599 C2 L37 A A n SOUT 1 JO 2 7 o 4 5 3 RARY FA CILITY ?LisagS£7.fi 6::«Mfi¥W6«taia« RESERVED Soil Surveys Stockton #67 'SOBommmmma sics Library of Cai(((yr^ Los Angeles L 006 467 229 8 I S a C4^'\A.l ^&le oivo the resuks of ineehanieal analyses of typical samples of the Stoekton loam adobe : Mechanical analyses of Siuckton loam adobe. Number. j Description, 1301)1 : Soil 13063 Subsoil Fine Coarse j Medixim Fine Very line cjj^ gravel. sand. sand. sand. ' sand. Per cent. 0.5 .6 Per cent. Per cent.' Per cent.l Per cent. 3.0 3.2 I 15.2 I 21.6 3.0 ' 2.9 15.1 20.6 Clay. Per cent. 30.8 «.3 Per cent. 25.9 14.8 The followins; samples contained more than one-half of 1 per cent of calcium carbonate (CaCOa) : No. laOGl, 1.45 per cent; No. i;i()fi2, 2.18 per cent. STOCKTON CLAY ADOBE. 'J'he Stockton clay adobe consists of a chocolate-brown to nearly black heavy clay adobe, with a depth of about 36 inches, and under- lain to a depth of 6 or more feet by a light-j^ellow subsoil of fine, silty cla}'^ texture. The soil is of close compact structure, polishing Iiighly upon the soil auger, is exceedingly tenacious and of a stiff puttylike consistency when wet, checking at the surface into large blocks by deep surface cracks upon exposure. In advanced stages of checking, the larger blocks are divided and subdivided by smaller checks and cracks, causing the surface to break up on cultivation into a loose mass of small blocks and pellets of the size of small peas and larger. The subsoil is of much less dense and compact structure than the soil, but is very sticky when wet and frequently carries small rounded concretions or incipient hardpan formation. Both soil and subsoil frequently contain small subangular rock particles of the size of fine gravel. The more extensive and typical bodies of the Stockton clay adobe occur near the eastern part of the area, in the vicinity of Elliswortli and Collegeville. Many smaller irregular bodies are, however, scat- tered throughout the eastern half of the survey. The surface is low, nearly level, and without distinctive natural features, except for an occasional growth of valley oak. The soil grades into the adjacent loams and the heavy and dense Stockton clay loam adobe. Owing to unfavorable position and to the dense, heavy nature of the soil, natural drainage is generally deficient during the rainy seasons, farm operations and even travel over the roads being greatly hampered or temporarily suspended. The Stockton clay adobe in the main owes its origin to the distribu- tion over the valley floor of very finely divided rock material, derived from a great variety of rocks and modified by an admixture of ancient Pleistocene sediments. Owing to the, texture and structure of the soil, percolation is arrested and the soil when dry absorbs water very slowly. It is, 22 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1905. however, capable of holding a great amount of water when satur- ated, which is slowly given up under evaporation. Under proper methods of cultivation it is thus able to retain much moisture throughout the dry summer seasons, and to supply the crop needs during prolonged droughts. The soil is also generally free from impervious hardpan or alkali salts in such quantities as to become detrimental to crops. The small light-colored spots noted in the description of the Stockton loam adobe are also of frequent occur- rence in the type under discussion. This soil is not generally w^ell adapted to early vegetables or fruits, or to croj^s requiring a light, well-drained soil. It is best suited to the production of alfalfa, forage crop-^, grain, and grain hay. Dairy- ing and stock raising should be profitable industries where the tramp- ling of the soil in wet seasons by stock can be avoided. Alfalfa, grain hay, and grain are the principal crops now grown, the yields being generally good or relatively heavy in favorable seasons. Vines, tree fruits, and vegetables are grown to a limited extent upon lighter phases of the t3'pe in the district lying northeast of Stockton, with fair yields under careful cultivation and attention. The following table gives the results of mechanical analyses of typical samples of the soil and the subsoil of this type : Mechanical analijsrx of Stockton chty adobe. Number. Description. Fine gravel. Coarse sand. Medium sand. Fine sand. Very fine sand. Silt. Clay. ll^OS^ Soil Per cent. 0.4 Per cent. 1.5 Per cent. 1.6 1.9 Per cent. 7.5 8.1 Per cent. 12.3 13.0 Per cent. 36.4 33.1 Per cent. 40.2 13064 Subsoil .3 1.9 42.3 STOCKTON CLAY LOAM ADOBE. The Stockton clay loam adobe consists of a black clay loam adobe, similar in structure features to the Stockton clay adobe, but of smoother texture, being generally free from coarse or gritty material. It polishes highly upon the soil auger and assumes an exceedingly tenacious, w^axy or stiff, puttylike consistency when wet. During the dry season the checking of the surface is often developed to a re- markable degree. It is underlain at aI)out 8 feet by a yellow heavy silt}^ or silty clay subsoil, becoming lighter in the lower part of the section and similar to that of. the Stockton clay adobe. The surface of the subsoil in the more southerly lying bodies is frequently some- what comj)acted and j^artially cemented immediately below the over- lying soil into a soft, iuiperfect hardpan or separated from the over- lying soil by a thin white crust of relatively soft, calcareous hardpan. The Stockton clay loam adobe is one of the most important soils of the area, occurring in the most extensive and typfcal bodies to the SOIL SURVEY OF THE STOCKTON AREA, CALIFORNIA. 23 north, south, and east of Stockton. The surface is h)w, level, and without topographic variety. An occasional grove of valley oak appears, but much less frequently than upon the adjacent soils of lighter texture and more open structure. As in the Stockton clay adolie, the natural drainage is poor, the soil becoming uncultivable during wet seasons. The mode of formation of this soil is somewhat obscure. The materials constituting it are probably derived from a great variety of rocks, and have been dis- tributed by the waters of streams and tides and modified by the incorporation and decomposition of vegetable matter. It is gener- ally free from alkali salts in injurious quantities, and in its pro- nounced moisture-retaining properties is very similar to the Stock- ton clay adobe. Like the Stockton clay adobe also, it is best adapted to alfalfa, grass and forage crops, and grains, which crops are at present the principal ones grown. The yields are generally good, unless proper preparation of the land is prevented by unfavorable weather and drainage conditions, or the growth of the crop is retarded by the rav- ages of fungous diseases or insect pests, the development of rust or other fungus sometimes being induced by the wet conditions in the low-lying areas. The following table gives the average results of mechanical analy- ses of typical samples of the soil and the subsoil of this type : Mecltanicdl (niali/scs of Stockton vJay Joani adobe. Number. Description. Fine gravel. Coarse sand. Medium sand. Fine sand. Very fine sand. Silt. Clay. 13066. Soil Subsoil Per cent. 0.5 .5 Per cent. 1.3 1.6 Per cent. 2.0 2.1 Per cent. 12.3 17.1 Per cent. 17.9 20.3 Per cent. 35.0 34.4 Per cent. 30.9 13067,13068 2,3.7 SACRAMENTO CLAY LOAM. The Sacramento clay loam occurs typically as a dark-colored, nearly black heavy silty clay loam, containing a large proportion of organic matter, the remains of decaying vegetation. The soil generally extends to the depth of about 30 inches. The proportion of organic matter is usually, but not always, less in the first few inches than in the lower part of the soil section. Vegetable fiber is of frequent occurrence, but the greater part of the organic matter is thoroughly decomposed. The dark-colored soil is underlain by a light-yellow fine silty loam, frequently grading into a very fine sandy loam, and extending to the depth of O or more feet. Both soil and subsoil are free from gravel or other coarse material, of somewhat compact struc- ture, sticky when wet, but friable under cultivation. 24 fip:ld ()Pp:rations of the bureau of soils, lOOo. The type is subject to considerable variation in depth, texture, char- acter of subsoil, and in the relative amounts of silt and organic mat- ter. In the vicinity of the adjacent peat lands it is underlain by the partially decomposed peat instead of by the yellow silty loam sub- soil, as described. A silty clay phase also occurs in a few small areas in the vicinity of the San Joaquin River and some of its larger tribu- taries. This phase consists of a deposit of from a few inches to 2 feet or more of a light yellow, very fine, heavy silty or silty clay loam, very sticky when wet, and of rather compact, dense structure, imder- lain by the peaty and silty loam materials of the typical soil. It is similar to the typical soil in most other particulars, but is of a more refractory, denser texture and structure and requires more careful preparation and cultivation. The Sacramento clay loam is an extensive and important soil type, occurring in the central and southwestern parts of the area. The sur- face is generally level or only slightly inclined, and treeless, except in the vicinity of the streams. The depressions, which are of defi- cient drainage, are usually marked by a growth of tules or rushes. The soil jjasses gradually into the adjacent peat lands, adobes, and loams. f Percolation is sometimes retarded by the compact structure of the subsoil, which, with the low-lying position and gentle slope, often results in insufficient natural drainage, and open drainage ditches are frequently encountered in the cultivated areas of this type. The Sacramento clay loam owes its origin to the admixture of the fine river silts, derived from a variety of rocks and distributed by the San Joaquin River and its tributaries and branches, with the fine alluvial and decomposed organic matter of the tidal fresh-w^ater marshes or peat lands. The material from these two sources is either intimately mixed or deposited in alternating strata. The soil is gen- erally free from alkali salts in injurious quantities, and under proper cultivation possesses valuable moisture-retaining properties. While containing a large amount of organic plant food, and gen- erally productive, the crop yields decline where a single crop is grown continuously. When the water ta})le is not too close to the surface, the type is best adapted to alfalfa, to grass and forage crops — such as redtop, rye grass, timothy, some of the clovers — and to root crops, beans, vegetables, and grain. Much of this land is admirably adapted- to dairying and stock raising. Small and tree fruits, consisting of peaches, apricots, pears, and cherries, also do well in the higher and better drained areas of lighter texture. (irain hay and grain, consisting of wheat, barley, and oats, are the principal crops, the yields being usually good. Alfalfa, in connection Avitli dairying and stock raising, is also grown in limited (juantities. In small, fa\()ral)ly situated Ixxlies. esj>ccialh^ in the vicinity of the SOIL SURVEY OF THE STOCKTON AREA, CALIFORNIA. 25 San Joaquin River, fruit and vegetable production is of considerable importance and profit. The following table gives the results of mechanical analyses of typical samples of the soil and subsoil of this type : Mechanical analyses of Sacramento clay loam. Number. Description. Fine Coarse Medium Fine Very fine gravel. ' sand. sand. sand. sand. Silt. Clay. v.mi Soil Per cent. 0.3 Per cent. 0.8 .8 Per cent. 0.5 .4 Per cent. 2.5 9.0 Per ce7it. 6.3 36.2 Per cent. 40.3 46.5 Per cent. 49.7 13(>->8 Subsoil .5 16.6 The following sample contained more than one-half of 1 per cent of calcium carbonate (CaCOa) : No. 13058, 1.36 per cent. In point of extent of area covered, naturally unproductive condi- tion, progress of reclamation operations, and agi'icultural possibili- ties, the Peat lands of the Stockton area are of great interest and importance. In typical section the soil consists of 6 feet or more of fine alluvial river and tidal silts, intimately commingled with partially decayed vegetable matter, undecomposed plant roots, stems, and fibers occur- ring in great profusion.. This material is dark brown to black, of an exceedingly smooth and pasty consistency when wet, of spongy tex- ture, and generally saturated with water at a depth of 2 or 3 feet or less. In certain districts subjected to recent overflow by streams in flood, the surface foot frequently consists largely of river silts, in which the usual proportion of organic matter is greatly decreased. The subsoil is, however, the same. The depth of the Peat is also subject to considerable variation, usuallj^ increasing in the direction of the lower San Joaquin River, which leaves the area near the northwestern extremity. Near the margins of the soil bodies it is frequently underlain at a depth of from 4 to G feet by a stratum of sa nd3;^ la y of bluish cast,^ - by com- pact river silts and fine sands, though a\'er the greater proportion of theTsoil areaflie iiiulerlying light-colored fine river sands are encoun- tered only at a depth of from 10 to 15 feet or more, while in the north- western portion of the area the depth of the peaty deposits is much greater. In parts of this latter mentioned section only the immediate crust is of sufficient solidity and toughness to bear the weight of farm animals or machinery, the underlying material being in an exceed- ingly soft semifluid condition, and extending to great depths. Although quite sticky when wet, there is but little or no tendency toward puddling, the surface being friable and easily cultivated after the first breaking or cutting away of the surface accumulation of the II 26 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1905. tough roots of aquatic plants. No gravel or other coarse material appears in either soil or subsoil. This important soil type occurs only in the San Joaquin River delta region, where it covers the greater proportion of the entire western half of the area surveyed. The topographic and drainage features, min- eralogical origin, and mode of formation are much the same as in the other soils of the lower delta. The drainage conditions will be dis- cussed more particularly under the succeeding heading. Extreme lightness in weight constitutes a very striking feature of the Peat, large fragments frequently becoming detached and floating about with the stream and tidal currents. The soil carries a great supply of plant food and under favorable conditions yields enormously. This has given rise to the belief that the soil is capable of continuousl}^ producing all manner of crops, without regard to the principles of ordinary farm management or crop rotation. This belief is not borne out by agricultural practice. "While ranking among the most productive soils known and while maintaining this productiveness, when farmed under ordinary, care- ful, modern methods, the long-continued growing of successive crops of grain, as in the case of other soils, is resulting in decreased pro- duction. \^he profitable growing of successive crops of potatoes is said to DC limited to three or four years. L' The accidental ignition of the Peat from " tule fires," or in other ^ways, often proves troublesome, the organic material of the soil slowly smoldering until practically removed, unless the fire ^e checked by flooding. This leaves the soil a mere bed of red or light- colored ash, and greatly reduces its value, and, moreover, increases capillary movement and rapid evaporation from the surface, resulting frequently in the surface accumulation of alkali salts in injurious quantities. T^Hien not modified by ignition, the capillary or upward movement of soil waters takes place so slowly that the application of irrigation waters to the soil surface frequently becomes necessary during the dry season, although the soil may be saturated with water at the depth of 3 or 4 feet, or even less. While alkali salts exist in these soils and in the surface waters in considerable amounts, under ordinary conditions they are not of suf- ficent concentration to become injurious to ordinary crops, and their accumulation in harmful quantities takes place only through the destruction of the natural, coarse, mulchlike structure of the soil. The Peat is generally ill adapted to the growing of alfalfa or other deep-rooted crops, owing to the close approach to the surface of the water table. On the other hand, it is admirably adapted to certain I special crops, such as asparagus, beans, onions, or other vegetables, / forage crops, timothy, redtop, ryegrass, some of the clovers, and to /' potatoes or grain. The risk of damage to crops and lands from fires SOIL SURVEY OF THE STOCKTON AREA, CALIFORNIA. 27 caused by steam harvesters is, however, of some importance in grain ])roduction. Harvesting is also sometimes interfered with by the wet condition of the hinds, resulting from high water and imi)erfect levee or drainage systems. In the older reclaimed districts and in those not devoted to special crops this soil is especially adajited to the growing of hay and forage crops in connection with dairying and stock raising. Of the foregoing crops grain, jwtatoes, beans, asparagus, onions, and other vegetables are the principal products. Dairying is also an nnportant interest. Alfalfa is successfully grown upon some of the earlier reclaimed and better drained tracts. In newly reclaimed districts crops are sometimes uncertain for the first one or two seasons, owing to imperfections and delay in establishing proper drainage conditions. Considerable risk and expense always attend the prac- tice of agriculture upon this soil type, but, with the exceptions noted, the yields and profits during favorable seasons are usually so great as to offset occasional losses. SPECIAL SOIL PROBLEMS. The occurrence of a hardpan formation witliin the limit of the root zone of crops is of great importance in its bearing upon percolation, drainage, the conservation of soil moisture, and direct effect upon plant growth. Not only is the root zone of crops greatly limited by the occurrence of impenetrable hardpan strata lying near the soil surface, but cultivation is frequently interrupted, the movement of soil water arrested, drainage retarded, and the power to retain and to deliver moisture decreased. Lands in w^liich this hardpan occurs usually become dry during periods of drought or dry seasons, and if irrigated, frequently become Avaterlogged, crops thus suffering from the extremes of moisture condition. In the Stockton area hardpan is of frequent or of general occur- rence in a few of the soil types. It is, however, subject to great varia- tion in structure and in its effects uj)on agriculture. The most pronounced hardpan is found in the San Joaquin loam and the San Joaquin sandy loam, lying along the eastern margin of the sheet. It is generally of light-red color, fine texture, save for an occasional inclusion of gravel, and dense structure, impenetrable to the soil auger or to the roots of plants. It usually occurs at a depth of from but a few inches to 3 feet and is frequently exposed at the surface by slight erosion. It does not soften upon application of water, and when exposed to the air weathers very slowly. It is of secondary formation, resulting from physical and chemical changes that take place in the soil and cause the cementing of the material into a dense, impenetrable mass. The red color is produced by the iron salts present in the soil, and this mineral is doubtless instrumental in the formation of the hardpan. 28 FIELD OPERATIONS OF THE BUREAU OF SOILS, 1905. Throughout the eastern-central part of the area a much less in- tractable and therefore less injurious hardpan occurs. It is found within the zone of ordinary root development only in the case of some of the lower lying, heavy adobe soils, and amounts merely to j^artial cementation of the underlying heavy loam subsoil by lime carbonate. A thin whit^ crust of true lime carbonate hardpan of quite dense structure frequently separates the soil and subsoil. Both this crust and the Underlying compact and partially cemented subsoil are j^enetrated by the soil auger and j^robably frequently by the roots of trees and field plants. It lies uniformly at a lower depth than the hardpan first described, which is another reason why it is much less injurious in its effects upon crops. The white hardpan of the Fresno fine sandy loam occurring in the southern and eastern parts of the area is, however, of a more dense and firm character and of greater importance in its influence upon growing crops. This material consists of a firm white stratum, usually only a few.jnches in thickness, of fine texture, and ashy con- sistency when pulterized. It softens slowly upon application of water. Several of these strata may occur separated by the uncon- solidated soil. Much of the fine ashy material is probably of vol- canic origin, rich in alkali salts, and consolidated by lime and alkali carbonates. It does not approach the surface so closely as to inter- fere with plowing or other cultivation, and is much less extensive, uniform, and continuous than the red hardpan found in the eastern part of the area. It is of importance mainly as being the seat of much of the injurious alkali salts of this district and in its effect of retarding the removal of such salts by the drainage water. A^Hiile no areas occur in the Stockton area that may be properly designated as '' worn-out " lands, the productiveness of certain soils of the valley and delta has been decreased by continued cropping to grain or other crops. In such cases, a more careful system of culture, the rotation of crops, the production of fat stock and farm animals, and the practice of a more diversified system of farming are to be recommended where consistent with location and with climatic and soil conditions. The improvement of the areas of " burned-out " Peat is also a matter of importance. Careful management is necessary to bring these patches to their former state of productivity. The addition of coarse animal and vegetable manures and the culture of clovers, forage crops, and the practice of green manuring is recommended. RECLAMATION OF SWAMP LANDS. It is to modern engineering skill in the erection of levees and the drainage of the delta or swamp lands covering the most of the western portion of the Stockton area that this extensive district owes its agricultural importance. Lying but a few feet above low-tide SOIL SURVEY OF THE STOCKTON AREA, CALIFORNIA. 29 level, these island tracts, as previously noted, are thickly covered with a dense <>rowth of the round tule {Srirpits hieiisfrf's). This aquatic reed, dyin. :w >^^ i ms/'-.m