UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA AN INDEX FOR RATING THE AGRICULTURAL VALUE OF SOILS R. EARL STORIE BULLETIN 556 SEPTEMBER, 1933 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Introduction 3 Method of rating 5 Factor A: character of soil profile 5 Group I, unweathered or only slightly weathered secondary soils (recent or young soils) 6 Group II, moderately weathered secondary soils (immature secondary soils) 13 Group III, strongly weathered secondary soils with dense clay subsoils (semimature secondary soils) 14 Group IV, maturely weathered secondary soils with hardpan 15 Group V, strongly weathered soils with dense clay subsoils resting on con- solidated materials 17 Group VI, soils developed on bedrock (primary or residual soils) ... 19 Factor B : texture of surface soil . • 21 Medium-textured soils 24 Medium-heavy-textured soils 25 Heavy-textured soils 25 Light-textured soils 26 Gravelly or cobbly soils 27 Stony soils 27 Factor C: soil-modifying conditions 28 Drainage 28 Alkali 28 Acidity 30 Infertility 30 Stratified subsoils (gravelly layers or stratified clay layers) 31 Shallow phases of alluvial soils 31 Eroded soils 31 Steep phases 32 Nonagricultural materials 32 Calculation of the index 34 Soil rating for a tract of land 35 Summary 39 Acknowledgments 39 List of selected references 40 Appendix: soil survey data in California 41 AN INDEX FOR RATING THE AGRICULTURAL VALUE OF SOILS 1 E. EARL STORIE 2 INTRODUCTION The growth and production of plants is dependent very largely upon the soil, and particularly the degree to which it presents conditions favorable for the extension and development of plant roots. On soil that is deep, pervious, relatively uniform in character, and that has fair water-retaining capacity, a very wide range of plants may grow vigor- ously. On soil with subsoil characteristics that retard the extension of plant roots, growth and development of the plants may likewise be retarded. If the subsoil is only moderately dense and root development only slightly hindered, the growth and production may be good, but if the density of the subsoil reaches that of a claypan, root penetration may be decidedly limited, and if the subsoil is cemented into a true hardpan, or underlaid by hard bedrock, penetration is definitely pre- vented. These variations in the character of the soil are directly related to its origin, its mode of formation, and the age or stage of weathering. Recent alluvial deposits are generally deep and pervious, and the profile, or vertical section through the soil mass, shows no variations such as are developed with age. Older soils, which have been exposed to the weather- ing agents for very long periods of time, have subsoils that have become more dense, until finally they may reach the claypan or hardpan stage. Such soils, which are considered maturely weathered, have approached a condition of equilibrium with the factors that have determined the particular characteristics of their profiles. The growth of plants on the soil is so closely related to these char- acteristics of the profile, and the chemical composition of the several horizons of the soil is likewise so closely related to the profile, that it appears possible to rate the soils with the profile characteristics as a base. i Received for publication April 25, 1933. 2 Assistant Soil Technologist in the Experiment Station. [3] 4 University of California — Experiment Station The index for rating soils as used herein is a numerical expression of the degree to which a particular soil presents conditions favorable for plant growth and crop production under good environmental condi- tions. In arriving at the relative index of soils three general factors are considered. These are (A) the character of the soil profile; (B) soil tex- ture; and (C) other modifying factors, such as drainage, alkali, and other miscellaneous conditions. Each of these three factors is evaluated on the basis of 100 per cent for the most favorable or ideal condition, with limiting maximum and minimum ratings ascribed to conditions that are less favorable for plant growth. The information set forth in the various soil-survey publications has been used in developing the index. For a discussion of the soil survey as a source of information, the reader is referred to the Appendix. In studying, mapping, and classifying soils, the character and degree of development of the soil profile, the reaction of the soil mass, the color, the physical composition of the various horizons, the mode of formation and composition of the parent material, the drainage and surface relief, the alkali content, natural cover, etc., are considered in detail. In arriving at the ratings the experience and judgment of the men engaged in soil-survey work in California has been called upon, and the ratings express the results of their collective studies of the relations of these several conditions of the soil to the growth and production of plants. Obviously, such ratings cannot be final and infallible and may be changed as experience with the use of the soil index indicates. The index is based on soil conditions alone independent of other physical or economic factors which might determine the desirability of growing certain plants in a given location ; hence it cannot be regarded as by itself an index for land evaluation. In the latter, other factors, such as variations in climate, availability of water for irrigation, facili- ties for transportation and markets, social conditions, and the like, must be included. Although the soil is only one of the many factors that determine the value of any given area of land surface, it is one that does not readily change and that cannot be materially modified without the expenditure of much effort. Its quality or value is one of the more stable elements that determine land value, and an index for rating soils should serve to simplify the work of land classification and evaluation. Other factors, such as the climate, or the quality, quantity, and availability of water for irrigation are likewise natural factors, more or less stable in char- acter, that may be rated in a similar manner, but some physical, eco- nomic, and social factors may be too variable or too readily changed to permit of such treatment. Studies of these other factors that influence Bul. 556] Index for Rating Value of Soils 5 or modify land values may show the possibilities of developing indexes for groups of these factors, and by integrating these several indexes, a positive numerical expression of the relative value of any portion of the land surface may result. METHOD OF RATING In most endeavors to rate soils on a comparative basis the "score card" method has been used, and the rating determined by adding the points credited to each of the soil characteristics or modifying factors. In the index method here presented the rating is obtained by multiplying the three factors, A times B times C, thus permitting any one of these to dominate or control the final rating. As an example, a soil may have an excellent profile condition warranting a rating of 100 per cent for factor A, excellent surface-soil conditions giving 100 per cent for factor B, but a bad alkali accumulation that would give a rating of 10 per cent for factor C. Multiplying these three percentage ratings — A x B x C — gives 10 per cent as the index for this soil. The severe alkali accumulation would dominate the quality of this soil, rendering it wholly unproduc- tive for plants and would justify the index of 10 for that soil. On the score-card basis, with possibly 20 or 25 points ascribed to alkali or simi- lar conditions, its worst rating could be only 75 or 80. The characteristics or conditions included under each of these factors is described in the following chapter, and their bearing on the quality of the soil is discussed. FACTOR A : CHARACTER OF SOIL PROFILE Factor A evaluates all the characteristics of the soil profile except the texture of the surface soils. These characteristics, which are determined by the kind of parent material, its mode of formation or accumulation, and the age or degree of modification of the soil material by the weather- ing agencies of climate, supplemented by vegetation and opposed by erosion and deposition, serve to separate the soils into groups of related individuals that are classed as soil series. The suitability of soils for plant growth is dependent to a very large extent on the profile characteristics that differentiate the soil series. A series may be defined as "a group of soils having the same character of profile ; that is, the same range in color, structure, and general sequence of soil and subsoil horizons, the same general types of relief and drain- age, and a common or similar origin and mode of formation." 3 The 3 Shaw, C. F. A glossary of soil terms. American Soil Survey Association Bul. 9:28-58. 1927. 6 University of California — Experiment Station name of the series implies all the characteristics used to define the soil type except that of surface texture. For factor A of this index, the soil series of California have been placed in six general groups and a rating given soils of these groups. In each group are series having similar modes of formation, similar sequence of soil and subsoil horizons (i. e., layers), a comparable age, and the same types of relief. The soil series of California officially rec- ognized by the Bureau of Chemistry and Soils of the United States Department of Agriculture and the California Agricultural Experi- ment Station are listed alphabetically in table 1 with their position in the six groups on the basis of factor A and with certain of their profile characteristics indicated. The profile characteristics and inclusive ratings for each group under factor A are given in table 2. Secondary 4 soils are placed in groups I, II, III, and IV; strongly weathered secondary and primary 5 soils having dense clay subsoils de- veloped on consolidated material in group V; and primary soils in group VI. In the following sections characteristics of the soils in each group are described and the profile rating of each explained. Where soil surveys have been made, the necessary information for this grouping can be obtained from the reports and maps, but if a survey has not been made, then a field examination of the area to be rated is needed in order to determine the profile characteristics. GROUP I, UNWEATHERED OR ONLY SLIGHTLY WEATHERED SECONDARY SOILS (RECENT OR YOUNG SOILS) When they have been transported by water, the unweathered second- ary soils are commonly referred to as the alluvial, stream-bottom, flood- plain, alluvial-fan, or recent, transported soils. Group I also includes soils deposited or reworked by the action of winds, commonly classed as aeolian or wind-modified soils. Soils of this group are characteristically more than 6 feet deep and consist of a mass of soil material which has not been modified to any extent by the action of weathering forces, which ultimately bring about a change in the general character of the soil profile. It is because of this that they are spoken of as unweathered soils, in contrast to the moder- ately weathered soils of group II. 4 Secondary soils are those formed by the accumulation and weathering of transported materials, originating from previously existing soils and from rock debris, and are often referred to as alluvial, aeolian, or glacial soils, according to the agency which transported them. s Primary soils are those formed by the disintegration and decomposition of rocks in place and the weathering of the resultant debris to true soil. Bul. 556] Index for Rating Value of Soils TABLE 1 Soil Series of California Listed Alphabetically Showing Their Positions in the Six Groups on the Basis of Factor A, and also Showing the Color* of the Surface Soil and the Soil Beaction Series Adelanto Agate Agueda Aiken Alamo Aliso Altamont Alviso Anderson Anita Antelope Antioch Arbuckle Arnold Arroyo Seco Ataseadero Ayar Ballard Barron Bayside Baywood Bear Belle vista Bieber Bishop Botella Bunting ville ... Butte Cachuma Cajon Canby Capay Carlsbad Carrizo Carson Cayucos Centerville Chamise Chino Chualar Churchill Clear Lake Climax Coachella Cole Columbia Commatti Conejo Contra Costa... Group Color of surface soil Grayish brown Brown Dark brownish gray Red Dark gray Reddish brown Brown Dark gray Yellowish brown Dark brown Dark gray Dark brown Grayish brown Brownish gray Light brown Dark brownish gray Brown Brown Grayish brown Grayish brown Dark brown Reddish brown Light gray Dark brown Dark brownish gray Dark brownish gray Dark grayish brown Brownish gray Reddish brown Light brownish gray Light gray Dark grayish brown Brown Light gray Dark gray Dark gray to black Chocolate brown Dark grayish brown Dark gray Dark brown Grayish brown Dark gray to black Dark gray to black Gray Dark grayish brown Light grayish brown Gray Dark gray to black Reddish brown General reaction III V I VI IV III VI I I II V III I VI I V VI II II I I I IV V I I II VI III I V III VI I I VI III V II II IV I VI I II I II I VI Calcareous subsoils Calcareous substratum Calcareous throughout Moderately acid Neutral Calcareous subsoils Calcareous subsoils Usually saline Neutral Neutral Neutral Calcareous subsoils Neutral Moderately acid Neutral Slightly acid Calcareous throughout Neutral Neutral Moderately acid Moderately acid Neutral Calcareous throughout Neutral Calcareous throughout Neutral Calcareous subsoils Neutral Neutral Calcareous throughout Calcareous subsoils Calcareous subsoils Slightly acid Calcareous throughout Calcareous subsoils Moderately acid.. Calcareous subsoils Moderately acid Calcareous subsoils Neutral Calcareous throughout Calcareous subsoils Neutral Calcareous throughout Slightly acid Neutral Calcareous subsoils Neutral Neutral * Color, one of the most obvious of the many soil characteristics, is so closely correlated with the condi- tions under which the soil has been formed that it often gives considerable information concerning the other characteristics of the soil, such as the organic matter content. University of California — Experiment Station TABLE 1— (Continued) Series Group Color of surface soil General reaction Coquille Corning Corralitos Cuyama Danville Daulton Delaney Delano Delhi Denverton Diablo Diamond Springs Docas Domino Dublin Ducor Dunnigan Egbert Elder Elkhorn Elna Empire Encina Escondido Esparto Exeter Fallbrook Fancher Farwell Feather Ferndale Foster Fresno Fullerton Galveston Gleason Garey Gazelle Gila Gloria Goldridge Gould Greenfield Gridley Hames Hanford Hartley Hesperia Holccmb Holland Holtville Honcut Hovey Huerhuero Hugo Imperial Indio I III II II I VI I II I III VI VI II IV I II III I I II IV III VI VI II III VI IV I I I I rv ii i VI ii IV i IV VI V I III III I III I III VI I I II III VI I I Grayish brown, mottled.. Light red Brown Brownish gray Dark brown Reddish brown Light brownish gray Light reddish brown Light brown Dark brown Dark gray to black Grayish yellow Brownish gray Light brownish gray Dark gray to black Dark chocolate brown Brownish gray Dark gray Dark brownish gray Brown Light gray Reddish brown Dark brown Yellowish brown Light brown Reddish brown Reddish brown Reddish brown Light chocolate brown Brown Brownish gray Dark brownish gray Brownish gray Brown Dark gray Dark brown '. Light reddish brown Dark brownish gray Light purplish brown Brownish red Yellowish gray Reddish brown Brown Brown Brown Light brown Light brownish red Light brown Light brown Brown Light purplish gray Reddish brown Dark gray to black Light grayish brown Yellowish brown Light purplish gray Brownish gray Acid; saline Neutral Slightly acid Calcareous throughout Neutral Neutral Neutral Calcareous subsoils Neutral Calcareous subsoils Calcareous subsoils Slightly acid Calcareous throughout Calcareous throughout Neutral Calcareous subsoils Calcareous subsoils Moderately acid Calcareous subsoils Slightly acid Calcareous throughout Strongly acid Slightly acid Neutral Slightly acid Neutral Neutral Neutral Calcareous subsoils Neutral Moderately acid Calcareous throughout Calcareous; alkaline Neutral Usually saline Neutral Moderately acid Calcareous throughout Calcareous throughout Neutral Moderately acid Neutral Neutral Neutral Slightly acid Neutral Neutral Calcareous subsoils Moderately acid Slightly acid Calcareous throughout Neutral Calcareous subsoils Calcareous subsoils Moderately acid Calcareous, alkaline Calcareous throughout Bul. 556 Index for Rating Value of Soils TABLE 1— (Continued) Series Group Color of surface soil General reaction Johnsonville Reefers Rettleman Rimball Rirkwood Rlamath Rneeland Ronokti Laguna Lahontan Landlow Las Flores Las Posas Lewis Lindsey Linne Liver more Lockwood Los Angeles Los Osos Lynndyl Madera Manzanita . . Marcuse Maricopa Marina Mariposa Marvin Marys ville . . May wood McClusky Media Melbourne . Meloland Merced Merriam Metz Mocho Modoc Mojave Mono Monserate. .. Montague Monterey Montezuma Moro Cojo Nacimiento Niland Nord Norman Oakdale Oakley Ojai Olcott Olivenhain.... Olympic II III VI III III III V VI I II V V VI VI III II VI II III VI VI II IV III III II I VI II IV I III VI VI I III III I I II III IV V rv VI in VI VI II I III I I III III V VI Brown Brownish red Gray Brownish red Dark gray Dark gray Dark grayish brown Brown Light brownish gray ... Light gray Brown to dark brown Light gray Brownish red Dark brown Brownish gray.... Dark gray Dark brownish gray Dark grayish brown Grayish brown Light brown Dark brown Light grayish brown... Brown Brownish red Dark gray Reddish brown Brown Brownish yellow Light brown Reddish brown Yellowish brown Dark grayish brown Brown Brown Light brownish gray.... Dark gray to black Light reddish brown. . Light brown Brown Dark brown Reddish brown Light brownish gray... Brown Dark grayish brown Reddish brown Dark gray to black Reddish brown Brownish gray Light brownish gray... Grayish brown Dark brown Grayish brown Light brown Pale yellow Brown Light brown Dark brown Calcareous subsoils Slightly acid Calcareous throughout Neutral Neutral Neutral Moderately acid Slightly acid Neutral Calcareous; alkaline Calcareous subsoils Slightly acid Neutral Calcareous subsoils Usually alkaline Calcareous subsoils Calcareous throughout Neutral Neutral Calcareous subsoils Moderately acid Calcareous throughout Neutral Moderately acid Usually alkaline Neutral Slightly acid Moderately acid Calcareous subsoils Neutral Neutral Moderately acid Neutral Moderately acid Calcareous throughout Calcareous subsoils Calcareous subsoils Calcareous throughout Calcareous throughout Neutral Calcareous throughout Calcareous throughout Calcareous subsoils Calcareous subsoils Moderately acid Calcareous subsoils Moderately acid Calcareous throughout Calcareous; alkaline Calcareous throughout Often alkaline Neutral Slightly acid Neutral Neutral Slightly acid Moderately acid 10 University of California — Experiment Station TABLE 1— (Continued) Series Orland Oxnard Pajaro Panoche Pentz Pinole Pit Placentia Pleasanton Pond Poplar Porterville Preston Ramada Ramona Redding Rhonerville Rincon Rocklyn Rosamond Rositas Sacramento Salinas Salsipuedes San Gabriel San Joaquin San Marcos San Ysidro Santa Cruz Santa Lucia Santa Rita Santa Ynez Santiago Shasta Shedd Sheridan Sierra Siskiyou Sites Solano Soledad Sorrento Stacy Standish Stockpen Stockton Sunol Sunrise Superstition Surprise Sutter Tangair Tassajero Tehama Tierra Tijeras Tujunga Group II I I I VI III I III II II II II I I II IV II II IV II I II II II I IV II II VI VI II III II II VI VI VI VI VI III II I I V III V II IV I I I IV I II V V I Color of surface soil Light grayish brown Brown Brown Brownish gray Dark grayish brown Yellowish brown Dark gray to black Brownish red Brown Brownish gray Light brown Chocolate brown Light grayish brown Light yellowish brown Reddish brown Brownish red Dark brownish gray Brown Brownish red Light grayish brown Light brownish gray Dark gray to black Dark brownish gray Dark brown Light brown Brownish red Dark brownish gray Brownish gray Reddish brown Dark grayish brown Grayish brown Dark grayish brown Dark gray Light brownish gray Gray Dark gray Brownish red Brownish gray Brownish red Dark brownish gray Brown Light brown Light brown Grayish brown Light gray Dark gray to black Reddish brown Light reddish brown Gray Dark brown Light brownish gray Brownish gray Brown Light yellowish brown Dark grayish brown Light reddish brown Light brownish gray General reaction Neutral Calcareous subsoils Neutral Calcareous throughout Neutral Neutral Neutral Neutral Neutral Calcareous; alkaline Neutral Calcareous subsoils Slightly calcareous Neutral Neutral Strongly acid Strongly acid Neutral Slightly acid Calcareous throughout Calcareous throughout Slightly calcareous subsoils Calcareous subsoils Slightly acid Neutral Slightly acid Calcareous subsoils Neutral Moderately acid Neutral Calcareous throughout Neutral Calcareous subsoils Neutral Calcareous throughout Neutral Moderately acid Neutral Moderately acid Calcareous subsoils Neutral Calcareous subsoils Calcareous throughout Calcareous throughout Calcareous subsoils Calcareous subsoils Neutral Calcareous throughout Calcareous throughout Neutral Neutral Moderately acid Neutral Neutral Moderately acid Calcareous throughout Neutral Bul. 556] Index for Rating Value of Soils 11 TABLE 1— (Concluded) Series Group Color of surface soil General reaction Tulare II V V VI VI I VI I VI II VI II I I II I VI VI Vista Strongly acid Dark brownish gray wants Yolo Dark gray to black TABLE 2 Eating of Soils on the Basis of Profile Characteristics Group Group number Description Surface relief Profile rating (factor A) in per cent Unweathered or slightly weathered secondary I Loose and friable material 6 feet or more deep Flat or gently slop- ing 95-100 Moderately weathered sec- ondary soils II Deep but have compact sub- soils and slight to moderate accumulation of clay Terraces, benches or valley floors 80-95 Strongly weathered sec- ondary soils III Dense clay subsoils, loose un- consolidated parent mate- rial Terraces 40-80 Maturely weathered sec- ondary soils IV Hardpan soils, often have fairly dense clay subsoils Flat terraces, valley floors, often hog- wallow surface 5-60 Strongly weathered soils having dense clay sub- soils, developed on con- solidated material V Coastal plain soils High eroded ter- races 20-40 Primary soils (residual) VI Formed in place from decom- position and disintegration of underlying bedrock Hilly, rolling or mountainous 20-70 12 University of California — Experiment Station The most valuable agricultural soils of California fall in this group ; they occur on the flood plains and alluvial fans of many of the California streams. They are especially valuable for orchards, vegetables, and deep- rooted field crops. Yields on many of the medium-textured alluvial soils have remained consistently high for a long period without recourse to fertilization. The crop yields are consistently higher than on soils of the other groups. These soils, providing conditions favorable for the growth of almost any crop plants, have been given a factor-A rating of 95 to 100 per cent. TYPE }^^ -^^-^-^^tX C^^^y LOCATION _ £? l *_"7~~*: ^^^^^HL^i^f^.^t^Z. relief _ BPh^J^l _ elevation § -4^L drainage _>y>i£_ hyo^X, RAINFALL _ 18. i?«J*^L NATIVE VE6ETATI0N _ Q^-^a^^O- _ _ USE _ 'M r '=d^.' u £^. _ _ ORIGIN ^f^^^jk^^r^^ DEVELOPMENT Or PROFILE _ 1&-S*"*- jf»*£-^_ _ _ _ _ REMARKS f~rt-o-l£-C< /coJTj^va fZ ItrO . PROFILE COLOR TEXTURE STRUCTURE CONSISTENCE AND DENSITY REACTION MISCELLANEOUS ROOTS, STONES, CONCRETIONS, PERMEABILITY, ETC. -. *?Z$ <XH.VrTuuJLaJl~- n.o 12- 24- £J± &Jlu(&KtJU44_ ^.Jk 7.o -*V /uxrU. <x»JL 36- 48- 60- Fig. 1. — Soil description and profile of Yolo fine sandy loam. This type of form is of use in reporting and showing tire characteristics of a soil by horizons. Variation in texture of the surface soils is rated under factor B and discussed in a separate section. Any conditions unfavorable to plant growth, such as gravelly subsoil layers, injurious amounts of alkali, high acidity, or poor drainage conditions that may occur are rated under factor C. The Hanford, Yolo, Columbia, and Honcut are extensively developed soil series of this group. The fact that some of the best crop yields of the state are secured on these soils indicates the soundness of the high rating given them. Figure 1 gives a typical profile of a Yolo fine sandy loam which serves to illustrate the general depth and pervious nature of the profiles of soils in group I. Bul. 556] Index for Rating Value of Soils 13 GROUP II, MODERATELY WEATHERED SECONDARY SOILS (IMMATURE SECONDARY SOILS) Group II consists of water-laid or wind-laid deposits which have been subjected to weathering for a sufficient period to develop subsoil char- acteristics very distinct from those of the recent or un weathered group. These have profiles with clearly evident clay accumulations in the mod- erately compact subsoil layers, while many of the soils also have accum- ulations of lime in the subsoil. Subsoils are permeable to moisture and roots, although not to the same degree as the younger soils of group I. TYPE JT^asr*-™^ ^a^JLi Z»yy*^± _ LOCATION _££ ^^S^^Y^P^t-— dQ^^tJQ^g' £**r$H_. RELIEF ^^2^^*>t«ee. ELEVATION J^J^jjffti _ DRAINAGE _ J^>j43 4 nj ^A: RAINFALL JZ. «2»?*«± NATIVE VE6ETAT10N _Q^a^>~_- J>"±f^L_ USE _WjM~J^3- 1 ORIGIN'S*"*^!*^ -| ,% ^ > rir g^^ife DEVELOPMENT OF PROFILE J=*T^ i? M 5i-'~l. ^^t^*X^_ REMARKS U^Cj^u^o _a. p.a&*^_ f) 9Q. _ STRUCTURE CONSISTENCE AND DENSITY MISCELLANEOUS ROOTS, STONES, CONCRETIONS, PCRMEABIMTY, ETC. "EL "t«^wJ,*L^ -rvu<JL f^Lh^JL^Mx. TfH JLfrOJtrKS a^Loyr^iiiaH, n.o »»*>i-»~L-e<-£C«_ 7.6 - 73 ■+, J /C0tV»*v yofVOKt ***f 7.0 Fig. 2. — Profile description of Eamona sandy loam, San Diego County, California, illustrative of the general characteristics of the soils in group II (moderately weath- ered secondary soils), having compact subsoil layers with clay accumulations. This is evidenced by the somewhat slower penetration of irrigation water. The parent material below the subsoil is usually permeable to a depth of 6 feet or more. These soils usually occur on smooth terraces and mesas, lower benches, and in some cases on typical alluvial-fan sur- faces, usually being slightly higher in elevation than those of group I. Many of the soil series in this group occur on terraces which have been slightly eroded so that the topography is somewhat irregular, especially on the borders. These are good soils, although of less value than those of group I, since they are older, have a moderate subsoil compaction and accumulation of clay, which retards the penetration of moisture, and may have a more 14 University of California — Experiment Station irregular surface, which lessens their value for irrigated crops. They are given a factor- A rating of 80-95 per cent. Soils of the Ramona series are the best known in this group. A typical profile description of Ramona sandy loam is given in figure 2. GROUP III, STRONGLY WEATHERED SECONDARY SOILS WITH DENSE CLAY SUBSOILS (SEMIMATURE SECONDARY SOILS) The soils of group III are characterized by a very heavy, dense, plastic clay subsoil layer that breaks up when dry into very hard dense struc- tural aggregates. These are semimaturely weathered soils. They are of TYPE Jhy^L t> -^--4^L ■<**2fpi &*?"?— LOCATION _ Qs*^£u^^_y^<r^«^^L _Ht"<=?yL' RELIEF. fX^L'^^P 2 -— ELEVATION _ _ _4P^^ DRAINAGE ^^J^y^±^. RAINFALL J8. hr^^L. _ NATIVE VE6ETATI0N _<3/c^O^<. _ _ USE ~Eo^aa. ORIGIN _ J^kpd 2"-*X*iV-*L DEVELOPMENT OF PROFILE _ ^y^s^&& . REMARKS _ _— _ _ — — ■ Th&UL. Ka&y±g. _jrP—<S>Cl COLOR STRUCTURE CONSISTENCE AND DENSITY MISCELLANEOUS ROOTS, STONES, CONCRETIONS, PERMEABILITY, ETC. JLbrxsm, *¥4 except ianyhj LcrtMy &v*ch OAAM^Jl jLytrZA. ^RJs Orr&.icf' eM^&J /V^> ^-f' JLo-a^r^/ JUlLj d-oSAJU* Jt Fig. 3. — Profile description of Antioeh fine sandy loam from Solano County, Cali- fornia; claypan soil of group III. alluvial or marine origin, but have been materially changed in chemical and physical make-up since they were deposited. All have a leached surface usually of sandy texture, low in available plant food, and nor- mally moderately acid in reaction. There is usually an abrupt change from the sandier surface layers to the heavy, dense clay subsoils. The downward movement of water is markedly retarded and the soils be- come temporarily water-logged after heavy rains. The heavy subsoils are underlaid by pervious parent materials penetrable by roots and water. In some cases these parent materials are loose soil, while in others they are fairly compact, but in all cases they are penetrable to a depth of 6 feet or more. Bul. 55(5 J Index for Rating Value of Soils 15 These soils occupy terraces or benches which are often somewhat eroded. They are of common occurrence in most of the California valleys and along the coast line of central and southern California. Their value is limited by the heavy subsoil layer and often to some extent by the eroded surface, which makes them difficult to irrigate and cultivate. They are given a rating of 40-80 per cent. Within these limits the rating will depend on the depth to the clay layer and the general surface conditions. Soils occurring under higher rainfall, such as the Fig. 4. — Profile of San Joaquin sandy loam (hardpan soil, group IV), San Joaquin Valley, California. The hardpan layer is about 2 feet thick, with about 3 feet of soil material overlying the hardpan. (Photograph by C. F. Shaw.) Antioch series, have surface soils as much as 20 to 24 inches in thickness, while the southern California soils of similar character (such as the Huerhuero series), but located where the rainfall is much less, have much shallower surface soils. Figure 3 gives details of a profile of the Antioch fine sandy loam located near Fairfield. This soil is given a higher rating than the Huerhuero because of its depth of surface soil and the level surface of the terrace on which it occurs. GROUP IV, MATURELY WEATHERED SECONDARY SOILS WITH HARDPAN The soils with hardpan appear to have reached a mature age or stage of weathering, and are characterized by the cemented, rock-like subsoil horizon (fig. 4) that has been formed as a direct result of the soil- weathering process. True hardpans do not soften when saturated with 16 University of California — Experiment Station water, thus being distinguished from certain dense clay subsoils, which are often erroneously referred to as hardpan layers. True hardpan soils occur under arid or semiarid climatic conditions, and the depth to the hardpan layer is usually closely correlated with the depth of the annual penetration of rainfall. A dense clay layer nor- mally lies just above the hardpan. Where the hardpan is continuous and unbroken, drainage conditions are poor and the surface soil becomes saturated after heavy rains. They usually occur on sloping terraces or on valley floors and often have a "hogwallow" surface of small mounds and depressions (fig. 5). Some areas have suffered considerable erosion. Fig. 5. — Natural mounds or "hogwallow" surface of San Joaquin sandy loam, Kern County, California. (Photograph by C. F. Shaw.) The largest areas of hardpan soils lie in the Great Valley of Califor- nia, especially in the San Joaquin. They are also scattered throughout the valleys of southern California. They occupy a total of over three million acres in the state-. Considerable discussion has developed over the subject of the utiliza- tion of hardpan soils and the extent to which the undesirable features, such as the limited depth of the soil material overlying the hardpan and the thickness and hardness of the hardpan, may reduce the value of such soils. The rooting zone of plants is limited when the hardpan is close to the surface. The moisture capacity is limited by the shallow depth of soil above the hardpan; irrigation water must be applied frequently and in small amounts, or saturation and poor drainage will result ; and other difficulties arise owing to the limited mass of soil material. The organic content of hardpan soils is usually low, and the clay fractions of such character that the soils have a tendency to bake hard on drying, thus rendering them more difficult to handle. The undulating hogwal- low surface configuration of such lands also renders them difficult to Bul. 556] Index for Rating Value of Soils 17 prepare for irrigation. When they are leveled, it is noted that crops re- spond better in the filled places than they do on the areas where soil has been removed. The following ratings are based on the depth to hardpan : Rating, in per cent Hardpan less than 1 foot 5-10 1 to 2 feet 10-20 2 to 3 feet 20-30 3 to 4 feet 30-40 4 to 6 feet 40-60 These figures should be raised in certain instances where the hardpan is soft or broken or occurs in thin plates. A typical profile of San Joaquin sandy loam, a red "iron" hardpan soil, is given in figure 6. TYPE ^J^^^A^^<^lnJ^y^r^. LOCATION 7Wj^4*J^-i'^t*4A \/o£JIsm. _ nCUEr $k%fo&££Zt: ELEVATION 25P_|ifC _ DRAINAGE S^4j^^%*ctn£<&£ RAINFALL _//_^2^~^L _ NATIVE VE6ETATION JSvla^u _ _ _ USE _ T^Gi/UL — ORIGIN ^^r^4^±-4^I^^AS^JL DEVELOPMENT OF PROFILE ~yt\^^S^_ -^tuithtyuL _ _ — REMARKS _ "7t^_V\*>^-£^4jP4^-£*tJI _ — — _ — — — /ia/u*^, trL ZS". COLOR ?^f4 STRUCTURE GONS'STEKCE AND DENSITY MISCELLANEOUS ROOTS, STONES, COUCHETIONS, PERMSABIi-VTt, ETC. ">nff-o4_ , T\4s%JL AcU I VI. AjV^. pJL'\S^L ~#4 UOJL, jggk "MSjuXHaJ lic^ur^n^Ke- J^ 4l~k. 3E3? <JLnA«_ / at'v*ot*"«-»4. frasa<c -]QW>~*- M Fig. 6. — Profile description of San Joaquin sandy loam, a typical hardpan soil of group IV. GROUP V, STRONGLY WEATHERED SOILS WITH DENSE CLAY SUBSOILS RESTING ON CONSOLIDATED MATERIALS Soils of group V are common along the coastal plain of California. Their value is relatively low because of the leached surface, the heavy- textured subsoil, and particularly because of the hardpan-like substra- tum which, although composed of sediments, is essentially rock-like in its nature (fig. 7). Surface soils are normally somewhat acid in reaction. There is usually an abrupt change from the surface layer to the heavy dense clay subsoil, and after heavy rains these soils become temporarily water-logged. 18 University of California — Experiment Station With two exceptions, the Stockton and Landlow, all the soil series so far mapped occur on high terraces which have been subjected to con- siderable erosion. The Stockton and Landlow soils occur on flat, poorly drained plains, and instead of being sandy have heavy-textured surface soils. In this group the surface soils overlying the clay subsoils are usually less than 15 inches in thickness, and the clay subsoil varies from 10 to 24 inches in thickness. Thus the consolidated substratum is found at from 15 to 48 inches below the surface. Fig. 7. — Profile of Olivenhain loamy fine sand from San Diego County, California. Note the sandy surface soil lacking structure, the heavy-textured, dense subsoil, which breaks up into columnar structure when dry, and the massive consolidated sub- stratum. This is a typical soil of group V. (From Bui. 552.) In rating the soils of this group for factor A the points considered are the depth to the clay layer, the depth to the substratum, the nature of the substratum, and the surface relief. The range in rating is from 20 to 40 per cent. Surface texture and other factors are handled under fac- tors B and C. Soils of the Olivenhain, Tierra, and Las Flores series, which are typ- ical of this group, have similar sequence of horizons, and differ mainly in color. A profile of Olivenhain loamy fine sand from the coastal plain of San Diego County is given in figure 8. The factor-A rating of this soil is 25 per cent. Bul. 556] Index for Rating Value of Soils 19 TYPE J^-^c^La^ji^^y-i £^Ajx»<fL LOCATION _ _~_*£y _^_^ _"*_-_ _ e 'fc. _ t/> _.-£_*J_' RELIEF _^^-_ J __ : ? , _ ct ELEVATION _ _f_P-__ — DRAINAGE _^^^ a _ Y _$_- _*°_ : _ J _"_' RAINFALL _ i>_ IJ>1 _ _ NATIVE VEGETATION _Sho?£ ^*4 USE _ «_yt^r_: *f»*_ a, fp 4 '- ORIGIN /^cx*^J&W«L. _ C £ V ELOPMENT OF PROFILE _^_>~_>*_^_' t _ _____ REMARKS _ — _ _ — _ — _ — - Jh$M K-aMA\*t _jr. LZSL __ _ . PROFILE COLOR TEXTURE STRUCTURE CONSISTENCE AND DENSITY REACTION MISCELLANEOUS ROOTS, STONES, CONCRETIONS, PERMEABILITY, ETC. XUvL i&bmL iWo_- P HG.Z n •<fc~" /vOtrCo> 0T T m ~3%tvcn*mj 12- " 'H Ordbuici 7 ? 24- 3f- E tnacAtAK. 48- — - 60- Fig. 8. — Profile description of Olivenhain loamy fine sand, typical of coastal plain soils having dense clay subsoils (group V). GROUP VI, SOILS DEVELOPED ON BEDROCK (PRIMARY OR RESIDUAL SOILS) Soils of group VI have been formed by the disintegration and decom- position of the underlying parent bedrock (fig. 9). Shaw 6 has termed them primary soils. They are also referred to in soil literature as resid- ual soils. They are the hill lands of California, occupying a topography that is rolling, hilly, or mountainous (fig. 13) . Their characteristics are determined to a large extent by the character of the parent bedrock and the rainfall of the region in which they occur. Often they are shallow and stony. These factors, together with the topog- raphy and surface configuration, determine their value. Because of their slope, they are more difficult to farm than the terrace and valley lands. The steep slopes have a tendency to erode badly, especially when culti- vated. The normal progress of erosion is the main factor that keeps most primary soils from reaching a mature stage of soil weathering. Most of the primary soils have a moderate accumulation of clay in the subsoils as a result of soil weathering, but not nearly so much as exists in soils of groups III, IV, or V. Usually the upper portion of the underlying parent bedrock has been softened by weathering action so that roots and mois- ture have an opportunity to work their way down into the bedrock through cracks and crevices for some distance. 6 Shaw, C. F. A definition of terms used in soil literature. Sci.Proc. 5:38-64. 1928. Intntl. Congr. Soil 20 University of California — Experiment Station . ;, . Fig. 9. — Profiles of shallow primary soil (group VI), Sierra Nevada foothill district. TYPE B*M*~4? ^^±. ^»2^y_ _ LOCATION SltstA^. Tl^oyJa. jW^."^lA«>S?l RELIEF. J^^h ELEVATION -T^L-Af^ _ DRAINAGE _ l^WL^^Li^JL RAINFALL 30_^>ycXsS- NATIVE VE6ETATION i?/Wj£t. QaA, _ USE J = ^r^o^^xxeLxi, __ ORIGIN _T2^o^_A«^J^^ 4*142^ J3EVELOPMENT OF PROFILE REMARKS _ ~F ktriU U Hafcyz 61 t>S STRUCTURE r (Mvdtan, CONSISTENCE AND DENSITY Fig. 10. — Profile description of Holland sandy loam in the Sierra Nevada foothills. This is a primary or residual soil of group VI. AU.JL * -yicJbJttJL MISCELLANEOUS ROOTS, STONES. CONCRETIONS, PERMEABILITY, ETC. TZVVmuC&J? -try fr&vt&. ~rzjLn*~*-*XLJl '9*1 K^&Zg. S<r«v» ^oVU^JUi' f<2ry Bul. 556] Index for Rating Value of Soils 21 Considerable variation is encountered in depth and stone content, and such variations are considered in rating these soils. Typically, primary soils are well drained and contain no alkali so that these factors do not have to be considered under factor C. Texture of the surface soil is largely governed by the type of parent bedrock. Coarsely crystalline rocks, such as granites, usually give rise to sandy soils, while the finer-textured rocks, such as the andesites, weather into clay loam types. Some of the better-known primary soils are those of the Holland, Sierra, and Aiken series of the Sierra-Nevada foothills. The Aiken is the very red primary soil derived mainly from andesitic parent bedrock, while the other two are brown and red granitic soils. A profile descrip- tion of a Holland sandy loam of the Sierra-Nevada foothill district is given in figure 10. The ratings given the primary soils are based on the depth of soil ma- terial overlying bedrock, as follows : Rating, in per cent Less than 1 foot- 20-25 1 to 2 feet 25-40 2 to 3 feet 40-60 over 3 feet 60-70 FACTOR B : TEXTURE OF SURFACE SOIL Factor B rates the soil on the basis of the characteristics of the sur- face soils, independent of the subsoils. It is a rating of the soil textures and those other characteristics that are more or less dependent on tex- ture, such as the consistence (hardness or softness) of the soil aggre- gates, the porosity of the soil mass, the permeability to water, the tilth (response to tillage operations), and similar characteristics or reactions. These are so dominated by texture that a rating on the textural basis will also express the general effect of these features. Textural grades, designated in popular terms such as sandy loam, loam, and clay loam, express the mass effect of the amounts of different- sized grains that constitute the soil. The physical composition of a soil can be accurately determined by a mechanical analysis which separates the soil into grain-sized groups. The limits of the amounts of the grain- sized groups present in any textural grade have been definitely estab- lished. 22 University of California — Experiment Station TABLE 3 Textural Grades of Soils' Grade Coarse sand.. Sand. Fine sand Very fine sand Sandy loam. Fine sandy loam Very fine sandy loam Loam.. Definition* Contains less than 20 per cent silt and clay, and more than 35 per cent fine gravel and coarse sand grain sizes, and less than 50 per cent any other grade. Contains less than 20 per cent silt and clay, and more than 35 per cent fine gravel and coarse sand and medium sand, and less than 50 per cent fine sand. Contains less than 20 per cent silt and clay, and more than 50 per cent fine sand, and less than 25 per cent fine gravel and coarse and medium sand. Contains less than 20 per cent silt and clay, and more than 50 per cent very fine sand, and less than 25 per cent fine gravel and coarse and medium sand. Contains between 20 and 50 per cent silt and clay, and more than 25 per cent fine gravel and coarse and medium sand, and less than 35 per cent fine or very fine sand. Contains between 20 and 50 per cent silt and clay, and more than 50 per cent fine sand, and less than 25 per cent fine gravel and coarse and medium sand. Contains between 20 and 50 per cent silt and clay, and more than 35 per cent very fine sand, and less than 25 per cent fine gravel and coarse and medium sand. Contains more than 50 per cent total silt and clay, and less than 20 per cent clay, from 30 to 50 per cent silt, and from 30 to 50 per cent sands. Obvious characteristics Sands are loose and granular. The indi- vidual grains can readily be seen and felt. Squeezed in the hand when dry the ma- terial will fall apart when the pressure is released. Squeezed when moist, it will form a cast but will crumble when touched, although fine sand and very fine sand have a certain amount of cohesion when moist. Contains much sand but which has enough silt and clay for coherence, gritty feel; sand grains can be seen. Squeezed when dry will form a cast which will readily fall apart, but if squeezed when moist a cast can be formed that will bear careful handling without breaking. Classed as coarse, medium, fine or very fine sandy loam, depending on the proportion of the different-sized particles that are present. Even mixture of different grades of sand, and of silt and of clay. Mellow, of some- what gritty feel, yet fairly smooth and rather plastic. Squeezed when dry it will form a cast that will bear careful han- dling, while the cast formed by squeezing the moist soil can be handled rather freely without breaking. * For ratings see table 4, page 38. t The grades are defined on the basis of the amount of the several grain-sized groups of particles found in them upon mechanical analysis. For the sizes of the soil-particle groups see footnote 7, page 24. Bul. 556] Index for Rating Value of Soils 23 TABLE 3— (Concluded) Grade Silt loam.. Clay loam. Silty clay loam Clay. Silty clay. Adobe clay or clay adobe Definition Contains more than 50 per cent total silt and clay, and less than 20 per cent clay, more than 50 per cent silt, and less than 50 per cent sands. Contains more than 50 per cent total silt and clay, and 20 to 30 per cent clay, and less than 50 per cent silt or sand. Contains more than 50 per cent total silt and clay, and 20 to 30 per cent clay, more than 50 per cent silt, and less than 30 per cent sand. Contains more than 30 per cent clay, and less than 50 per cent silt or sands. Contains more than 30 per cent clay, more than 50 per cent silt, and less than 20 per cent sands. Contains more than 30 per cent clay, particularly the ultra or col- loidal-clay particles, and less than 50 per cent silt or sands. Obvious characteristics Moderate amount of the fine grades of sand and only a small amount of clay, over half of the particles being of the size called "silt." When dry it may appear cloddy but the lumps can readily be broken, and when pulverized it feels soft and floury. Either wet or dry the soil will form a cast that can be freely handled without break- ing. If squeezed between the thumb and finger it will not "ribbon," but will give a broken appearance. A clay loam in the field is dense and com- pact, and breaks into clods or lumps, which when dry are hard to break. When the moist soil is pinched between the thumb and finger it will form a thin "rib- bon" that will break readily, barely sus- taining its own weight. Moist soil is plastic and will form a cast that will bear much handling. When kneaded in the hand it does not crumble readily but tends to work into a heavy compact mass. Silty clay loam contains more of the par- ticles termed "silt" so that the soil is less plastic than the clay loam. Dense and compact, forming very hard lumps or clods when dry. Composed of very fine particles which when wet stick together to make a very putty-like and plastic mass. When the moist soil is pinched out between the thumb and fingers it will form a long flexible "ribbon." Silty clay contains more of the particles termed "silt" so that the soils break down more readily than a clay. In addition to characteristics of clay, adobe clays contract on drying, producing large cracks and blocks. Secondary cracking may cause them to break into smaller fragments. The term "adobe" alone, refers to this structure produced by shrinkage on drying. 24 University of California — Experiment Station The various textural grades of soils are listed in table 3, with the amounts of the grain-sized groups (determined by mechanical anal- ysis), 7 and some of the obvious physical characteristics of the various soil textures. The major textural grades give very characteristic re- sponses when rubbed between the thumb and fingers, and when kneaded and molded while wet. With practice, the textural grade of a soil can be approximated by this hand test, which aids in determining the texture when soil maps are not available. Texture or physical composition controls, to a large degree, the water- holding capacity, permeability to moisture, ease of tillage, plasticity, the stickiness of the soil when wet, and the friability and hardness when dry. Soils having ideal conditions from the textural standpoint as reflected in these physical characteristics are rated at 100 per cent in factor tB. Soils having less favorable textures are rated according to their relative order. Soils with a large percentage of sand or gravel are relatively low in the plant nutrients and do not retain moisture so well as do those of finer texture. At the other extreme heavy-textured soils, those having a high percentage of clay particles, are more difficult to handle and have other disadvantages, although they may contain a maximum of moisture and plant nutrients. It must be borne in mind that the ratings on soil texture are on a rela- tive basis and can be varied to some degree as conditions may warrant. MEDIUM-TEXTURED SOILS Rating, in per cent Fine sandy loam 100 Loam 100 Silt loam 100 Sandy loam 95 Coarse sandy loam 90 Loamy sand 80 The medium-textured soils are given the highest rating since they do not contain an excess of either the sand or the clay, have a medium-soft consistence, take water readily yet have a good water-holding capacity, are friable and easy to cultivate, do not readily puddle or form clods, and in general are most easily maintained in a condition of good tilth. 7 Eight grain-sized groups have been adopted by the United States Department of Agriculture with the effective diameter of the particles as indicated below: Diameter in millimeters Name of size group 2.0 - 1.0 fine gravel 1.0 — 0.5 coarse sand 0.5 - 0.25 sand 0.25 - 0.10 fine sand 0.10 - 0.05 very fine sand 0.05 - 0.005 silt 0.005 - 0.002 coarse clay 1 less than 0.002 ultra or colloidal }• clay clay J Bul. 556] Index for Rating Value of Soils 25 Fine sandy loam, 8 loam, and silt loam are given the highest textural rat- ing. They have a fairly high water-holding capacity (18 to 40 per cent by dry weight), and a high amount of available water. These are the best-textured soils for such intensive crops as vegetables, which have to secure their moisture and plant nutrients from a relatively small volume of soil. Sandy loams are rated slightly lower since they do not have the power to hold as much moisture, and so do not have quite the range in use that the fine sandy loams, loams, or silt loams have. Coarse sandy loams have a still lower water-holding capacity and usually less organic matter and plant nutrients, and so are rated lower than the sandy loams. Loamy sands hold 5 to 9 per cent of moisture as against 10 to 13 per cent by sandy loams. For most crops they do not have as much potential value as the slightly heavier-textured soils even though they are easy to handle at any moisture content. They have a fairly high value for cer- tain specialized crops that are grown along the coast, such as winter squash, peas, etc. MEDIUM-HEAVY-TEXTURED SOILS Rating, in per cent Silty clay loam 90 Clay loam 85 Silty clay loam and clay loam soils have a high water-holding capacity (25 to 40 per cent), but puddle rather easily and have a tendency to be- come hard on drying. Their general range in cropping adaptation is lower than the loam or silt loam since they take water more slowly, are harder when dry, and more power is required in the use of tillage imple- ments. Silty clay loam is somewhat easier to till than the clay loam be- cause of the higher silt content. Certain calcareous types of both the silty clay loam and clay loam are more friable owing to the high lime content. As a general rule, soils of these textures are fertile and highly productive in California. HEAVY-TEXTURED SOILS Rating, in per cent Silty clay 60 Clays and adobe clays 50-70 8 In classifying the yields of oranges on different soil types in southern Cali- fornia, Vaile states that "the groves planted on medium-textured soil (fine sandy loam) gave the highest average yield." (Vaile, Roland S. Survey of orchard prac- tices in the citrus industry of southern California. California Agr. Exp. Sta. Bul. 374:11, table 6. 1924.) It is significant that only about 5 per cent of the groves were planted on very light soil (sand) and that these groves produced 30 per cent less than those on medium-textured soil, while only from 5 to 10 per cent of the groves were planted on medium-heavy soil and these produced 10 per cent less than those on the medium-textured soil. 26 University of California — Experiment Station The properties of silty clay and clay soils are largely governed by the character of the clay particles that make up from 30 to 60 per cent of the soil mass. Often a large proportion of the clay particles are of the ultra- clay or colloidal-clay size and exhibit the physical properties of colloids. Clay soils are cold and sticky when wet, and very hard when dry. The high clay or colloidal content impedes the movement of water, causing water-logged conditions in wet weather and lack of available moisture during the dry season. When dry, they shrink and crack, frequently breaking into large, hard blocks with wide cracks between, giving the structure known as "adobe clays." As a result they are not so desirable as the lighter-textured soils. They are best adapted to crops, such as grain and rice, for which heavy machinery is needed. Most clays are improved by the addition of lime or other flocculating materials, which cause the soil to form aggregates with definite struc- tural properties, and results in a decrease in the plasticity and hardness of the mass. This materially increases the ease of tillage. On the other hand, certain of the alkali salts exert a deflocculating effect on the soil mass, making it less pervious and more difficult to till. Organic matter acts very much in the same way as lime on clay soils, but the amount has to be high and frequently applied in order to make much improvement in the physical condition. Clays generally are high in plant nutrients, but physical factors such as plasticity, penetrability, and drainage overshadow these desirable chemical characteristics. Silty clay is a little more friable owing to the higher content of silt. LIGHT-TEXTURED SOILS Rating, in per cent Very fine sand 80 Fine sand 65 Sand 60 Wind-blown sands 20-70 The sands listed above differ in the relative size of the sand particles making up the soil. All have less than 20 per cent total silt and clay par- ticles. The large proportion of sand particles renders these soils open and friable. Water percolation through the soil mass is fairly rapid and is liable to be excessive in the coarser sands. Air moves rapidly through sandy soils and they warm up more quickly in the spring than do heavier- textured soils. This factor renders them desirable for certain specialized truck crops. The wide range in the rating of wind-blown sands — 20 to 70 — is due to the great variation in the surface configuration of this type of material. Soils of the Rositas, Coachella, and Oakley series are typical examples Bul. 556] Index for Rating Value of Soils 27 of wind-blown material. The shifting of sand by wind action causes serious difficulties in certain instances. The cost of leveling this type of material for irrigation is relatively high. The available plant nutrients of sands are low. Large applications of organic material in the form of manures or covercrops are necessary to maintain yields on them, and frequent application of fertilizers is neces- sary in order to maintain their valne for intensive cropping. Moisture must be available at regular intervals during the growing season. This interval and application is necessarily relatively short since the mois- ture-holding capacity of the sands is small compared with that of the medium-textured soils. The normal moisture capacity will vary from 2-3 per cent in the coarse sand up to 7-10 per cent for the very fine sand. Thus it can readily be seen that the value decreases with the coarseness of the soil. Sands occurring where there is a high rainfall are leached of their plant nutrients and are usually of very low productive value. For- tunately, the area of such soils in California is limited largely to the northern coast line. Some of the southern coastal plain sands have been moderately leached, but the arid and semiarid sands are fairly good pro- ducers when moisture and sufficient organic material are present. GRAVELLY OR COBBLY SOILS Rating, in per cent Gravelly fine sandy loam 70 Gravelly loam 70 Gravelly silt loam 70 Gravelly sandy loam 65 Gravelly clay loam 55 Gravelly clay 35 Gravelly sand 20-30 The presence of gravel in a soil interferes with tillage operations, and, especially in the case of the lighter-textured soils, materially lowers their water-holding power. Suggested ratings are given above. These may have to be lowered or raised according to the amount of gravel present in the soil mass. STONY SOILS Rating, in per cent Stony fine sandy loam 70 Stony loam 70 Stony silt loam 70 Stony sandy loam 65 Stony clay loam 60 Stony clay 35 Stony sand 10-40 Stone in a soil interferes with tillage and all farm operations, and lowers the water-holding capacity and the volume of actual soil from which plants can secure food. The rating of soils containing enough 28 University of California — Experiment Station stone to interfere with farm operations should be lowered. Suggested ratings are given above where the soils have been mapped under such type names in the soil surveys. FACTOR C : SOIL-MODIFYING CONDITIONS As mentioned previously, a number of other conditions may exist that modify the value of the soil. These are generally determined by field observations or by a few simple field tests. They are listed with suggested ratings under the following headings and in table 4 (page 38) . DRAINAGE Soils having a high water table or a fluctuating ground-water level are obviously of lower value than those which are well drained. The past drainage history and the prospects of the soil's becoming water- logged under future utilization should have careful consideration in any system of soil evaluation. Many of the dark-colored alluvial soils are poorly drained, especially those at the lower ends of the alluvial fans where water has accumulated by seepage from the higher lands. Drain- age conditions are divided into four classes, each given a rating. 1. Well Drained .... 100 per cent. — Soils are considered well drained where the water level is deep and there is no probability of the soil's be- coming water-logged. 2. Fair Drainage .... 80-90 per cent. — Drainage is considered fair where the water table is sufficiently below the surface so that little crop injury is experienced, and where any excessive water can be taken care of through artificial drains at a low or moderate cost. Areas where there may be some shallow flooding for brief periods are also placed in this class. 3. Moderately Water-logged .... 40-60 per cent. — Soils are consid- ered moderately water-logged where the permanent water table is suf- ficiently close to the surface so that only the shallow-rooted crops can be grown. 4. Badly Water-logged .... 10-40 per cent. — Land is considered badly water-logged where the ground water is permanently close to the sur- face, so that agriculture is limited to very poor wild grasses. ALKALI Alkali is often the limiting factor governing the value of desert soils. It consists of an excess of soluble salts that have accumulated in the soil because of poor drainage and excessive surface evaporation (fig. 11). Bul. 556] Index for Rating Value of Soils 29 Chemically, they may be sodium chloride, sodium sulfate, sodium car- bonate, etc. Alkali is not normal to humid soils of the eastern part of the United States since it cannot accumulate where there is a high rainfall and the soils are leached. Recognizing the importance of alkali, careful studies are made of this problem in the soil surveys of desert areas. The harmfulness of alkali is dependent not only on the amount present in the soil, but on its position in the profile, its chemical composition, the texture of the soil, and the Fig. 11. — White alkali crust, with a native cover of grease wood. This soil is of no value for agriculture because of the high alkali content. (Photograph by W. W. Weir.) amount of moisture present. Plants do not tolerate a great deal of alkali if it is concentrated as a surface crust, or if it is of the "black" variety (sodium carbonate) , or if it is concentrated in a dry soil. In mapping the alkali of an area such lands have often been classed in four grades 9 with reference to the total content, the kind of alkali, and the visible conditions such as the appearance of the crop or the pres- ence of alkali-tolerant weeds growing on the land (fig. 11). 1. Alkali-free: 100 per cent. — This grade includes areas whose salt content is less than 0.2 per cent and so evenly distributed throughout the soil profile as to be noninjurious to crops. 2. Slightly Affected Areas: 90 per cent. — This grade includes areas whose salt content is usually between 0.2 and 0.6 per cent, but so dis- tributed throughout the soil profile as to have only slight effect on crops. 9 Strahorn, A. T., et al. Soil survey of the El Centro area, California. U. S. Dept. Agr. Bur. Soils, pp. 641-716. 1918. 30 University of California — Experiment Station 3. Moderately Affected Areas: 60 per cent. — This grade includes land with a salt content of less than 2 per cent, which is so distributed in the soil profile as to depress the yields of crops, but not prevent their growth. Soils with a much smaller amount of black alkali are rather toxic. 4. Strongly Affected Areas: 5-25 per cent. — Crops are limited and to a large degree prohibited by the alkali content in these areas. The total amount of salts may vary from 1 to 2 per cent or more, as an average throughout the profile, but is usually high in the surface foot — often over 3 per cent. Some of these areas have practically no value for agri- culture. Soils with much smaller amount of black alkali (sodium car- bonate) may be rather toxic and should be placed in this grade. ACIDITY A number of soils exist in California which are acid in reaction (table 1, page 7). The rating of acid soils is reduced according to the degree of acidity, for most crops are injured by excessive acidity of the soil. Suggested ratings vary between 60 and 95 per cent. The hydrogen-ion concentration (usually expressed as pH) of soils is a measure of the in- tensity of acidity. Soils with a pH of about 7.0 are said to be neutral in reaction ; those with a pH of 6.0-6.5, slightly acid ; those with a pH of 4.5-6.0, moderately acid; and those with a pH below 4.5, very acid. Alkaline soils have a pH of over 7.0. Soil acidity can be quickly and easily determined by simple tests. A number of field testing kits, satis- factory for approximate determinations of soil reaction, are available. INFERTILITY Information can usually be secured about the general fertility of a soil by studying the past cropping history. Where a soil is of lowered fertility, its rating can be lowered by applying a factor here to take care of this. In most cases this will be between 80 and 95 per cent, although in some extreme cases a lower number should be given. A routine chemical analysis does not give very much information re- garding the adaptability of soils to crops, or methods of fertilization, 10 so that field observations on the cropping history and the native vegeta- tion growing on the soil must be used to supplement other information regarding the availability of plant nutrients. Often valuable informa- tion can be secured by studying the distribution of crops on each soil series or soil type. Where agriculture has been long established in a re- !o Hoagland, D. R. Fertilizer problems and analysis of soils in California. Cali- fornia Agr. Exp. Sta. Cir. 317:1-16. 1930. Bul. 556] Index for Rating Value of Soils 31 gion this information is of great value in rating the productive capacity of the respective soils. "Worn out" or infertile soils can be determined by such a study. STRATIFIED SUBSOILS (GRAVELLY LAYERS OR STRATIFIED CLAY LAYERS) Where moisture is a limiting factor in crop growth, the presence of gravelly layers in the alluvial soils is a distinct handicap, since such subsoils are of leachy character with little power of holding moisture for crop use. These gravelly pockets, or subsoil layers, are most common in soils of the Tujunga, Hanford, Yolo, and Elder series, which are of fairly recent deposition. Such pockets are a result of the deposition of gravelly material by fast-moving water, and later deposition of finer and better surface soil over it. These "pockets" are not obvious from surface soil examination, except that crops may appear wilted where there is a deficiency of moisture. The rating given soils having such conditions will naturally vary, although a rating of 80-95 per cent will take care of most cases. Certain alluvial soils having heavy-textured layers in the subsoils should be discounted' in value to some extent. Fairly large areas of soils having such conditions exist in the Imperial Valley. A rating of 80-95 per cent is suggested to cover such conditions. SHALLOW PHASES OF ALLUVIAL SOILS In certain extreme cases alluvial soils may be only 2 or 3 feet deep over a flat substratum or bedrock. A rating of 50-60 per cent might be given for a 2-foot depth of soil, and a rating of approximately 70 per cent for alluvial soils about 3 feet in depth. ERODED SOILS All soils located on slopes erode or wash to some extent. Under certain conditions of rainfall and removal of the vegetative cover by cultiva- tion, overgrazing, lumbering, and fire, this is hastened, and the soils erode to such an extent that their value is materially lowered 11 (fig. 12) . Soils eroded to a moderate extent might be given a rating of 80-95 per cent, while the badly eroded soils, such as those mapped as eroded phases, should be given a much lower figure. ii Weir, Walter W. Soil erosion in California: its prevention and control. Cali fornia Agr. Exp. Sta. Bul. 538:45. 1932. 32 University of California — Experiment Station STEEP PHASES Soils occurring on steep slopes are difficult to till, and should be low- ered in their rating. Rough mountainous slopes are of still less value. A range in the rating may be 60-80 per cent for soils occurring on slopes that are fairly difficult to till, and 20-30 per cent for soils on steep moun- tainous slopes. ,-i Fig. 12. — Eecent erosion cuts 2 to 3 feet in depth have materially lowered the value of this field. Note deposition of eroded soil material on the flat. (From Bui. 538.) NONAGRICULTURAL MATERIALS In most of the soil surveys there is a miscellaneous class of materials that is not classed with the soil series or soil types, but classed under a miscellaneous group. This has little value from an agricultural stand- point. For purposes of rating them, these are given an index, although they really belong in a system of land classification rather than in a soil category. Nonagricultural materials which are mapped under miscellaneous group in soil surveys are as follows : 1. Rough Mountainous Land: 5-10 per cent. — This class of land usually occurs on rougher mountainous topography; it is often good grazing land (fig. 13). 2. Scabland: 5 per cent. — Scabland consists of fairly recent lava flows ; contains small patches of soil (fig. 14) ; it is of very little agricul- tural value even for grazing. Bul. 556] Index for Rating Value of Soils 33 Rough Broken Land: 5 per cent. — Rough broken land consists of steep slopes, eroded slopes, gullies, and canyon walls, and contains very small areas of arable land. 3. Riverwash : 1-5 per cent. — Riverwash consists of sandy, gravelly, cobbly, or stony deposits of stream channels; subject to erosion and overflow ; of no agricultural value. Fig. 13. — Eough mountainous and rough stony land. Note small cleared area of primary soil (group VI soils). (From Bul. 552.) Fig. 14. — Scabland: a very thin layer of soil weathered from fairly recent lava flow. It is of very low value. (Photograph from C. F. Shaw.) Placer Diggings and Tailings: 1-5 per cent. — Areas where placer- mining operations have left the surface covered with stone and gravel are placed in this class. Tidal Marsh: 1-5 per cent. — Tidal marsh lands are lands subject to inundation by tidal action ; they are low, flat, and highly saline. 34 University of California — Experiment Station Coastal Beach: 1-5 per cent. — This class applies to sloping beaches of sand, gravel, or stone. Dunesand: 1-5 per cent. — Dnnesand consists of areas of sand on dunes or ridges ; in more or less constant movement with wind. Rough Stony Land: 1-5 per cent. — This class includes rough, stony slopes (fig. 15). The presence of excessive amounts of stone and large rocks or boulders is the dominant factor. CALCULATION OF THE INDEX To use this index method for rating soils it is obviously necessary to know the characteristics of the soils to be rated. This information may be obtained directly by adequately exploring the soil and subsoil to a depth of 6 or more feet throughout the whole area to be rated, supple- menting this exploration by field and laboratory studies to determine the less obvious characteristics of the soil. This would require much time and patient investigation, as well as a considerable degree of training in soil studies. Most of the needed information can be obtained from the soil maps and reports if the area to be rated has been covered by the soil survey. The information available in these surveys has already been discussed to some extent, and the Appendix gives further information and lists the areas on which surveys have been completed and are available. As the soil maps are usually published on the scale of 1 inch to the mile, it is difficult to show on the maps soil bodies that are less than 5 acres in area. Hence in rating any area it is essential that the informa- tion supplied by the soil surveys be supplemented by direct field exami- nation to ascertain the less extensive and more intimate characteristics of the soils, and particularly the conditions included in factor C. From experience in the use of the index it is suggested that the se- quence given herewith be followed. 1. Ascertain the characteristics of the soil profile and especially those of the subsoil and substratum, from soil-survey data and field studies. Determine the group in which the soil belongs and develop the rating for factor A. 2. Ascertain the textural characteristics of the surface soils, checking by careful field observations to determine the direction of any local variation from the typical texture. From these studies develop the rat- ing for factor B. 3. Ascertain the presence or absence of alkali, poor drainage, or other soil-modifying conditions. These are more variable in occurrence and extent than the characteristics that determine factors A and B, and re- Bul. 556] Index for Rating Value of Soils 35 quire much more field investigation to determine the intensity of local conditions. From the results of this study, develop the rating for factor C. Unless some specific unfavorable factor is present, the rating for factor C should be 100 per cent. k% A Fig. 15. — Rough stony land, nonagricultural class. It supports growth of brush and a few trees. (Photograph by C. F. Shaw.) The final soil index is then obtained by multiplying A times B times C. The values and limits assigned to the several divisions of each of the three factors are summarized in table 4 (page 38). SOIL RATING FOR A TRACT OF LAND When a tract of land is to be rated, the soil survey, if available, is con- sulted, and a field examination is made. On the basis of these, a soil map such as that shown in figure 16 is prepared. The index for each soil type in the tract is calculated separately, and then a rating for the entire 36 University of California — Experiment Station tract is calculated by weighting each soil index according to the propor- tion of the acreage of that soil in the tract. Various tracts of land can be compared by the use of these figures. For the tract shown in figure 16, the steps in calculation would be as follows : 1. Index for Hfsl, Hanford fine sandy loam : This soil is granitic fine sandy loam of alluvial origin with no compaction or clay accumulation in the subsoil, more than 6 feet in depth, well drained, and has no alkali. It is of high productive value. Ratin in per cent Factor A: Hanford Series, group 1 100 Factor B: tine sandy loam (medium-textured soil) 100 Factor C: has no other modifying soil factors 100 ABC Index rating = 100% X 100% X 100% = 100% 2. Index for CSiCl, Chino silty clay loam : This is dark gray alluvial soil of granitic origin, with gray to dark gray subsoils which are cal- careous. The soil is more than 6 feet in depth, but has a water table at a depth of 3 feet from the surface. Rating in per cent Factor A: Chino Series, group 1 100 Factor B: silty clay loam (medium heavy) 90 Factor C: moderately water-logged 60 ABC Index rating = 100% X 90% X 60% = 54% 3. Index for Hstl, Holland stony loam : This is brown primary soil from granitic parent material. Bedrock is at an average depth of 3 feet. A considerable number of stones occur throughout soil mass. The surface is gullied to some extent. Rating, in per cent Factor A: Holland Series, group VI (depth 3 feet) 60 Factor B: stony loam (stony) 70 Factor C: eroded surface 80 ABC Index rating = 60% X 70% X 80% =33% 4. Index for R, rough stony land : The area consists of extremely stony slopes, and is of little value. Index rating = 2% Bul. 556] Index for Rating Value of Soils 37 5. The index for the entire tract shown in figure 16 may then be cal- culated according to the acreage of each soil, as follows : Soil Index Acreage Hanford fine sandy loam 100 X 95 = 9,500 Chino silty clay loam 54 X 10 = 540 Holland stony loam 33 X 65 = 2,145 Rough stony land 2 X 30 = 60 Total 200 12,245 12,245 Tract rating c= = 61. 200 SOIL MAP Or SMITH TRACT SCALE IN FEET =5= ••.. 7? HstL ft Htsl ■ ■ Hi ii ii II II / "•**•., \ II II II II / HslL CSiCL "•-.. II Ii II LEGEND ■ Main roads —== Secondary roads ■■ Buildings '•""■ Soi/ boundary Soils nfsl nan ford -fins, sandy loam CSiCL Chi no si liy clay loan) Hsi'L Hoi land stony loam /? Hough stony land Fig. 16. — Soil map of a tract of land, which is made by field examination. The figures listed below give the types, their acreage, index, and grading. Types Acreage Index Grade Hanford fine sandy loam 95 100 1 — Excellent Chino silty clay loam 10 54 3 — Fair Holland stony loam 65 33 4 — Poor Rough stony land 30 2 5 — -Very poor, non- agricultural 38 University of California — Experiment Station TABLE 4 Soil Eating Chart— For Eating or Judging the Agricultural Value of Soils (Soil Index Eating = Factor A x Factor B x Factor C) Factor A, Rating of soils on basis of character of profile Factor B, Rating of soils on basis of surface texture Factor C, Rating of conditions and char- acteristics of the soil which modify its suitability for utili- zation in plant production Soil group Rating, in per cent Texture Rating, in per cent Condition Rating, in per cent I. Unweathered or slightly weathered secondary 95-100 Medi ikm-text ured : 100 100 100 95 90 80 Drainage: 100 80-90 moderately water- II. Moderately weathered secondary soils 80-95 40-60 coarse sandy loam badly water-logged .... III. Strongly weathered 40-80 10-40 Alkali: secondary soils with dense clay subsoils, developed on uncon- solidated parent ma- Medium-heavy textured: 90 85 100 slightly affected moderately affected . strongly affected 90 60 terial Heavy-textured: 65 50-70 5-25 IV. Maturely weathered secondary soils with 5-10 10-20 20-30 30-40 40-60 Acidity: according to degree- clay and adobe clay 60-95 hardpan : Hardpan less than 1 foot Light-textured: 80 65 60 20-70 Infertility: according to degree.. 60-95 1-2 feet Stratified subsoils 60-95 2-3 feet .. Shallow phases of allu- vial soils: 3-4 feet 4-6 feet Gravelly or cobbly: gravelly fine sandy 70 70 70 65 55 35 20-30 50-60 V. Strongly weathered 20-40 70 Eroded soils : subsoils resti ng on con- gravelly silt loam gravelly sandy loam gravelly clay loam 80-95 solidated material 30-80 20-25 25-40 40-60 60-70 VI. Primary soils under- laid by bedrock: Steep phases: fairly steep 60-80 Depth less than 1 foot... 1-2 feet gravelly sand steep 20-30 2-3 feet Stony: stony fine sandy loam. 70 70 70 65 60 35 10-40 stony sandy loam Miscellaneous nonagricultural material Type Description Rating in per cent Rough mountainous land 5-10 5-10 Steep slopes, eroded slopes, gullies, and canyon walls 5-10 1- 5 1- 5 Tidal lands 1- 5 1- 5 1- 5 Bul. 556] Index for Rating Value of Soils 39 SUMMARY Soils vary in their productive capacity. There is need for some method of comparing the relative productive capacity of different soils, especially in California where such a large number of widely divergent soil conditions exist. Such a soil rating or index would be useful in land classification and land evaluation. In this paper the term "index for rating soils" is used to express this relative rating. Soils having the highest productive capacity (from a study of the soil under field conditions) are rated at 100 per cent. The rating is based on the study of three general factors : A, charac- ter of the soil profile ; B, texture ; and C, modifying conditions. Index numbers are used for each group of factors based on 100 per cent expressing ideal conditions. The characteristics listed under factor A, character of the soil pro- file, are essentially those that determine the soil series. A grouping of the soil series of California is given according to their position in the six groups on the basis of factor A. Factors A and B together make up the soil type. Characteristics listed under factor C, modifying conditions, consist of drainage conditions, alkali, etc. The index is the product of the ratings given each of these three fac- tors, A x B x C, the ratings and the final index being expressed in per- centages. By the use of this method of rating soils, a large number of divergent types can be compared, or various tracts of land can be compared from the soil standpoint. The index for rating the agricultural value of soils presented in this bulletin can be used as a basis for judging soils. ACKNOWLEDGMENTS The author wishes to acknowledge the assistance and advice of Pro- fessor C. F. Shaw and Professor W. W. Weir in the preparation of this paper. Helpful suggestions were also made by Mr. J. H. Keith, County Assessor of Riverside County. 40 University of California — Experiment Station LIST OF SELECTED REFERENCES For the information of those who wish to secure more specific soil data, the follow- ing short list of books, bulletins, and circulars will be found to contain valuable information. In addition to those listed below, many other good books and publica- tions are available, but the publications listed below will be found of particular use to those who do not find time for extended reading on this subject. Practical in- formation on California soils can also be secured by consulting papers published in the American Journal of Agronomy, Proceedings of the American Soil Survey Asso- ciation, Soil Science, and other similar publications. Emerson, Paul. 1930. Principles of soil technology, vii + 402 p. Macmillan and Company, New York. Harris, F. T. 1920. Soil alkali, its origin, nature and treatment, vii 4- 258 p. John Wiley and Sons, New York. HlBBARD, P. L. 1931. Commercial fertilizers and soil fertility in California. California, Agr. Ext. Cir. 57:1-37. HlLGARD, E. W. 1912. Soils, iii 4- 593 p. Macmillan and Company, New York. HOAGLAND, D. R. 1930. Fertilizer problems and analysis of soils in California. California Agr. Exp. Sta. Cir. 317:1-16. Powers, W. L., and T. A. H. Teeter. 1922. Land drainage, iii + 270 p. John Wiley and Sons, New York. Robinson, G. W. 1932. Soils, their origin, constitution and classification. An introduction to ped- ology, vii + 390 p. D. Van Nostrand Company, New York. Shaw, C. F. 1927. Definition of terms in soil literature. Proc. 1st Intntl. Congr. Soil Sci. 4:38- 64. 1927. The basis of classification and key to the soils of California. Proc. 1st Intntl. Congr. Soil Sci. 4:65-104. 1927. Profile development and the relationship of soils of California. Proc. 1st Intntl. Congr. Soil Sci. 4:291-318. United States Department of Agriculture. Soil survey reports and maps (for the area in which the reader is interested.) 12 Weir, Walter W. 1932. Soil erosion in California: its prevention and control. California Agr. Exp. Sta. Bui. 538:1-45. 12 See Appendix for soil surveys completed in California. Bul. 556] Index for Rating Value of Soils 41 APPENDIX : SOIL SURVEY DATA IN CALIFORNIA There are two general types of soil surveys, the reconnoissance and the detailed, that cover portions of California. The extent of these sur- veys is shown on the map in figure 17. Reconnoissance surveys (shown on the insert in fig. 17) are generalized soil surveys with maps made on the scale of 1 inch to 2 miles or 1 inch to 4 miles. Seven such surveys were made during the period between 1913 and 1917, covering the major por- tion of southern California, the Sacramento and San Joaquin valleys, and the San Francisco Bay region. These show the soils in rather in- clusive groupings and rarely show bodies of soil less than 160 acres. They are being supplanted as rapidly as facilities permit by detailed soil surveys with maps made on the scale of 1 inch to 1 mile. On these maps the bodies of soils as small as 5 or 10 acres in extent are shown. All the soil maps are accompanied by reports giving a full description of the soil types shown with a discussion of their geographical distribution, relationship, and general utilization in that particular area. Where al- kali is present to any extent a separate alkali map is published. In addi- tion to the soil discussion, separate chapters are written covering the general description of the area, the climate, the agriculture, and often separate chapters on irrigation, drainage, and alkali conditions are in- cluded. In recent publications, there is also a technical discussion of the soils. These soil surveys serve as an inventory of the soil resources of the state and as a background for soil classification, soil evaluation, and other studies. Before extensive studies can be made on individual soil series or soil types, it is necessary to know in detail the characteristics of these soils, and also the location, the general environment, and the ex- tent of their occurrence. Basic studies on individual soil series or on groups of soil series are now in progress and in due time this soil infor- mation will become available in printed form. Completed soil surveys available in printed form are listed in table 5, those out of print in table 6, and those completed but not yet published in table 7. ten/ '•"•vo U - I — u_ W 7k*4* "\r1 I 1 RE CONNOISSANCE j / 1 AREAS #j\ fTAINITr / Ipsss-* LPIKt) ^V * — iMONO^k UMNC \ > \MeNoociNol I \ ClCl \ £?w V C0L \I l3 I iOLAljtt. KB! ^^C^f^; -p N vU& @l t& \ ^"santaVarbari 1 *\ io <4w> 25^ 4" J||j not ( g IIP Fig. 17. — Soil-survey areas in California shown by shading 1. Hanf ord 2. San Jose 3. Bakersfield 4. Sacramento 5. Stockton 6. Butte Valley 7. Colusa 8. Bedding 9. Modesto-Turlock 10. Pajaro Valley 11. Porterville 12. Marysville 13. Woodland 14. Livermore 15. Madera 16. Eed Bluff 17. Fresno 18. Merced 19. Ukiah 20. Healdsburg 21. Honey Lake 22. Pasadena 23. Eiverside 24. San Fernando 25. Anaheim 26. Los Angeles 27. Santa Maria 28. Ventura 29. El Centro 30. Grass Valley 31. Willits 32. Shasta Valley 33. Big Valley 34. Brawley 35. Eureka 36. Victorville 37. Lancaster 38. Palo Verde 39. Coachella Valley 40. Gilroy 41. Hollister 42. Auburn 43. Bishop 44. King City 45. Chico 46. Salinas 47. Oroville 48. Clear Lake 49. Placer ville 50. Santa Ynez 51. Paso Eobles 52. San Luis Obispo 53. Oceanside 54. Capistrano 55. ElCajon 56. Suisun 57. Dixon 58. Alturas 59. Lodi 60. Napa Bul. 556] Index for Rating Value of Soils 43 TABLE 5 Soil Surveys Available in Pamphlet Form, 1932* Number as shown on map (fig. 17) Area Anaheim Auburn Big Valley Bishop Brawley Chico Clear Lake Coachella Valley El Centra Eureka Gilroy Grass Valley Hollister Honey Lake King City Lancaster Los Angeles Lower San Joaquin Reconnois sance Middle San Joaquin Recon- noissance Date of survey 1916 1923 1920 1924 1920 1925 1927 1923 1918 1921 1923 1918 1923 1915 1924 1922 1916 1915 1916 Number as shown on map (fig. 17) 28 Area Oroville Palo Verde Valley Pasadena Placerville Riverside Salinas San Diego Reconnoissance San Fernando San Francisco Bay Reconnois sance Santa Ynez Santa Maria Shasta Valley Central-Southern California Reconnoissance Upper San Joaquin Reconnois sance Ventura Victorville Willits Woodland Date of survey 1926 1922 1915 1926 1915 1925 1915 1915 1914 1927 1916 1919 1917 1917 1917 1921 1918 * Can be secured from the Division of Soil Technology, University of California, Berkeley, California. TABLE 6 Soil Surveys No Longer Available for Free Distribution, 1932* Number as shown on map (fig. 17) Area Bakersfieldf Butte Valley Colusa Fresnot Fresnot Hanfordt Healdsburg Imperialt Imperial! Indiof Klamath Reclamation. Livermore Valleyt Los Angelest Lower Salinas Valley ... Maderat Marysville Mercedf Date of survey 1904 1907 1907 1900 1912 1901 1915 1901 1903 1903 1908 1910 1903 1901 1910 1909 1914 Number as shown on map (fig. 17) Area Modesto-Turlockf Pajaro Valley Portervillet Redding Red Bluff Sacramento Sacramento Valley Reconnois sance San Bernardino t San Gabriel t San Josef Santa Anaj Stocktont Ukiah Venturaf Yuma Date of survey 1908 1908 1908 1907 1910 1904 1913 1904 1901 1903 1900 1905 1914 1901 1904 * May be consulted at the principal public libraries in bound volumes of the Annual Field Operations of the Bureau of Soils. t Covered by more recent surveys. 44 University of California — Experiment Station TABLE 7 Soil Surveys Completed But Not Yet Published, 1932 Number as shown on map (fig. 17) Area Date of survey Number as shown on map (fig. 17) Area Date of survey 51 1928 1928 1929 1929 1929 56 57 58 59 60 Suisun 1930 52 Dixon 1931 53 1931 54 1932 55 El Cajon 1932 13m-9,'33