 6% to 20 inches deep, and the subsoil from 20 to 40 inches deep. Total phosphorus, total nitrogen, organic carbon, inorganic carbon and lime- stone requirement determinations were made on the soils at the three depths ac- cording to the official methods, the Veitch method being employed for determin- ing the limestone requirements THE SURFACE SOILS Table IV presents the results of the analyses of the surface soils, the figures given being the average of duplicate determinations on several samples of each soil in the case of the major types. The results are expressed in pounds per acre of 2,000,000 pounds of surface soil. This table shows wide differences in the plant food content of the various soil types. These variations are noticeable not only when the large soil groups are compared, but also appear among the types within these groups To what ex- tent the latter variations are due to natural differences or to modifications brought about by varying factors cannot be stated. It is certain, however, that loess soils are not necessarily lower or higher in any one constituent than terrace soils or swamp and bottomland soils, and so on. The phosphorus content of the terrace soils in Pottawattamie county is gen- U. S. DEPT. OF AGRICULTURE, BUI Milton Whitney. Chief. Curtis. F. Marbut, SOIL MAP OF POTTAWATTAMIE COirNTY, lOWA-Sfiti TERRACE SOILS DD H '^ SWAMP AND BOTTOMLAND SOILS POTTAWATTAMIE CX)UNTY SOILS 13 erally higher than that of the loess soils or the swamp and bottomland soils. The organic carbon and the nitrogen content of the terrace soils are like\\'ise somewhat greater than in the loess soils, but the differences are not large. The swamp and bottomland soils are on the average lowest in all three constituents. This is unusual as such soils generally contain accumulations of organic matter which lead to the presence of greater amounts of organic carbon, nitrogen and often also of phosphorus. It is evident that in this county these level, low-h-ing soils were originally lower in these elements than the other soils. The content of inorganic carbon, which in a mea.sure shows the lime require- ments of soil, is extremely variable, but it does seem that the swamp and bottom land soils are somewhat higher in this constituent. None of the soils are acid except the Marshall silt loam, but the supply of lime is apparently not extremely high in any of the surface soils. None of the soils in Pottawattamie county are so abundantly supplied with phosphorus that this element can be disregarded in systems of soil improvement and permanent fertility. There is enough phosphoiiis in all the soils for sev- eral crops if it is made available rapidly enough, but when the total phosphorus present is not abundant the rate at which it is made available is certain to be very low. It is doubtful, therefore, if sufficient prosphorus would be made avail- able to keep crops properly supplied for any considerable length of time. In fact, in the case of some of the soil types applications of phosphorus might be of value at the present time. This point will be considered further in connection with the greenhouse experiment on the Marshall silt loam. In general phos- phorus must be considered in all systems of fertility which are devised for the soils of this county. The nitrogen supply is low in practically all Pottawattamie county soils. Only in the case of the Hancock silty clay is there anything like a fair amount of this constituent. The swamp and bottomland soils are notably low in nitro- gen, a rather unusual state of affairs as has already been pointed out. The organic carbon content of the various soils is correspondingly low as is apt to TABLE IV. PLANT FOOD IX POTTAWATTAMIE COUNTY SOILS. IOWA POUNDS PER ACRE OF TWO MILLION POUNDS OF SURFACE SOIL (0-6-%") Soil No. Soil Type Total phos- phorus Total nitrogen Total organic carbon Total inorganic- carbon Lime- stone require- ment LOESS SOILS 9 11 Marshall silt loam Knox silt loam 1313 1200 3260 1710 37,S07 16.065 146 4355 1779 Basio TERRACE SOILS 23 24 25 Hancock sUt loam Hancock silty clay Osgood very fine sand 1500 1900 1220 2860 4380 1340 34,104 52,428 10.670 2516 132 3070 Basic Basic Basic SWAMP AND BOTTOMLAND SOILS 26 26a 27 28 29 Wabash sUt loam Wabash silt loam (Colluvial phase) Wabash sUty clay Sarpy very fine sandy loam Sarpy very fine sand 1360 2820 1360 2960 1380 1740 1020 1780 840 440 38,928 36,726 22,644 15,710 10,300 1042 394 7236 4230 3900 Basic Basic Basic Basic Basic 14 SOIL SURVKY OF IOWA be the case, the swamp ami bottonihiiul soils beiiii;- particularly deficient in this constituent for soils of such a nature. All of the soils are low in orjjanic nuitter. That is evident because the nitro- gen and organic carl)on occur in such relatively small amounts in practically all cases. Farm manure should be applied in as large amounts as practicable and green manure crops, preferably legumes, should be turned under in order to bring these soils up to a proper content of organic matter, and to insure the best mechanical and chemical soil conditions for the growth of bacteria and the pro- duction of available plant food. The relation between the carbon and nitrogen in some of these soils is such that there is not the best bacterial action or the best decomposition of the organic matter. In some instances, therefore, the need of organic uuitter which will undergo rapid decomposition is very clearly shown. The greatest immediate need of the soils in Pottawattamie county is evidently for organic matter and steps should be taken to supply an abundance of fresh, easily decomposable material. Rotations should include a legume and a green manure "catch crop." Crop residues should be completely utilized and the farm manures should be preserved carefully and applied in as large quantities as available, if permanent fertility is to be maintained. The inorganic carbon content of Pottawattamie soils is comparatively high. In a general way the swamp and bottomland soils are highest in this constituent. The abundance of inorganic carbon, reflecting as it does the lime content of the soil, indicates that the soils are not likely to be acid in reaction. This is the case. Only one soil type shows any limestone reiiuirement whatever and the amount needed there is small. Of the three samples of the Marshall silt loam two showed slight aciditv and one was basic. The average result given in Fii A loess Iduff. Erosion is very nctivo on tlirsc ill tlie loess liills iiiiil carves fantastic sliapes U. S. DEPT. OF AGRICULTURE, BURE Milton Whitney, Chief. Curtis. F. Marbut. in WAS HmO Douo; SOIL MAP OK POTTAAVATTAMIE ('OIXTY, lOWA-Seclion II. SWAMP AND BOTTOMLAND SOILS # POTTAWATTAMIE COUNTY SOILS 15 table IV for tliis soil type shows, therefore, a small limestone re(iuirement. All the other soil types were distinctly basic in reaction. It is apparent that the need for applications of lime is restricted to special cases. Since the chief soil type in the county is occasionally found to be slightly acid and therefore in need of lime, the soils in this county should always be tested for acidity. • As a whole Pottawattamie county .soils are particularly deficient in organic matter and nitrogen as well as phasphorus may be the limiting factor of crop pro- duction in the near or more or less distant future. Occasionally Pottawattamie soils may be acid and in need of lime. Applications of humus fonning mate- rials, of phosphorus and of lime may be necessary in many cases and tests of the value of such materials should be made. THE SUBSURFACE SOILS AND SUBSOILS The results of the analyses of subsurface soil, and subsoil samples were cal- culated as pounds per acre of 4,000.000 pounds of subsurface soil and of 6,000,- 000 pounds of subsoil. The results are given in tables V and VI. TABLE V. PLANT FOOD IN POTTAWATTAMIE COUNTY SOILS, IOWA POUNDS PER ACRE OF FOUR MILLION POUNDS OF SUBSURFACE SOIL (6-%-20") Soil No. Soil Type- Total phos- phorus Total nitrogen Total organic carbon Total norganic carbon Lime- stone require- ment LOESS SOILS 9 11 Marshall silt loam Knox silt loam 1 2600 1 2340 5733 1840 55,914 17,838 298 14,282 1223 Basic TERRACE SOILS 23 24 25 1 Hancock silt loam Hancock silty clay Osgood very fine sand 1 2800 3120 1960 2840 6800 1360 28,312 73.016 6,240 24,008 264 15,000 Basic Basic Basic SWAMP AND BOTTOMLAND SOILS 26 Wabash silt loam 2600 5520 52,396 2964 Basic 26a Wabash silt loam (Colluvial phase) 3040 6520 77,112 968 Basic 27 Wabash silty clay 2760 3880 71,416 17,824 Basic 28 Sarpy very fine sandy loam 2000 2520 25.560 8,600 Basic 29 Sarpy very fine sand 1560 560 13,304 8,136 Basic TABLE VI. PLANT FOOD IN POTTAWATTAMIE (X)UNTY SOILS. IOWA POUNDS PER ACRE OF SIX MILLION POUNDS OF SUBSOIL (20"-40") Soil No. Soil Type Total phos- phorus Total nitrogen Total organic carbon Total inorganic carljon Lime- stone rt'(|uire- ment LOESS SOILS 9 11 Marshall silt loam Kno.x silt loam 3700 3330 5080 2070 65,590 12,909 9,230 22.761 Basic Basic TERRACE SOILS 23 I Hancock silt loam 24 I Hancock silty clay 25 Osgood very fine sand 26 26a 27 28 29 3900 4260 3300 2100 6600 1200 65,844 63,834 12,640 43,596 426 22.860 SWAMP AND BOTTOMLAND SOILS Wabash silt loam Wabash silt loam (Colluvial phase) Wabash silty clay Sarjiy very fine sandy loam Sarj)y very fine sand 3960 5280 3660 2700 2520 7980 11280 4380 2160 420 54,474 146.628 40,578 21.774 22.050 1,746 606 31,962 23,706 11.790 Basic Basic Basic Basic Basic Basic Basic Basic Id Hon. HIIU.Vi:V OK IOWA Nn llll'Kf MIIMMIIiIm (iT IIIIV III' ihr iKTCSHIiry |illilll IntMl (mmimI il lirlild lire prcHrlll, III llif luwcr Hoil liiyci'M willi llii" f\cr|il nm ol' imtrjfimic ('(iilinn. 'Tlic hiihiiihI of lliH rlniM'iil. in nillior liii'Kr in nmhh' niNCH nml mdirfilcH llic iiIinciicc ol' iickI Noil ol' Ilic MiiihIuiII Mill louni mIiowm h niiiiiII liiiir rninircincnl,. Nono of Mie ollirr MiiltMnfrin'o Noilw sliow iiny nctMJ Tor liiiir. In Ilir cmho of (.lir hmU SoilN. notU' of llio MiiinplcM \Vi'n< lii-nj II im rviilriil, llirnnl^ of llll^S(< wns conilMcli'il in • !HM) iinil llii^ ollirr wiin oirnrd on m.m pnrl ol' llir soil Mnrvey in l!>l I l;». In llir IIi'mI i^sprriiiicnl. Irii polM worr nsnl, tlii^ I n'iiiin wci^lils oMninnl iim iimiiiI. 'I'lir nvsnlls ol' llio oxporiiiii'iil hit ^••ivon in liiMr \' 1 1 'I'lir limo luid no rlVrcl on llir crop ^-'own Wlirii lilllo>.^rn WllM (iddrd uilli llir llllu^ llirrr wmm un iiirrrjiMo in llir crop riio',pli(Miis, iilvrwisr. Iiroindd nhonl. l''lH. I, tiUH'ulum.'U' i\|riup,i,l \,. ■ lliiinillnii' ulnil I'n'r'l'AWA'r'I'AMIK OnllNTV Mn||,M IT 'rAIII,!'; VII OUMKNIUHIHK I'lM'MIM M I'iN'l". IIHiil MAMMIIAI.I, Mil,'!' MiAM I'll), Nfi. 'riniiliiinil III (II I( IM I. lino li;i liliiMt I NlliiiHon (I'i llllllK I I'ImiII||||IIHIN Wt lilino I I'lilMMrilnin (1(1 lillMII I Nlllll^KII I |'lllin|llllll MH (17 liliiiii I Nllrii(ji/nlli('r willi IIm' liliM' ilici'riiMcd llir »'r|ili<'d l>i lln' miiiii WHJ lype in l'oll/iwiill»imie eonnly. Lime liiid no ell'i-el Nilrof/in mid plioM|ihoniN iincli hnniKhl. (iImhiI. ii nolieenhle inereiiNe in erop yield When nilio (^en mid phoMphorni were employed lo(o|||cr, Ihe tl)'if\ w/iu f/renP'r llimi lliiil produced hy e;ieh (done The Hceond ex|)erimenl, eondiielnl m IIm' i/recnliooni' in I'M I |!*, involved Ihe more priielieni IchIh of Ihe iipplie/dion oi' mmiiiie mid of phoNphoriin in Ihe iiviiil (ihle or (leid plioM|ihiile jorm mid in Ihe roel( phoHplnile or iiiholnhle form hime wiiH iipplied in Niirijeietd iimoiinl lo niid riili/,e Ihe (teidily iind supply I wo Ioiih midilion/il ; mminivt wuh iiHed u\ Ihe rule (d' M) lonn per nere ; tieid phoMphnle nl, f,lie rule ol* 'MH) ponndN per nere, /md roelt phoHphnle nl Ihe rule ol' l,0(K) poiimU jwr iicre. Tim niHiillx ol' Ihin experiment, nre, jriven in Inhle VIII, Ihe iiverni/n (\vy weii/hl in >/''""•*< 'd' Ihe wlieni ero|» from Ihe diiplieiile pol« heinj/ recorded, An exnminnlion fine crumbly surface soil prevented this cracking. On the hard, cracked ground the corn turned yellow and "fired" about the middle of August, but on the other plots it re- mained green at least three weeks longer. The fall plowed plots were fairly clean of weeds and grass while the others were very foul. The lime treatment of plot 105 seemed to have no effect on the "gumbo." This experiment shows very definitely • the possibilities of "gumbo" soils .when properly drained and fall plowed. The drainage of "gumbo" is more readily accomplished than would be supposed. On the upland the tile should be laid 8 rods apart to secure good drainage, altho reports have been made of successfully drained "gumbo" when the tile was 10 to 12 rods apart. On the lowland "gumbo" the tile should be somewhat closer together, but the securing 24 SOIL SUEVEY OF IOWA of a satisfactory outlet is the chief necessity for thoro drainage and in some eases it may be necessary to run an open ditch thru to the river, in wihich case a drainage district must be organized. Wlien properly tiled out such ''gumbo" soil is equal to any other soil in the state in producing power for general farm crops. Fall plowing improves the soil very decidedly and the use of clover or some other green manure is also of value. Lime apparently is of no use on such soils. The occurrence of "gumbo" on a farm need not be a cause of lower value of the farm. It may be made and kept productive thru the treatments men- tioned above and is then equal in value to the best farm land. THE NEEDS OF POTTAWATTAMIE COUNTY SOILS INDI- GATED BY CHEMICAL, GREENHOUSE AND FIELD TESTS MANURING The value of a sufficient amount of organic matter in soils is well known. Commercial plant food materials alone are quite insufficient to keep a soil in the proper condition for satisfactory growth. The physical conditions soon become unfavorable, bacterial action is restricted and the plant food present in the soil largely remains in its normally useless condition if the organic matter or humus content of the soil becomes low. The soils of Pottawattamie county are noticeably deficient in organic matter even in the case of swamp and bottomland soils, which is unusual. Potta- wattamie soils are so open and thoroly aerated that the decomposition of organic matter proceeds at a veiy rapid rate. The accumulation of organic matter from plant residues is, therefore, very slow, if any increase at all occurs. In fact, in a great majority of cases there has been a gradual loss of humus, the removal of organic matter by decomposition having proceeded faster than the addition of material thru the ordinary methods of cropping which are followed. Furthermore, with this rapid removal of organic matter there has been a con- tinual loss of plant food thru the production of greater amounts of available food than necessary for the crops grown. If the loess soils had not been espe- cially well supplied with plant food origiually, still greater deficiencies in cer- tain constituents would be found now. These soils were once evidently very rich in plant food, especially in lime, and hence in spite of the large losses, their supply of food constituents is not generally depleted to a danger point. How- ever, if steps are not taken in the near future to check the heavy losses that are going on the time will soon come when extreme measures will be necessary to make the soils profitably productive. Better methods of management than are at present followed will not only prevent the wearing out of the soils, but will also make them more productive immediately. The laboratory, greenhouse and field tests show beyond doubt that organic matter should be used on these soils to increase their fertility and keep them fertile. Organic matter may be added in the form of farm manure, green manures and crop residues and all three should be used. POTTAWATTAMIE COUNTY SOILS 25 Crop residues, consisting of the straw, stover, roots and stubble of crops, add considerable organic matter or humus and also return much plant food to the soil. Under ordinary farming conditions roots and stubble remain in the soil. Too often, however, the straw, and stover are not returned. Nothing should interfere with the return of these materials. On the livestock farm they should be utilized for feed and bedding and returned in the manure and on the grain farm they should be even more carefully used, because the manure which has additional value is not available. The "life" of a soil, or the time during which it will remain productive, is much longer where the crop residues are carefully utilized. Crop residues alone are insufficient, however, to keep up the organic matter supply in soils. This fact is especially noticeable in the loess soils, such as are found in Pottawattamie County, Farm manures and green manures must be used in addition. Farm manure supplies a large amount of organic matter and considerable plant food and besides it adds enormous numbers of bacteria. These organisms are responsible for decomposition processes and hence bring about the produc- tion of available plant food in the soil. The value of farm manure on the Marshall silt loam, the main soil type in Pottawattamie county, has been well shown by the greenhouse and field results referred to earlier in this report. No other material apparently can take its place in increasing crop production. The experiment with the rather infertile hill top soil showed especially the great value of manure in making this soil more productive.. Other fertilizing materials, while of some value, had com- paratively small effects. All the manure produced on the livestock farm, should, therefore, be added to the soils. Furthermore, the manure should be very care- fully stored while awaiting use. Great losses may occur thru improper storage and the more readily available and valuable plant food may disappear almost entirely. As much as 85% of the valuable matter in manure may be lost thru careless handling. The ordinary application of 10 tons of manure to the soil once in the four-year rotation is not sufficient to keep soils fertile indefinitely. The soils of Pottawattamie county, and particularly the Marshall silt loam, should receive heavier applications at the present time to improve their physical condition and make them more productive. Too large amounts are not likely to be applied because of the lack of material, but 16 to 20 tons per acre should not be exceeded. On livestock farms manure may often be applied as recommended, but on grain farms green manure crops must be used in place of manure. Further- more, farm manure is not alone sufficient to keep the soil fertile and green ma- nures also have a place on livestock farms. Green manure crops are so varied that they may be employed under almost any conditions. Legumes are par- ticularly valuable because when well inoculated, as they should be, they take nitrogen from the air and thru their use the nitrogen content of the soil may be increased. At the same time such crops supply organic matter as well as do non- legumes. There can be no question of the value of such green manures on the soils of 26 SOIL SURVEY OF IOWA Pottawattamie county. The experiment reported hardly gives a fair evidence of their value, inasmuch as the cowpeJi crop was so small. Tlu'v should be used in addition to farm manures, either by introduction into the rotatiim as "catch" crops or by turning under a full season's crop. The relative merits of farm manures and green manures need not be considered here, for both are valuable and the latter should be regarded as supplementing or taking the place of the former. It is often advisable to make a small application of farm ma- un ic jilong with a green manure crop to start the necessary decomposition. There are some dangers in the use of green manures, chiefly in the reduction of soil moisture, which may occur in turning under a large crop. In dry sea- sons the time for turning under a green manure crop should be carefully chosen to avoid any injurious action. The crop should be green and full of moisture, for it decomposes more rapidly under those conditions, and it should be plowed under before the soil is cool. Both green manures and farm manures should 1 1' us((l with care and common sense and then there will be no danger in their employment. In choosing the crop for a green manure, select one which will be suitable for the particular soil and climatic conditions and which will not interfere with the regular rotation. The cost of seeding and the monetary value of the crop for hay or pasture should also be considered. Acid conditions in the soil are increased by the use of all materials furnish- ing organic matter and the lime content of the soil must be carefully looked after if farm manure or green manures are employed. COMMERCIAL FERTILIZERS Pottawattamie county soils do not have an abundance of nitrogen or phos- phorus and hence it might be assumed that applications of commercial fer- tilizers might prove profitable. The greenhouse and field experiments show, however, that such materials do not give large increases in crop yields. Nitrogen should not be applied as a commercial fertilizer as long as it is possible to keep up the supply by the use of leguminous green manure crops. Connnercial nitrogenous materials should be used on Iowa- soils only in special ca.ses where a certain crop needs an initial stimulus or where experiments have shown them to be profitable. Leguminous green manures are cheaper and have the additional value of maintaining the organic matter supply in the soil. Phosphorus is not abundant in Pottawattamie county soils, but while appli- cations of phosphates bring about some gains, they do not always give suffi- cient crop increases to warrant their use. Compared with the use of manure, the use of phosphorus is of small value. When added with manure it brings about only small gains. Altho the amount of phosphorus is low in loess soils, when organic matter or humus is snpi)lied and the soil bacteria are active, enough phosphorus becomes available in the soil to supply crop needs and at present additions of phosphorus do not increase yields to any large extent. The amount of phosphorus in some of the other soils of the county is less than that in the Marshall silt loam and on such soils the effects of phosphorus fertilizers might be greater. While farm yard manure returns some of the phosphorus removed from soils POTTAWATTAMIE COUNTY SOILS 27 by crops, the amount available on the average farm is entirely too small to keep up the supply of phosphorus. Sooner or later commercial phosphorus fer- tilizers will be necessary. Unfortunately the experiments thus far carried out on the loess soils do not show definitely which form of phosphorus fertilizer should be emi)loyed. Bone meal was used in tht^ field lest and the results showed an increase, but bone meal cannot be recommended because of the diffi- culty in obtaining it. That leaves a choice between the insoluble rock phos- phate and the soluble acid phosphate. The greenhouse experiment showed slight gains from acid phosphate while the rock phosphate for some unknown reason depressed the yield. This must be regarded as an accidental result and hence no comparison of the two materials is possible at the present time and no rec- ommendation of one over the other can he made. Field experiments carried out under a wide variety of soil conditions are necessary in order to reach defi- nite conclusions. Fanners are urged to test both materials under ordinary farming conditions. Complete directions for such tests and advice for specific conditions will be given by the Soils Section upon application by farmers. No analyses for potassium were made of Pottawattamie county soils for this element is so abundant in all the soils of the state that it hardly seemed necessary. In the field experiment with the hill top soil a few tests were made with potas- sium, and while a slight gain was secured in one ease, in general the effect was practically negligible. It is evidently true that potassium fertilizers are un- necessary on the soils of Pottawattamie county at the present time. Only where special crops need stimulation during the early stages of their growth should potassium salts be applied. It is apparent that the maintenance of the permanent fertility of Potta- wattamie soils does not require the application of complete commercial fertiliz- ers. Potassium is not necessary and will not be needed for a long time. Nitro- gen is low, but this can be more cheaply and better supplied in leguminous green manure crops than in commercial nitrogenous fertilizers. Phosphorus is the . only element which must be supplied in a commercial form. The amount pres- ent is so small that evidently means must soon be taken to replenish the supply. Just what form of phosphorus fertilizer to employ cannot be definitely stated now and neither can the value of its use at the present time be given. LIME The soils in Pottawattamie county are generally well supplied with lime, but some types are low in lime and therefore need applications of this material from time to time to keep them from becoming acid. For example, the Marshall silt loam is occasionally acid. All of the soils in this county should be carefully tested for acidity, and especially the upland loess and hill top soils. The appli- cation of other necessary fertilizei's will be practically useless if lime is lacking in the soils. The use of organic matter, which has been shown to bring about such striking increases in yields, would not prove as valuable in the absence of lime. Furthermore, those soil types which are apparently well supplied with lime at the present time will gradually lose it. The use of organic matter will increase the production of acids which will in turn cause the rapid disappear- ance of lime. Whenever the crop producing power of a soil rich in lime is 28 SOIL SURVEY OF IOWA increased by proper methods of treatment, lime is rapidly removed and must be supplied eventually. If tests show a soil to be acid, three to four tons of lime will supply all that is necessary for several years on practically any soil in Pottawattamie county. This amount will neutralize all the acidity and leave two tons additional in the soil. Such an amount applied in a four-year rotation will keep the soil in the proper condition for crop gro'«i;h as far as acidity is concerned. However, the very best results are always secured by testing each soil and applying the amount which the soil is found to need. DRAINAGE Practically all the soils in Pottawattamie county are well drained. In fact, most of them are too thoroly drained. They are so open, and so well aerated that the organic matter content has been rapidly decreased and valuable plant food has been lost. In general, therefore, there is more need in this county for the adoption of methods of retaining moisture in the soils than of providing drainage. There are two soil types, however, the Hancock silt loam, a terrace soil, and the "Wabash silty clay, a bottomland soil, which show the need of drainage in their level portions. The poorly drained areas of these types are small and hence drainage cannot be considered of great importance in the county. But whenever it is necessary, an efficient drainage system should be installed. No amount of fertilization, care or treatment of any kind will offset the injurious effect of poor drainage. ROTATION OF CROPS For the continued fertility of any soil, a well defined crop rotation should be followed. The continuous growing of any one crop seems to deplete the soil very rapidly and to reduce crop production. Whatever rotation of crops is used, legumes should be included and green manure crops, crop residues and farm manure should be carefully employed to build up and keep up the organic matter in the soil. Definite rotations are difficult to suggest, owing to the ^vide range of conditions which must be met, but the following would serve quite satisfactorily in many eases: 1. FOUR OR FIVE-YEAR ROTATION First year: Corn (with cowpeas, rape, or rye seeded in the standing corn at the last cultiva- tion). Second year: Corn. Third year: Oats (with clover or with clover and timothy). Fourth year: Clover. (If timothy was seeded with the clover, the preceding year, the rota- tion may be extended to five years. The last crop will consist principally of timothy). 2. FOUR- YEAR ROTATION WITH ALFALFA First year: Corn. Second year: Oats. Third year: Clover. Fourth year: Wheat. Fifth year: Alfalfa. (This crop may remain on the land five years. This field should then be used for the four-year rotation outlined above). 3. THREE-YEAR ROTATION First year: Corn. Second year: Oats or wheat (with clover seeded in the grain). Third year: Clover. (Only the grain and clover seed should be sold; in grain farming most of the crop residues, such as corn stover and straw should be plowed under. The clover may be clipped and left on the land to be returned to the soil). POTTAWATTAMIE COUNTY SOILS 29 In livestock fanning the products grown in the rotation should, for the most part 'be fed or used for bedding and the manure carefully saved and used as a fertilizer. "Catch" crops, such as cowpeas, soybeans, vetch and clover seeded in stand- ing com, are frequently unprofitable in Iowa because of the high cost of the seed and the failure of the crop to make a satisfactory growth. The non- legumes, such as rye and rape, usually do well when seeded in standing com. THE PREVENTION OF EROSION Erosion is the carrying away of soil thru the free movement of water over the surface of the land. If all the rain falling on the ground were absorbed, erosion could not occur, hence it is evident that the amount and distribution of rainfall, the character of the soil, the topography or the "lay of the land," and the cropping of the soil are the factors which determine the occurrence of this injurious action. Slowly falling rain may be very largely absorbed by the soil, provided it is not already saturated with water, while the same amount of rain in one storm will wash the soil badly. When the soil is thoroly wet, the rain falling on it will of course wash over it and much soil may be carried away in this manner. Light, open soils which absorb water readily are not apt to be subject to ero- sion while heavy soils such as loams, silt loams and clays may suffer much from heavy or long-continued rains. Loess soils are very apt to be injured by erosion when the topography is hilly or rough and it is this group of soils which is affected to the greatest extent in Iowa. Flat land is, of course, little influenced by erosion. Cultivated fields or bare bluffs and hillsides are especially suited for erosion while land in sod is not affected. The character of the cropping of the soil may therefore determine the occurrence of the injurious action. The careless management of land is quite generally the cause of the erosion in Iowa. In the first place, the direction of plowing should be such that the dead furrows run at right angles to the slope; or if that is impracticable, the dead furrows should be "plowed in" or across in such a manner as to block them. Fall plow- ing is to be recommended whenever possible as a means of preventing erosion. Only when the soil is clayey and absorption of water is very slow will spring plowing be advisable. The organic matter content of soils should be kept up by the addition of farm manures, green manures and crop residues if soil subject to erosion is to be properly protected. By the use of such materials the absorb- ing power of the soil is increased and they also bind the soil particles together and prevent their washing away as rapidly as might otherwise be the case. By all these treatments the danger of erosion is considerably reduced and expensive methods of control may be rendered unnecessary. There are two types of erosion, sheet washing and gullying. The former may occur over a rather large area and the surface soil may be removed to such a large extent that the subsoil will be exposed and crop growth prevented. Sheet washing often occurs so slowly that the farmer is not aware of the gradual re- moval of fertility from his soil until it has actually resulted in lower crop yields. Gullying is more striking in appearance but it is less harmful and it is usually more easily controlled. If, however, a rapidly widening gully is allowed to 30 SOIL SURVEY OF IOWA grow unchecked an entire field may soon be made useless for farming purposes. Fields may be cut up into several portions and the farming of such tracts is more costly and inconvenient. In Pottawattamie county gullying occurs to an injurious extent mainly in the bluffs along the Missouri River and a helt one- half mile to three miles back from the bluffs. The means which may be employed to control or prevent eiosion in Towa may be considered under five headings a.s applicable to "dead furrows," to small gullies, to large gullies, to bottoms, and to hillside erosion. EROSION DUE TO DEAD FURROWS Dead furrows or back furrows, when mnning with the slope or at a consider- able angle with it, frequently result in the formation of gullies. ^'Plowing In/' — It is (piite customary to "plow in" the small gullies that result from these dead furrows and in level areas where the soil is deep, this "plowing in" process may be quite effective. In the more rolling areas, how- ever, where the soil is rather shalloAv, the gullies formed from dead furrows may not be entirely filled up by "plowing in." Then it is best to supplement the ' ' plowing in ' ' with a series of ' ' staked in ' ' dams or earth dams. "Staking In." — The method of "staking in" is better as it requires less work and there is less danger of washing out. The process consists in driving in several series of stakes across the gully and up the entire hillside at intervals of from 15 to 50 yards, according to the slope. The stakes in each series should be placed three to four inches apart and the tops of the stakes should extend well above the surrounding land. It is then usually advisable to weave some brush about the stakes, allowing the tops of the brush to point up-stream. Additional brush may also be placed above the stakes, with the tops pointing up- stream, peniiitting the water to filter thru, but holding the fine soil. Earth Dams. — Earth dams consist of mounds of soil placed at intervals along the slope. They are made somewhat higher than the surrounding land and act in much the same way as the stakes used in the "staking in" operation. There are some objections to the use of earth dams, but in many cases they may be quite effective in preventing erosion in "dead furrows." SMALL GULLIES Gullies result from the enlargement of surface drainageways and they may occur in cultivated land, on steep hillsides in grass or other vegetation, in the bottomlands, or at any place where water runs over the surface of the land. Small gullies may be filled in a number of ways but it is not practicable to fill them by dumping soil into them, for an immense amount of labor is involved and the effect will not be permanent. "Staking in." — The simplest method of controlling small or moderate sized gullies and the one that gives the most general satisfaction is the "staking in" operation recommended for the control of dead furrow gullies. The stakes should vary in size with the size of the gully, as should also the size and quantity of brush w'oven about the stakes. A modification of the system of "staking in" which has been used with success in one case consists in using the brush without stakes. The brush is cut so that a heavy branch i)ointing downward, is left POTTAWATTAMIE COUNTY SOILS 31 Fig. 6. Erosion in gully near the top. This heavy branch is caught between a fork in the lowor part nf the brush-pile, or hooked over one of the main stems and driven well into the ground. Enough brush is placed in this manner to extend entirely across the gully, with the tops pointed downstream instead of upstream, which keeps it from being washed away as readily by the action of a large volume of water flowirig vipon it. A series of these brushpiles may be installed up the course of the gully and with the regular repair of washouts or undereuttings may prove very effective. The Straw Dam. — A simple method of preventing erosion in small gullies is to fill them with straw. This may be done at threshing time with some saving of time and labor. The straw is usually piled near the lower part of the gully, but if the gully is rather long or branching, it should be ])laced near the middle or below the junction of the branches or more than one dam should be used. The pile should be made so large that it will not wash out readily when it gets smaller thru decomposition and settling. One great objection to he use of straw is the loss of it as a feed, as a bedding material and as a fertilizer. Yet its use may be warranted on large farms which are o])erate(l on an extensive scale be- cause of the saving in time, labor and inspection. The Earth Dam. — The use of an earth dam or mound of earth across a gully may be a satisfactory method of controlling erosion under some conditions. It will prove neither efficient nor permanent, however, unless the soil above the dam is sufficiently open and porous to allow of a rather rapid removal of water by di'ain- age thru the soil. Otherwise too large amounts of water may accumulate above the dam and wash it out. In general it may be said that when not provided 32 SOIL SUEVEY OF IOWA with a suitable outlet under the dam for surplus water the earth dam cannot be recommended. When such an outlet is provided the dam is called a ' ' Chris- topher" or "Dickey" dam. The "Christopher" or "Dickey" Dam. — This modification of the earth dam consists merely in laying a line of tile down the gully and beneath the dam, an elbow or a "T" being inserted in the tile just above the dam. This "T," called the surface inlet, usually extends two or three feet above the bottom of the gully. A large sized tile should be used in order to provide for flood waters and the dam should be provided with a cement or board spillway or runoff to prevent any cutting back by the water flowing from the tile. The earth dam should be made somewhat higher and -VN^der than the gully and higher in the center than at the sides to reduce the dangers of washing. It is advisable to grow some crop upon it, such as sorghum, or even oats or rye, and later seed it to grass. Considering the cost, maintenance, permanence, and efficiency, the Christopher or Dickey dam, especially when arranged in series of two or more, may be regarded as the best method of filling ditches and gullies and as especially adapted to the larger gullies. The stone or nibble dam. — ^Where stones abound they are frequently used in constructing dams for the control of erosion. "With proper care in making such dams the results in siiiall gullies may be quite satisfactory, especially when tile openings have been provided in the dam at various heights. The efficiency of the stone dam depends rather definitely upon the method of construction. If it is laid up too loosely, its efficiency is reduced and it may be washed out. Such dams can be used only very infrequently in Iowa. The rubbish dam. — The use of rubbish in controlling erosion is a method sometimes followed and a great variety of materials may be employed. The results are in the main rather unsatisfactory and it is a very unsightly method. Little effect in. preventing erosion results from the careless use of rubbish even if a sufficient amount is used to fill the cut. The rubbish dam may be used, however, when combined "svith the Dickey system, just as the earth dam or stone dam, provided it is made sufficiently compact to retain sediment and to withstand the washing effect of the water. The ivoven wire dam. — The use of woven-wire, especially in connection with brush or*rubbish, has sometimes proven satisfactory for preventing erosion in small gullies. The woven wire takes the plaae of the stakes, the principle of construction being otherwise the same as in the "staking in" system. It can only be reconmiended for shallow, fiat ditches and in general other methods are somewhat preferable. Sod strips. — The use of narrow strips of sod along natural surface drainage- ways may often prevent these channels from washing into gullies, as the sod serves to hold the soil in place. The amount of land lost from cultivation in this way is relatively small as the strips are usually only a rod or two in width. Bluegra&s is the best crop to use for the sod, but timothy, redtop, clover or alfalfa may serve quite as well and for quick results sorghum may be employed if it is planted thickly. This method of controlling erosion is in common use in certain areas and it might be employed to advantage in many other cases. The concrete dam. — One of the most effective means of controlling erosion is by POTTAWATTAMIE COUNTY SOILS 33 the concrete dam, provided the Dickey system is used in connection with it. They are, however, rather expensive. Then, too, they may overturn if not properly designed and the services of an expert engineer are required to insure a correct design. Owing to their high cost and the difficulty involved in secur- ing a correct design and construction, such dams cannot be considered as adapted to general use on the farm. Drainage. — The ready removal of excess water may be accomplished by a system of tile drainage properly installed. This removal of water to the depth of the tile increases the water absorbing power of the soil, and thus decreases the tendency toward erosion. Catch wells properly located over the surface and consisting of depressions or holes filled with coarse gravel and connected with the tile help to catch and carry away the excess water. In some places tiling alone may be sufficient to control erasion, but generally other means are also required. LAEGE GULLIES The erosion in large gullies which are often called ravines may in general be controlled by the same methods as in the case of small gullies. The Christopher dam, already described, may also serve in the case of large gullies. The pre- cautions to be observed in the use of this method of control have already been described and emphasis need only be placed here upon the importance of carrj'- ing the tile some distance down the gully to protect it from washing. The Dickey dam is the only method that can be recommended for controlling and filling large gullies and it seems to be giving very satisfactory results at the present time. BOTTOMLANDS Erosion frequently occurs in bottomlands and especially where such low- lying areas are crossed by small streams the land may be very badly cut up and rendered almost entirely valueless for farming purposes. Straightening and tiling. — The straightening of the larger streams in bottom land areas may be accomplished by any community and while the cost is con- siderable, large areas of land may thus be reclaimed. In the case of small streams, tiling may be the only method necessary for reclaiming useless bottom land and it often proves very efficient. Trees. — Erosion is sometimes controlled hy rows of such trees as willows which extend up the drainage channels. While the method has some good features it is not generally desirable. The row of trees often extends much further into cultivated areas than is necessary and tillage operations are inter- fered with. Furthermore, the trees may seriously injure the crops in their im- mediate vicinity because of their shade and because of the water which they remove from the soil. In general it may be said that in pastures, bottomlands and gulches the presence of trees may be quite effective in controlling erosion, but a row of trees across cultivated land or even extending out into it, cannot be recommended. HILLSIDE EROSION Hillside erosion may be controlled by certain methods of soil treatment which are of value, not only in preventing the injurious washing of soils, but in aiding materially in securing satisfactory crop growth. 34 SOIL SURVEY OF IOWA Use of organic mottrr. — Organic matter or Iniiuus is the most effective means of increasing the absorbing power of the soil and hence it proves very effective in preventing erosion. Farm manure may be used for this purpose or green manures may be employed if farm manure is not available in sufficient 'amounts. Crop residues such as straw, corn stalks, etc., may also be turned under in soils to increase their organic matter content. In general it may be said that all means which may be employed to increase the organic matter content of soils will have an important influence in preventing erosion. Growing of crops. — The growing of crops, such as alfalfa, that remain on the land continuously for a period of two or more years is often advisable on steep hillsides. Alsike clover, sweet clover, timothy and red top are also (|uite neces- sary for use in such locations. The root system of such crops as these holds the soil together and the washing action of rainfall is reduced to a nuirked extent. Contour discing. — Discing around a hill instead of up and down the slope or at an angle to it is fre(iuently very effective in preventing erosion. This prac- tice is "called "contour discing" and it has proven quite satisfactory in many cases in Iowa. Contour discing is practiced to advantage on stalk ground in the spring, preparatory to seeding small grain, and also on fall plowed land that is tobe planted to corn. It is advisable in contour discing to do the turning row along the fence, up the slope, first as the horses and disc when turning will pack and cover the center mark of the disc, thus leaving no de{)rehsion to foim a water channel. Deep plowing. — Deep plowing increases the absorptive power of the soil and hence decreases erosion. It is especially advantageous if it is done in the fall as the soil is then put in condition to al)sorb and hold the largest possible amount cf the late fall and early spring rains. It is not advisable, however, to change from shallow plowing to deep plowing at a single operation as too much subsoil may be mixed with the surface soil and the productive power of the soil there- fore reduced. A gradual deepening of the surface soil by increasing the depth of plowing will be of value both in increasing the feeding zone of plant roots: tind in making the soil more absorptive and therefore less subject to erosion. INDIVIDUAL SOIL TYPES IN POTTAWATTAMIE COUNTY* LOESS SOILS There are two soil areas in Pottawattamie county which are classed as loess soils, the Marshall silt loam and the Knox silt loam. These two types cover over 72 per cent of the area of the county and constitute, therefore, the most important soils MARSHALL SILT LOAM (9) This soil type covers 68 per cent of the area of Pottawattamie county. In depth, the surface soil ranges from 10 to 24 inches, while the subsoil extends to a depth of 10 to 20 feet in the more shallow deposits, and from 20 to 80 feet in the more fully developed deposits. When wet the surface soil is a solid black; near the line between the ^oil and subsoil the color becomes lighter and * Tlie (lescri])tions of individual soil types ^iven in the Bureau of Soils report on Pottawat- tamie county, Iowa, have been rather closely followed in this section of the report. POTTAWATTAMIE COUNTY SOILS 35 sometimes a mottling of yellow, gray or drab is found. When timbered the soil is lighter in color than where it is in prairie. Only in a few cases, at the base of high hills, is there any occurrence of gravel or sandy material. Lime concretions are found in the subsoil. These vary in size from one-half inch to six inches in diam«4er and in some localities occur in considerable numbers. In other cases, as has been noted, they are absent and the soil type is acid. The topography of this soil is nearly level to undulating, rolling, or hilly. It occupies an elevation thruout the county ranging from 1,000 to 1,200 feet above sea level. The natural drainage is very thoro. The streams have often cut deep channels and some bad cases of erosion are found on these hill slopes. General farm crops such as corn, oats, and wheat produce satisfactory yields on this soil and they are the principal crops grown. The average yields of these crops are greater on this type than for the county as a whole, indicating quite distinctly their adaptation to this soil. Alfalfa is particularly well suited to this soil and it is being grown on rapidly increasing areas. Other legumes, such as red clover and sweet clover, also do well. The production of grapes and apples is unusually good on this type and the number of vineyards and orchards is becoming greater as the value of these crops is recognized. Veg- etables, such as tomatoes, potatoes, beans, cabbage, eggplant, beets, turnips, and parsnips, grow well on this soil but they are not cultivated to any consid- erable extent for marketing. The chief need of this soil type, as has been pointed out in the previous pages, is for organic matter. The greenhouse and field experiments have shown irn- usually large effects from the application of farm manure. This material ap- parently supplies the conditions which are necessary in this soil for the best growth of crops. Lime is sometimes necessary, as in many instances the orig- inal content has been completely lost by leaching, and tests should always be carefully made for acidity. Conrmercial fertilizers seem to be unnecessary at the present time. Phosphorus, however, is low in the soil and applications show slight increases. This leads to the conclusion that this element will be necessary in the more or less distant futirre. Oi-ganic matter, however, either as farm manure or as green manures, seems to be the best material to be applied to the soil at the present time and the results secured with the irse of these substances show thenr to be of economic value. KNOX SILT LOAM (11) This soil covers -4.7 per cent of the area of the county. The surface soil ex- tends to a depth of 15 to 20 inches where it grades into a light-brown to buff- colored silt loam. There is no sharp line of separation between the surface soil and subsoil, the yellowish-browu soil gradually merging into the yellow subsoil. In some places the surface soil is somewhat darker than the true soil type and resembles more nearly the ^Marshall silt loam. The texture of the soil is practically a silt loam to a depth of 10 to oO feet, only a small quantity of clayey or sandy material being encountered within the 3-foot soil section. Sand and stones are normally absent. In local areas, how- ever, where there has been some wash from other soils there is occasionally a little sand. 36 SOIL SURVEY OF IOWA This soil type occurs in a narrow strip bordering the lowlands of the Missouri river and is characterized by steep bluffs and a generally rough topography. The bluffs rise 100 to 150 feet above the lowlands. The drainage is normally good ; in places where there are steep, unprotected slopes, it is excessive. ]\Iany gulches or drainage ways occur in the bluff section, and the slopes leading to stream channels are frequently so steep as to prohibit cultivation. This soil is especially adapted for the production of grapes and many large vineyards are found on it. The steep slopes on which it occurs can be utilized very satisfactorily for vineyards when other crops do not do well. Practically all the grape gromng in the county occurred on this soil a few years ago, but now the Marshall silt loam is also being used for this crop. With the better methods of soil treatment, pruning, etc., which are being followed, grapes are becoming a more and more valuable crop. On the more level slopes, the ordi- nary farm crops and many vegetables do well on this soil. Orcharding is also profitable and the growing of apples and other fruits is increasing. This soil is especially deficient in organic matter, and it therefore is in need of farm yard manure and green manure crops. It is not generally acid and is not in striking need of phosphorus, but the latter element will soon be neces- sary. The chief needs of this type to make it more productive are the use of methods to prevent erosion which is so often extensive and the abundant appli- cation of farmyard manure or the turning under of green manure crops. TERRACE SOILS There are three terrace soils in Pottawattamie county included in the Han- cock series and the Osgood series. These three types are all of minor import- ance in the county, covering only 3.3 per cent of the total area. HANCOCK SILT LOAM (23) This terrace soil is a second bottom soil bordering the overflowed bottoms of some of the main drainage ways of the county, especially the East and West Nishnabotna rivers and the creeks. The surface soil extends to a depth of 12 to 15 inches, grading into a lighter subsoil from Chocolate brown to mottled yel- lowish-brown and gray, and ranging in texture from a silt loam to a silty clay loam. In some places layers of very fine sandy material are found. Evidence is frequently found of the alluvial nature of this soil, but it also receives the wash from the surrounding soil and is somewhat variable in composition. This type is almost level, sloping gently toward the streams in some cases. In general it is very well drained, but the water may stand in level areas and in depressions after heavy rains and in such cases artificial drainage is re- quired. Com is grown the most extensively of any crop on this soil and its value is the greatest. Wheat is also grown to a considerable extent and produces satis- factory yields. Other crops such as alfalfa, clover, timothy and rape, and truck crops such as cabbage, tomatoes, squash, beans, potatoes, etc., do well but they are not grown in any large quantities. This soil is not so low in organic matter as the loess soils, but it will respond to applications of farmyard manure, and these should therefore be made. Drain- POTTAWATTAMIE COUNTY SOILS 37 lir" i "y' m^' y » yy > i ^ >!;i ^^^-j** •H -+H — S'^o CC d !D =! O -ti -r*^ 3 O o =^ — 1 a; o o Ss.-S^ :^-E S o c >, « ci 03 <« r- « r- 38 SOIL SURVEY OF IOWA Il>; >rf. aj _C _2 •;- -I-' *j i- .- ^; ^ O - ^ . ■- _ X' _ OC « O) pi o -^' S "x .^ . ^ X a6o«-^g o§ ^f r-a -^^ -i® .• t- O HH [B !« .-I -I- -1- "' Oi POTTAWATTAMIK COUNTY SOILS 39 age of some areas is necessary' and the use of phosphorus may be required in the near future. Lime is not necessary at the present time. HANCOCK SILTY CLAY^ (24) This soil is a minor type in Pottawnttainie county. The surface soil is only 4 to 6 inches in depth, and the subsoil extends to 12 to 15 inches, giving way below to a gray and brown mottled or drab heavy plastic clay which ex- tends to three feet or more. The topography of this soil is level, a gentle slope toward the river being noticeable, llnderdrainage is generally well established, but in some ca>-es the water stands in depressions and makes the soil slippery and muddy. Corn, alfalfa and truck crops, such as beets, tomatoes, cabbage, potatoes and beans give good yields on this soil, corn and alfalfa being especially valuable. The needs of this soil, apart from diaina^e which is the first essential, include the use of organic matter and phosi)liorus altho neither of these materials is so necessary as on the loess soils or the other terrace types. OSGOOD VERY FINE SAND (25) This type is mapped only in four very small areas near the Missouri river, west and south of Council Bluffs. The surface soil extends to 12 to 15 inclies and grades into the lighter subsoil of the same texture throughout the 3-foot section. It is almost level in topography and possesses a very loose structure, hence the drainage is excessive. Crops are apt to suffer for moisture on this soil dur- ing dry seasons. It is very low in organic matter and hence its chief need is for farm yard manure or green manure crops. These materials would not only provide better mechanical soil conditions, preventing the rapid drying out, but they would supply plant food and enable proper decomposition processes to occur. These materials together with phosphorus fertilizers which will undoubtedly be nec- essary in the near future will make this soil type more productive. It is an extreme type and of small occurrence, but it is worth special effort to make it fertile. When well fertilized, early truck crops, melons and cantaloupes can profitably be grown on this soil. General farm crops such as corn nuiy also be grown satisfactorily. SWAMP AND BOTTOMLAND SOILS Five tj^pes of soil are included in the group of swamp and bottomland soils. The total area covered by them is 24 per cent of the area of the county, and in- cludes the Wabash and Sarpy soils. WABASH SILT LOAM (26) This soil type covers over 13 per cent of the area of Pottawattamie county and it is largely developed thruout the county along the overflowed bottoms of Walnut and Pigeon creeks. The surface soil of this type, which grades from a dark-brown to almost black mellow silt loam, ranges from 8 to 15 inches in depth and in places ex- 40 SOIL SURVEY OF IOWA tends as deep as 25 inches. The subsoil is lighter in color, varying from a light- brown to mottled yellow and gray heavy silt loam. Pockets of sand occur in places. The topography of this type is almost level. It occupies the first bottoms and is therefore subject to overflow at least in part. The type as a whole suf- fers considerably from erosion, especially those portions adjoining the streams. Frequently rather considerable areas are removed from one place to another. Straightening the channels of the streams is the best way to protect the land. The portions of the soil near the uplands adjoining the terrace soils are fairly well drained, while the lower flat areas are of course poorly drained. The deepening of the streams by dredging will lower the water level and make these flat areas more productive and the crop less liable to be flooded out. Corn is the most important crop grown on this soil. Oats and other farm crops which can be planted and harvested the same season also do well. Winter wheat or long season crops are liable to injury from drowming out, or from the heaving of the land under the action of the winter freezes. Much of the type is seeded to grass and makes an excellent pasture. Alfalfa can be grown provided the stream channels are straightened and the water level lowered to at lea^ 5 feet below the surface. The low lying parts of this soil are allowed to grow up to native grasses and serve as pasture land. The Wabash silt loam is fairly well supplied with plant food, but like the other soils in the county it is rather low in organic matter and phosphorus and these are the constituents which are necessary to make it fertile. That is, after the soils have been protected from flooding, the next requisite is the use of farm manure or green manures, preferably the former, to start the proper decomposi- tion processes and supply the best physical conditions. Phosphorus will be necessary in the near future for the phosphorus content is so low that crops will soon be in need of that element. Lime is not necessary in general at the present time, but it probably will be required in a short time on this soil when under intensive cultivation. With these treatments, crop production should be very satisfactory and the permanent fertility of the soil should be maintained. WABASH SILT LOAM (COLLUVIAL PHASE) (26a) (This type is indicated on the map by number 26, but is shown in a darker color than the typical Wabash silt loam.) This soil type occurs thruout the county in a narrow strip of alluvial and colluvial material along the minor streams and drainage ways. This material also occurs on the outer edge of the lowlands along nearly all the larger streams, but the areas are in many cases too narrow to be shown on the map. The color of the soil is practically the same as that of the true Wabash silt loam and it is somewhat similar in other characteristics. In many places it is flooded at periods of heavy rainfall, but as it occurs on steep slopes the surplus water runs off quite rapidly and in general it may be said that it is not in need of drainage. In this respect, therefore, it differs from the Wabash silt loam. Practically all the crops grown in the county seem to do well on this phase. Com is the most important crop, both in acreage and production. Wheat, oats, rye, barley, alfalfa, timothy, clover and small truck crops are also grown ex- POTTAWATTAMIE COUNTY SOILS 41 tensively. Oats and spring wheat do not usually do as Avell as on the upland soils but the yields of some of the other crops mentioned are frequently quite as satisfactory as on the better types of soil. Much of the phase which lies above overflow is seeded to alfalfa, red clover and rape, all of which do well. The low-lying portions are often allowed to grow up to native grasses and used for pasture. The varying conditions under which this type occurs with respect to overflow, drainage, and general location, make it exceedingly variable in value and the land sells for $75 to $150 per acre. In chemical composition, the soil is practically the same as the main type and hence its needs are very similar. It is quite low in organic matter and phosphorus and it should receive applications of farm manure and green manures in order to bviild it up in humus, and in the near future phosphorus fertilizers must be used. With these treatments and the application of lime, if found necessary in special cases, this soil can be made very productive and kept so, provided of course it is protected from flooding. WABASH SILTY CLAY (27) This soil covers about 8 per cent of the area of the county. It is also locally kno\ATi as "gumbo." It occupies level or depressed areas within the broader bottomlands, and is typically developed along the first bottoms of the East and West Nishnabotna rivers and along the Missouri river, lying somewhat back from the main stream channel. The surface soil extends to a depth of 4 to 6 inches and rests on a heavy, stiff, sticky, plastic clay, bluish gray or drab to gray and brown mottled in color. The surface soil when wet becomes slippery and on drying cracks and separates into irregular cakes or blocks. In places fine sand is mixed with the clay, lying between two layers of heavy clay. It is subject to overflow, but the larger portion of the type is quite suitable for agricultural purposes when well drained. The lower depressions and old lake beds retain excessive amounts of moisture and cannot be cultivated. Even protected areas are apt to be covered during freshets, the water covering the soil until after planting time. Very little tile drainage has been done and the cost is great. The proper drainage of the soil is, however, the prime essential for the preparation of the soil for crop gro\\i:h and the cost involved is more than offset by the returns secured. Wlien this is accomplished, proper cultiva- tion and treatment will make the soil very productive, provided of course, that the rainfall is not so heavy that the soil is flooded. The time of plowing is very important. The soil should neither be too wet nor too dry when plowed or it will be lumpy and difficult to cultivate. The addition of farm manure and green manures would prove of value on this soil. Phosphorus will be required and may be necessary now, and lime while not needed at the present time, must be used sooner or later. Proper drainage and fall plowing have been found to be very effective in making this "gumbo" soil productive. Under such treatment land of little value may be made equal in value to the best land in the state. Com is the principal crop gro\^^l on this soil, and gives satisfactory yields. Oats, spring wheat and al- 42 SOIL SURVEY OF IOWA falfa also do well altho the small grains often grow so rank that tliey lodge. Bluegrass is growTi on the lower more poorly drained areas and the pastures are used for fattening beef cattle. SABPY VERY FINE SANDY LOAM (28) This soil type is of minor impoi'tance in Pottawattamie eonnty, covering only 1.8% of its area. It is usually associated with the Wabash silty clay just de- scribed, but it occupies a somewhat higher elevation above the main channel of the river. The surface soil is 10 to 15 inches deep and varies from a light-brownis«h gray to grayish-brown veiy fine sandy loam and the subsoil is very similar in color, but is generally more open in structure and coarser in texture. The percentage of sand increases with the depth, the soil often grading into a fine sand at a depth of thirt.y-six inches or more. The topography is level to slightly undulating, with occasional sandy ridges. The drainage is good. Like the other bottomland soils, this type is subject to overflow and there is danger of floods during the growing sea.son, causing loss of crops. Com is the main crop grown on this soil and the yields are quite satisfactory. Wheat, oats, timothy, clover and alfalfa are grown to a small extent. Alfalfa gives good yields but is apt to be drowned out by flood waters. Truck crops such as sweet potatoes, Irish potatoes, cabbage, melons and cantaloupes are being grown in increasing quantities and are proving quite profitable. The use of the soil for pasture crops is also profitable. The main need of this soil type is for organic matter. It is particularly de- ficient in this material and should receive heavy applications of farmyard manure. Green manure crops should also be used in addition to the farm manure to supply the necessary organic matter. Phosphorus is also necessary or will soon be required, and lime must un- doubtedly be used in the near future. With the proper supply of organic mat- ter and phosphorus and lime the soil can be made very fertile and kept so. SARPY VERY FINE SAND (29) This soil type is of extremely minor importance, covering only 0.4% of the total area of the county. There are a few small areas along the old channels of the ]\rissouri river, occurring as long, narrow ridges, and also in the flood plains adjoining the river. These fine sands are easily moved by the wind and are constantly shifting. The surface soil occurs to a depth of 10 to 15 inches and grades into a darker colored sand, the texture remaining the same, through the three-foot section. The topography of these sand areas is level to gently undulating, altho in a few places small sand dunes have been found. Corn, watermelons and canta- loupes are the principal crops grown on this soil. Corn does only fairly well, but melons prove quite profitable. The chief use of this soil is for pasture. The soil is so loose and open in texture that the drainage is excessive. The chief need of this soil type therefore is the use of humus-forming materials to improve the physical, chemical and bacteriological conditions in the soil. Farm- POTTAWATTAMIE COUNTY SOILS 43 3t 31 B v^^ivi^llW i.^x i.^- 4 1^ \ 1 , 29 B »^^ •":* :'-.. nil 3° B i_- F\iy. 9. SuitMco, siihsuii'ace and subsoils of tliree of the individual soil types of I'ottawatta- niie county 31. Sarpy very line sandy loam 29. Knox silt loam :w. Marshall silt loam yard manure will sen-o this purpose, but leguminous green manures have lieen found on similar soils to be particularly efficient in building them up and mak- ing them productive. Such green manures not only «upply organic nuitter, but also nitrogen and are, therefore, doul)ly efficient. Phosphorus is also lacking in this soil and should be applied if satisfactory yields are to be secured. Lime is not necessary at the present time, but undoubtedly will be in the near future. When proper 'methods of ti'eatment are followed and satisfactory crop yields are secured, this material will soon bccouit deficiuit and will need to be sup- plied. Such light soils can be built up into a satisfactory state of fertility and maintained so if the above methods of treatment are carefullv cari'ied out. I APPENDIX THE SOIL SURVEY OF IOWA What soils need to make them highly productive and to keep them so, and how their needs may be supplied are problems which are met constantly on the farm today. To enable every Iowa farmer to solve these problems for his local conditions, a complete survey and study of the soils of the state has been undertaken, the results of which will be published in a series of county reports. This work includes a detailed survey of the soils of each county, following which all the soil types, streams, roads, railroads, etc., are accurately located on a soil map. This portion of the work is being carried ou in cooperation with the Bureau of Soils of the United States Department of Agriculture. Samples of soils are taken and examined mechanically and chemically to determine their character and composition and to learn their needs. Pot experiments with these samples are conducted in the greenhouse to ascertain the value of the use of manure, fertilizers, lime and other materials on the various soils. These pot tests are followed in many cases by field experiments to check the results secured in the greenhouse. The meagerness of the funds available for such work has limited the extent of these field studies and tests have not been possible in each county surveyed. Fairly complete results have been secured, however, on the main soil types in the large soil areas. Following the survej^, systems of soil management which should be adopted in the various counties and on the different soils are worked out, old methods of treatment are emphasized as necessary or their discontinuance advised, and new methods of proven value are suggested. The published reports as a whole will outline the methods which the farmers of the state must employ if they wish to maintain the fertility of their soils and insure the best crop produc- tion. The various counties of the state will be surveyed as rapidly as funds will permit, the number included each year being determined entirely by the size of the appropriation avail- able for the work. The order in which individual counties will be chosen depends very largely upon the interest and demand in the county for the work. Petitions signed by the residents, and especially by the farmers or farmers' organizations of the county, should be submitted to indicate the sentiment favorable to the undertaking. Such petitions are filed in the order of their receipt and aid materially in the annual selection of counties. The reports giving complete results of the surveys and soil studies in the various counties will be published in a special series of bulletins, as rapidly as the work is completed. Some general information regarding the principles of permanent soil fertility and the character, needs and treatment of Iowa soils, gathered from various published and unpublished data accumulated in less specific experimental work will be included in or appended to all the reports. PLANT FOOD IN SOILS Fifteen different chemical elements are essential for plant food, but many of these occur so extensively in soils and are used in such small quantities that there is practically no danger of their ever running out. Such, for example, is the case with iron and aluminum, past experience showing that the amount of these elements in the soil remains practfically constant. Furthermore, there can never be a shortage in the elements which come primarily from the air, such as carbon and oxygen, for the supply of these in the atmosphere is practically in- exhaustible. The same is true of nitrogen, wliich is now known to be taken directly from the atmosphere by well-inoculated legumes and by certain microscopic organisms. Hence, altho many crops are unable to secure nitrogen from the air and are forced to draw on the soil supply, it is possible by the proper and frequent growing of well-inoculated legumes and their use as green manures, to store up sufficient of this element to supply all the needs of succeeding non-legumes. Knowledge of the nitrogen content of soils is important in showing whether sufficient green 46 SOIL SURVEY OF IOWA Fig. 10. Map of Iowa showing the counties surveyed manure or barnyard manure has been applied to the soil. Commercial nitrogenous fertilizers are now known to be unnecessary where the soil is not abnormal, and green manures may be used in practically all cases. Where a crop must be "forced," as in market gardening, some nitrogenous fertilizer may be of value. THE "SOIL DERIVED" ELEMENTS Phosphorus, potassium, calcium and sulfur, known as "soil-derived" elements, may fre- quently be lacking in soils, and then a fertilizing material carrying the necessary element must be used. Phosphorus is the element most likely to be deficient in all soils. This is especially true in Iowa soils. Potassium frequently is lacking in peats and swampy soils, but normal soils in Iowa and elsewhere are usually well supplied with this element. Calcium may be low in soils which have borne a heavy growth of a legume, especially alfalfa; but a shortage in this element is very unlikely. It seems possible from recent tests that sulfur may be lacking in many soils, for applications of sulfur fertilizers have proven of value in some cases. How- ever, little is known as yet regarding the relation of this element to soil fertility. If later studies show its importance for plant growth and its deficiency in soils, sulfur fertilizers may come to be considered of much value. If the amounts of any of these soil-derived elements in soils are very low, they need to be supplied thru fertilizers. If considerable amounts are present, fertilizers containing them are unnecessary. In such cases if the mechanical and humus conditions in the soil are at the best, crops will be able to secure sufficient food from the store in the soU. For example, if potas- sium is abundant, there is no need of applying a potassium fertilizer ; if phosphorus is deficient, a phosphate should be applied. If calcium is low in the soil, it is evident that the soil is acid and lime should be applied, not ony to remedy the scarcity of calcium, but also to remedy the injurious acid conditions. AVAILABLE AND UNAVAILABLE PLANT FOOD Frequently a soil analysis shows the presence of such an abundance of the essential plant foods that the conclusion might be drawn that crops should be properly supplied for an in- definite period. However, application of a fertilizer containing one of the elements present in such large quantities in the soil may bring about an appreciable and even profitable increase in crops. The explanation of this peculiar state of affairs lies in the fact that all the plant food POTTAWATTAMIE COUNTY SOILS 47 shown by analysis to be present in soils is not in a usable form; it is said to be unavailable. Plants cannot take up food unless it is in solution; hence available plant food is that which is in solution. Analyses show not only this soluble or available portion but also the very much larger insoluble or unavailable part. The total amount of plant food in the soil may, tiiere- fore, be abundant for numerous crops, but if it is riot made available rapidly enough, plants will suffer for proper food. Bacteria and molds are the agents which bring about the change of insoluble, unavailable material into an available form. If conditions in the soil are satisfactory for their vigorous growth and sufficient total plant food is present, these organisms will bring about the produc- tion of enough soluble material to support good crop growth. The soil conditions necessary for the best growth and action of bacteria and molds are the same as those which are required by plants. The methods necessary to maintain permanent soil fertility will, therefore, insure satisfactory action of these organisms and the sufficient production of available plant food. The nitrogen left in the soil in plant and animal remains is entirely useless to plants and must be changed to be available. Bacteria bring about this change and they are all active in nor- mal soils which are being properly handled. Phosphorus is found in soil mainly in the mineral known as apatite and in other insoluble substances. Potassium occurs chiefly in the insoluble feldspars. Therefore, both of these ele- ments, as they normally occur in soils, are unavailable. However, the grovrth of bacteria and molds in the soil brings about a production of carbon dioxide and organic acids which act on the insoluble phosphates and potassium compounds and make them available for plant food. Calcium occurs in the soil mainly in an unavailable form, but the compounds containing it are attacked by the soil water carrying the carbon dioxide produced by bacteria and molds and as a result a soluble compound is formed. The losses of lime from soils are largely the result of the leaching of this soluble compound. Sulfur, like nitrogen, is present in soils chiefly in plant and animal remains in which form it is useless to plants. As these materials decompose, however, so-called sulfur bacteria ap- pear and bring about the formation of soluble and available sulfates. The importance of bacterial action in making the store of plant food in the soil available is apparent. With proper physical and chemical soil conditions, all the necessary groups of bac- teria mentioned become active and a vigorous production of soluble nitrogen, phosphorus, potassium, calcium and sulfur results. If crops are to be properly nourished care should al- ways be taken that the soil be in the best condition for the growth of bacteria. EEMOVAL OF PLANT FOOD BY CROPS The decrease of plant food in the soil is the direct result of removal by crops, although there is often some loss by leaching also. A study of the amounts of nitrogen, phosphorus, and potassium removed by some of the common farm crops will show how rapidly these ele- ments are used up under average farming conditions. The amounts of these elements in various farm crops are given in table I. The amount of calcium and sulfur in the crops is not included as it is only recently that the removal of these elements has been considered important enough to warrant analyses. The figures in the table show also the value of the three elements contained in the different crops, calculated from the market value of fertilizers containing them. Thus the value of nitrogen is figured at 16 cents per pound, the cost of the element in nitrate of soda; phos- phorus at 12 cents, the cost in acid phosphate, and potassium at 6 cents, the cost in muriate of potash. It is evident from the table that the continuous growing of any common farm crop without returning these three important elements will lead finally to a shortage of plant food in the soil. The nitrogen supply is drawn on the most heavily by all the crops, but in the case of alfalfa and clover only a small part should be taken from the soil. If these legumes are in- oculated as they should be, they will take most of their nitrogen from the atmosphere. The figures are therefore entirely too high for the nitrogen taken from the soil by these two crops, but the loss of nitrogen from the soil by removal in non-leguminous crops is considerable. The phosphorus and potassium in the soil are also rapidly reduced by the growth of ordinary crops. While the nitrogen supply may be kept up by the use of leguminous green manure crops, phosphorus and potassium must be supplied by the use of expensive commercial fer- tilizers. The cash value of the plant food removed from soils by the growth and sale of various crops is considerable. Even where the grain alone is sold and the crop residues are returned to the soil there is a large loss of fertility, and if the entire crop is removed and no return made, the 48 SOIL SURVEY OF IOWA TABLE I. PLANT FOOD IN CROPS AND VALUE Calculating Nitrogen (N) at 16c (Sodium Nitrate (NaNOs)), Phosphorus (P) at 12c (Acid Phosphate), and Potassium (K) at 6c (Potassium Chloride (KCl)) Yield Plant Food, Lbs. Value of Plant Food Total Value Crop Nitrogen Phos- phorus Potassium Nitrogen Phos- phorus Potassium of Food Plant Corn, grain Corn, stover Corn crop Wheat, grain Wheat, straw Wheat, crop Oats, grain Oats, straw Oats crop Barley grain Barley straw Barley crop Rye grain Rye straw Rye crop Potatoes Alfalfa hay Timothy hay Clover hay 75 bu. 2.25 T. 30 bu. 1.5T. 50 bu . 1.25 T. 30 bu. 0.75 T. 30' bu." 1.5T. 300 bu. 6T. 3T. 3T. 75 36 111 42.6 15 57.6 33 15.5 48.5 23 9.5 32.5 29.4 12 41.4 63 300 72 120 12.75 4.5 17.25 7.2 2.4 9.6 5.5 2.5 8 5 1 6 6 3 9 12.7 27 9 15 14 39 53 7.8 27 34.8 8 26 34 5.5 13 18.5 7.8 21 28.8 90 144 67.5 90 $12.00 5.76 17.76 6.81 2.40 9.21 5.28 2.48 7.76 3.68 1.52 5.20 4.70 1.92 6.62 10.08 48.00 11.52 19.20 $1.53 0.54 2.07 0.86 0.28 1.14 0.66 0.30 0.96 0.60 0.12 0.72 0.72 0.36 1.08 1.52 3.24 1.08 1.80 $0.84 2.34 3.18 0.46 1.62 2.08 0.48 1.56 2.04 0.33 0.78 1.11 0.46 1.26 1.72 5.40 8.64 3.95 5.40 $14.37 8.64 23.01 8.13 4.30 12.43 6.42 8.28 14.70 4.61 2.42 7.03 5.88 3.54 9.42 17.00 59.88 16.55 16.40 loss is almost doubled. It is evident, therefore, that in calculating the actual income from the sale of farm crops, the value of the plant food removed from the soil should be subtracted from the proceeds, at least in the case of constituents which must be replaced at the present time. Of course, if the crops produced are fed on the farm and the manure is carefully preserved and used, a large part of the valuable matter in the crops will be returned to the soil. This is the case in livestock and dairy farming where the products sold contain only a portion of the valuable elements of plant food removed from the soil. In grain farming, however, green manure crops and commercial fertilizers must be depended upon to supply plant food de- fiencies in the soil. It should be mentioned that the proper use of crop residues in this latter system of farming reduces considerably the loss of plant food. REMOVAL PROM IOWA SOILS It has been conservatively estimated that the plant food taken from Iowa soils and shipped out of the state in grain amounts to about $30,000,000 annually. This calculaion is based on the estimate of the secretary of the Western Grain Dealers' Association that 20 per cent of the corn and 35 to 40 per cent of the oats produced in the state is shipped off the farms. This loss of fertility is unevenly distributed over the state, varying as farmers do more or less livestock and dairy farming or grain farming. In grain farming, where no manure is produced and the entire grain crop is sold, the soil may very quickly become deficient in cer- tain necessary plant fo4pcls. Eventually, however, all soils are depleted in essential food mate- rials, whatever system of farming is followed. This loss of fertility is great enough to demand serious attention. Careful consideration should certainly be given to all means of maintaining the soils of the state in a permanently fertile condition. PERMANENT FERTILITY IN IOWA SOILS The preliminary study of Iowa soils, already reported,* revealed the fact that there is not an inexhaustible supply of nitrogen, phosphorus and potassium in the soils of the state. Po- tassium was found in much larger amounts than the other two elements, and it was concluded, therefore, that attention should be centered at the present time on nitrogen and phosphorus. In spite of the fact that Iowa soils are still comparatively fertile and crops are still large, * Bulletin 150 Iowa Agricultural Experiment Station. POTTAWATTAMIE CXDUNTY SOILS 49 there is abundant evidence at hand to prove that the best possible yields of certain crops are not being obtained in many cases because of the lack of necessary plant foods or because of the lack of proper conditions in the soil for the growth of plants and the production, by bac- teria, of available plant food. Proper systems of farming will insure the production of satisfactory crops and the mainten- nance of permanent fertility and the adoption of such systems should not be delayed until crop yields are much lower, for then it will involve a long, tedious and very expensive fight to bring the soil back to a fertile condition. If proper methods are put into operation while comparatively large amounts of certain plant foods are still present in the soil, it is relatively easy to keep them abundant and attention may be centered on those other elements which are likely to be limiting factors in crop production. Soils may be kept permanently fertile by adopting certain practices which will be sum- marized here. CULTIVATION AND DEAINAGE Cultivation and drainage are two of the most important farm operations in keeping the soil in a favorable condition for crop production, largely because they help to control the moisture in the soil. The moisture in soils is one of the most important factors governing crop production. If the soil is too dry, plants suffer for a lack of the water necessary to bring them their food and also for a lack of available plant food. Bacterial activities are so restricted in dry soils that the production of available plant food practically ceases. If too much moisture is present, plants likewise refuse to grow properly because of the exclusion of air from the soil and the absence of available food. Decay is checked in the absence of air, all beneficial bac- terial action is limit-ed and humus, or organic matter, containing plant food constituents in an unavailable form, accumulates. The infertility of low-lying, swampy soils is a good illus- tration of the action of excessive moisture in restricting plant growth by stopping aeration and limiting beneficial decay processes. While the amount of moisture in the soil depends very largely on the rainfall, any excess of water may be removed from the soil by drainage and the amount of water present in the soil may be conserved during periods of drought by thoro cultivation or the maintaining of a good mulch. The need for drainage is determined partly by tlie nature of the soil, but more particularly by the subsoil. If the subsoil is a heavy, tight clay, a surface clay loam will be rather readily affected by excessive rainfall. On the other hand, if the surface soil is sandy, a heavy subsoil will be of advantage in preventing the rapid drying out of the soil and also in checking losses of valuable matter by leaching. Many acres of land in the Wisconsin drift area in Iowa have been reclaimed and made fertile thru proper drainage, and one of the most important farming operations is the laying of drains to insure the removal of excessive moisture in heavy soils. The loss of moisture by evaporation from soils during periods of drought may be checked to a considerable extent if the soil is cultivated and a good mulch is maintained. Many pounds of valuable water are thus held in the soil and a satisfactory crop growth secured when otherwise a failure would occur. Other methods of soil treatment, such as liming, green manuring and the application of farm manures, are also important in increasing the water- holding power of light soils. THE ROTATION OF OEOPS Experience has shown many times that the continuous growth of one crop takes the fer- tility out of a soil much more rapidly than a rotation of crops. One of the most important farm practices, therefore, from the standpoint of soil fertility, is the rotation of crops on a basis suited to the soil, climatic, farm and market conditions. The choice of crops is so large that no diflieulty should be experienced in selecting those suitable for all conditions. Probably the chief reason wliy the rotation of crops is beneficial may be found in the fact that different crops require different amount of the various plant foods in the soil. One par- ticular crop will remove a large amount of one element and the next crop, if it be the same kind, will suffer for a lack of tliat element. If some other crop, which does not draw as heav- ily on that particular plant food, is rotated with the former crop, a balance in available plant food is reached. Where a cultivated crop is grown continuously, there is a much greater loss of organic matter or humus in the soil than under a rotation. This fact suggests a second explanation for the beneficial effects of crop rotations. With cultivation, bacterial action is much increased and the humus in the soil may be decomposed too rapidly and the soil injured by the removal of the valuable material. Then the production of available plant food in the soil will bo 50 SOIL SUEVEY OF IOWA hindered or stopped and crops may suffer. The use of legumes in rotations is of particular value since when they are well inoculated and turned under they not only supply organic mat- ter to the soil, but they also increase the nitrogen content. There is a third explanation of the value of rotations. It is claimed that crops in their growth produce certain substances called "toxic" which are injurious to the same crop, but have no effect on certain otlier crops. In a proper rotation the time between two different crops of the same plant is long enough to allow the "toxic" substance to be disposed of in the soil or made harmless. This theory has not been commonly accepted, chiefly because of the lack of confirmatory evidence. It seems extremely doubtful if the amounts of these "toxic" substances could be large enough to bring about the effects evidenced in continuous cropping. But, whatever the reason for the bad effects of continuous cropping, it is evident that for all good systems of farming some definite rotation should be adopted, and that rotation should contain a legume, because of the value of such crops to the soil. In no other way can the humus and nitrogen content of soils be kept up so cheaply and satisfactorily as by the use of legumes, either as regular or "catch" crops in the rotation. MANUEING There must always be enough humus, or organic matter, and nitrogen in the soil if satis- factory crops are to be secured. Humus not only keeps the soil in the best physical condition for crop growth, but it supplies a considerable portion of nitrogen. An abundance of humus may always be considered a reliable indication of the presence of much nitrogen. This nitro- gen does not occur in a form available for plants, but with proper physical conditions in the soil, the nonusable nitrogen in the animal and vegetable matter which makes up the humus, is made usable by numerous bacteria and changed into soluble and available nitrates. The humus, or organic matter, also encourages the activities of many other bacteria which produce carbon dioxide and various acids which dissolve and make available the insoluble phos- phorus and potassium in the soil. Three materials may be used to supply the organic matter and nitrogen of soils. These are farm manure, crop residues and green manure, the first two being much more common. Farm manure is composed of the solid and liquid excreta of animals, litter, unconsumed food and other waste materials, and supplies an abundance of organic matter, much nitrogen and millions of valuable bacteria. It contains, in short, a portion of the plant food present in the crops originally removed from the soil and in addition the bacteria necessary to prepare this food for plant use. If it were possible to apply large enough amounts of farm manure, no other material would be necessary to keep the soil in the best physical condition, insure efiicient bacterial action and keep up the plant food supply. But manure cannot serve the soil thus efficiently, for even under the very best methods of treatment and storage, 15 per cent of its valuable constituents, mainly nitrogen, are lost. Furthermore, only in a very few instances is enough produced on a farm to supply its needs. On practically all soils, there- fore, some other material must be applied with the manure to maintain fertility. Crop residues, consisting of straw, stover, roots and stubble, are important in keeping up the humus, or organic matter content of soils. Table I shows that a considerable portion of the plant food removed by crops is contained in the straw and stover. On all farms, therefore, and especially on grain farms, the crop residues should be returned to the soil to reduce the losses of plant food and also to aid in maintaining the humus content. These materials alone are, of course, insufficient and farm manure must be used when possible, and green manures also. Green manuring should be followed to supplement the use of farm manures and crop resi- dues. In grain farming, where little or no manure is produced, the turning under of legumin- ous crops for green manures must be relied upon as the best means of adding humus and nitrogen to the soil, but in all other systems of farming also it has an important place. A large number of legumes will serve as green manure crops and it is possible to introduce some such crop into almost any rotation without interfering with the regular crop. It is this pecu- liarity of legumes, together with their ability to use the nitrogen of the atmosphere when well inoculated, and thus increase the nitrogen content of the soil, which gives tliom their great value as green manure crops. It is essential that the legumes used be well inoculated. Their ability to use the atmos- pheric nitrogen depends on that. Inoculation may be accomplished by the use of soil from a field where the legume has previously been successfully grown and well inoculated, or by the use of inoculating material that may be purchased. If the legume has never been grown on the soil before, or has been grown without inoculation, then inoculation should be practiced by one of these methods. POTTAWATTAMIE COUNTY SOILS 51 By using aU the crop residues, all the manure produced on the farm, and giving well in- oculated legumes a place in the rotation for green manure crops, no artificial means of main- taining the humus and nitrogen content of soils need be resorted to. THE USE OF PHOSPHORUS Iowa soils are not abundantly supplied with phosphorus. Moreover, it is impossible by the use of manures, green manures, crop residues, straw, stover, etc., to return to the soil the en- tire amount of that element removed by crops. Crop residues, stover and straw merely re- turn a portion of the phosphorus removed, and while their use is important in checking the loss of the element, they cannot stop it. Green manuring adds no phosphorus that was not used in the growth of the green manure crop. Farm manure returns part of the phosphorus removed by crops which are fed on the farm, but not all of it. While, therefore, immediate scarcity of phosphorus in Iowa soils cannot be positively shown, analyses and results of ex- periments show that in the more or less distant future, phosphorus must be applied or crops will suffer for a lack of this element. Furthermore, there are indications that its use at present would prove profitable in some instances. Phosphorus may be applied to soUs in three commercial forms, bone meal, acid phosphate and rock phosphate. Bone meal cannot be used generally, because of its extremely limited production, so the choice rests between rock phosphate and acid phosphate. Experiments are now under way to show which is more economical for all farmers in the state. Many tests must be conducted on a large variety of soil types, under widely differing conditions, and thru a rather long period of years. It is at present impossible to make these experiments as complete as desirable, owing to small appropriations for such work, but the results secured from the tests now in progi-ess will be published from time to time in the different county re- ports. Until such definite advice can be given for individual soil types, it is urged that farmers who are interested make comparisons of rock phosphate and acid phosphate on their own farms. In this way they can determine at first hand the relative value of the two materials. Information and suggestions regarding the carrying out of such t«sts may be secured upon application to the Soils Section. LIMING Practically all crops grow better on a soil which contains lime, or in other words, on one which is not acid. As soils become acid, crops grow smaller, bacterial activities are reduced and the soil becomes infertile. Crops are differently affected by acidity in the soil; some refuse to grow at all; others grow but poorly. Only in a very few instances can a satisfactory crop be secured in the absence of lime. Therefore, the addition of lime to soils in which it is lacking is an important principle in permanent soil fertility. All soils gradually become acid because of the losses of lime and other basic materials thru leaching and the production of acids in the decomposition processes constantly occurring in soils. Iowa soils are no excep- tion to the general rule, as was shown by the tests of many representative soils reported in bulletin No. 151 of this Station. Particularly are the soils in the lowan drift, Mississippi loess and Southern Iowa loess areas likely to he acid. All Iowa soils should therefore be tested for acidity before the crop is seeded, particularly when legumes, such as alfafa or red clover, are to be grown. Any farmei* may test his own soil and determine its need of lime, according to simple directions given in bulletin 151, re- ferred to above. As to the amount of lime needed for acid soils as a general rule sufficient should be applied to neutralize the acidity in the surface soil and then an additional amount of one to two tons per acre. SOIL AREAS IN IOWA There are five large soil areas in Iowa, the Wisconsin drift, the lowan drift, the Missouri loess, the Mississippi loess and the Southern Iowa loess. These five divisions of the soils of the state are based on the geological forces which brought about the formation of the various soil areas. The various areas are shown in the accompanying map. With the exception of the northeastern part of the state, the whole surface of Iowa was in ages past overrun by great continental ice sheets. These great masses of ice moved slowly over the land, crushing and grinding the rocks beneath and carrying along with them the material which they accumulated in their progress. Five ice sheets invaded Iowa at different geological eras, coming from different directions and carrying, therefore, different rock mate- rial with them. 52 SOIL SUEVEY OF IOWA The deposit, or sheet, of earth debris left after the ice of such glaciers melts is called "glacial till" or "drift" and is easily distinguished by the fact that it is usually a rather stiff clay containing pebbles of all sorts as well as large boulders or "nigger-heads." Two of these drift areas occur in Iowa to-day, the Wisconsin drift and the lowan drift, covering the north central part of the state. The soils of these two drift areas are quite different in chemical composition, due primarily to the different ages of the two ice invasions. The lowan drift soil was laid down at a much earlier period and is somewhat poorer in plant food than the Wisconsin drift soil, having undergone considerable leaching action in tlie time which has elapsed since its formation. The drift deposits in the remainder of the state have been covered by so-called loess soils, vast accumulations of dust-like materials which settled out of the air during a period of geological time when climatic conditions were very different than at present. These loess soils are very porous in spite of their fine texture and they rarely contain large pebbles or stones. They present a strong contrast to the drift soils, which are somewhat heavy in texture and filled with pebbles and stones. The three loess areas in the state, the Missouri, the Mis- sissippi and the Southern Iowa, are distinguished by differences in texture and appearance, and they vary considerably in value for farming purposes. In some sections the loess is very deep, while in other places the underlying leached till or drift soil is very close to the surface. The fertility of these soils and their needs are greatly influenced, therefore, by their depth. It will be seen that the soils of the state may be roughly divided into two classes, drift soils and loess soils, and that further divisions may then be made into various drift and loess soils because of differences in period of formation, characteristics and general composition. More accurate information demands, however, that further divisions be made. The different drift and loess soils contain large numbers of soil types which vary among themselves, and each of these should receive special attention. THE SOIL SURVEY BY COUNTIES It is apparent that a general survey of the soils of the state can gfve only a very general idea of soil conditions. Soils vary so widely in character and composition, depending on many other factors than their source, that definite knowledge concerning their needs can be secured only by thoro and complete study of them in place in small areas. The climatic conditions, Fig. 11. Map showing the principal soil areas in Iowa POTTAWATTAMIP] COUNTY SOILS 53 topograjiliy, depth and cliaiJU't^r of tlie soil, cheinieal and mechanical composition, and in short all the factors which may affect crop production, must be considered. This is what is accomplished by the soil survey of the state by counties, and hence the needs of individual soils, and proper systems of management may be worked out in much greater detail and be much more complete than would V)e possiVde by merely considering the large soil areas separated on tlie basis of their geological origin. In other words, while the unit in tlie general survey is the geological history of the soil area, in the soil survey by coun- ties or any other small area, the unit is the soil type. GENERAL SOIL CHARACTERISTICS Soil types possess more or less definite characteristics which may be determined largely in the field, altho some laboratoiy study is necessary for final disi)Osition. Usually the line of separation Vjetween adjoining soil types is quite distinct and it is a simple matter to locate tlie type Ixjundaries. In some cases, however, there is a gradation from one type to another and then tiie boundaries may be fixed only with great difficulty. The error introduced into the soil sui-\'ey work from this souicc is very small and need cause little concern. The factors which must be tjikeii into account in establishing soil types have Ih'cu well enumerated by tlie Illinois Agricultural Experiment Station in its Soil Report No. 1. They are: 1. The geological origin of the soil, whether residual, glacial, loessial, alluvial, colluvial or cumulose. 2. The topography or lay of the land. .'5. The structure or depth anil character of the surface, subsurface and subsoil. 4. The physical or mechanical composition of different strata composing the soil, as the jiercentages of gravel, sand, silt, clay and organic matter which they contain. 5. The texture or porosity, granulation, friability, plasticity, etc. 6. The color of the strata. 7. The natural drainage. 8. The agricultural value based upon its natural productiveness. 9. Native vegetation. 10. The ultimate chemical composition and reaction. The common soil constituents may be given as follows i according to the Bureau of Soils: Organic Matter \ ^^^ Partially destroyed or undecomposed / vegetable and animal material. Stones — over 32 mm.* Gravel— 32— 2.0 mm. Very coarse sand Coarse Sand — -1.0 — 0..5 mm. Medium Sand — 0..5 — 0.2.5 mm. Fine Sand— 0.25— 0.10 mm. Very fine Sand — 0.10 — 0.0,5 mm. Silt— 0.05— 0.00 mm. SOILS GROUPED BY TYPES The different geueral groujjs of soils by types are indicated thus by the Bureau of soils: 2 Peats — Consisting of 35 per cent or more of organic matter, sometimes mixed with more or less sand or soil. Peaty Loams — 15 to 35 per cent of organic matter mixed with much sand and silt and a little clay. Muds — 25 to 35 per cent of partly decomposed organic matter mixed with much clay and some silt. Clays — Soils with more than 30 per cent clay, usually mixed with much silt ; always more than 50 per cent silt and clay. Silty Clay Loams — 20 to 30 per cent clay and more than 50 per cent silt. Clay Loams — 20 to 30 per cent clay and less than 50 per cent silt and some sand. Silt Loams — 20 per cent clay and more than 50 per cent silt mixed with some sand. Loams — Less than 20 per cent clay and less than 50 per cent silt and from 30 to 50 per cent sand. * 25 mm. equals 1 in. 1 Bur. of Soils Field Book. 2 1 C. Inorganic Matter 54 SOIL SURVEY OF IOWA Sandy Clays — 120 i>er cent silt and snnill amounts of clay up to 30 i)er cent. Fine Sandy Loams — More than 50 ])er cent fine sand and very fine sand mixed with less than 25 per cent very coarse sand, coarse sand and medium stind, much silt and a little clay; silt and clay 20 to 50 per cent. Sandy Loams — More than 25 per cent very coarse, coarse and medium sand; silt and clay 20 to 50 per cent. Very Fine Sand — More tiiaai 50 per cent fine siind ;ind less than 25 per cent very coarse, coarse and medium sand, less than 20 per cent silt and clay. Fine Sand — More than 50 per cent fine sand and less than 25 per cent very coarse, coarse and medium sand, less than 20 per cent silt and clay: Sand — More than 25 per cent very coarse, coarse and medium sand, less than 50 per cent fine sand, less than 20 per cent silt and clay. Coarse Sand — More than 25 {ht cent very coarse, coarse an