CALIFORNIA AGRICULTURAL EXPERIMENT STATION THE COLLEGE OF AGRICULTURE UNIVERSITY OF CALIFORNIA • BERKELEY Soil reaction, often expressed as pH, affects plant growth, influences soil microorganisms, and serves as an indicator of desirable and un- desirable soil conditions. Soil reaction should be considered in the choice of crops and in the selection and use of soil amendments and fertilizers. While this bulletin discusses these aspects, in a semitechnical manner, its main purpose is to supply long-needed information on the distribu- tion of acid and basic soils in California and the relation to soil series and to soil-forming factors, such as climate, rock material, and drainage. Since the soil reaction map— to be found in the pocket on the back cover— rests on soil surveys made over a period of decades, its accuracy is not uniform. Later surveys are more precise than former. However, the broad outlines of acid and basic soils are believed to be substan- tially correct. Ralph C. Cole, now Chief, Land Classification Section, United States Bureau of Reclamation, Region II, was formerly Assistant Professor of Soils, University of California. When holding this title, he began the study "Reaction of California Soils/' which summarizes a large amount of information contained in different soils surveys collected by the author and various members of the Division of Soils. This study was begun at the suggestion of Professor Hans Jenny, to whom the author now wishes to express his indebtedness for the suggestion and continued interest during preparation of the manuscript and the maps. REACTION OF CALIFORNIA SOILS Ralph C. Cole Soil reaction means the degree of acid- ity or alkalinity of the soil. This degree is indicated by a conventional term— pH— which denotes the concentration of hy- drogen ions in the soil— and a number which is known as its value. The pH values of most soils range from about 3.0 to 10.5, with pH 7 designating exact neu- trality. Values below 7.0 indicate acidity; those above 7.0, alkalinity or basicity. The pH scale is logarithmic, the concen- tration of hydrogen ions at pH 6.0 being ten times greater than at pH 7. The pH scale of soil reaction used in California by the soil survey is as follows : pH below 5.5 strongly acid soils pH 5.5-5.9 moderately acid soils pH 6.0-6.5 slightly acid soils pH 6.6-7.2 neutral soils pH 7.3-7.7 slightly basic soils pH 7.8-8.5 moderately basic soils (this is the range of soils having free lime) pH above 8.5. . . .strongly basic soils (soils (as high as 10) usually contain appre- ciable amounts of ex- changeable sodium) The pH values of the following com- mon substances are listed to make the sig- nificance of the soil reaction scale clearer: El u u o '55 c O := O D lemon juice pH 2.2-2.6 orange juice pH 3.4-4.0 sour milk (curdling). .pH 4.6-4.8 fresh milk pH 6.6-6.9 pure water pH 7.0 human blood pH 7.35 sea water pH 7.5-8.4 soap solution pH 8.7-9.9 1 Received for publication June 25, 1948. A thorough study of the natural factors of soil formation primarily responsible for the reaction of California soils indi- cates three— precipitation ; nature of par- ent material (rock) ; and drainage. The kind of natural vegetation also influences the pH of the soil. Since natural vegeta- tion itself is correlated with climate, par- ent material, and drainage conditions, it is more conveniently called a dependent factor. In some instances, the age of the soil must be considered; in areas of high rainfall, for instance, older soils tend to be more acid than recent soils. PRECIPITATION: low rainfall tends to produce basic soils; high rainfall, acid soils. During the processes of weathering and soil formation, the minerals of the origi- nal rocks (parent material) decompose. Under high rainfall and free drainage, the soluble bases are leached from the soil. Moreover, hydrogen ions from water and carbonic acid will replace adsorbed bases on the colloid particles and produce acid clays. In contrast, in areas of low rainfall the bases set free by weathering will re- main in the soil. Since calcium is the most abundant of the bases, and since its car- bonates are only slightly soluble, calcium carbonate will tend to form in arid soils. Accordingly, depending on the degree of leaching, some soils will be high in lime (calcium carbonate), and some will have lime only in the subsoils. Still other soils will be neutral and free of lime, or will possess varying amounts of acidity. Several good examples of California soils show relationships between amounts of rainfall and soil reaction. Table 1 illus- trates the dependency of pH on precipita- tion for residual soils derived from gra- nitic parent materials. The soils occur on [3] hilly relief and have good drainage. Un- der high rainfall the surface soils are strongly acid. The soils of the San Joaquin Series are formed on valley-filling materials of mixed composition. They are underlain by hardpan. According to table 2, the types occurring in the Sacramento Val- ley are more acid than those of the San Joaquin Valley. The soils of the Yolo sequence (table 3) are formed on recent alluvial materials from sedimentary rock sources. These well-drained soils occur on gently sloping alluvial fans or stream flood plains. They have developed under different conditions of precipitation. The Sorrento soils are slightly basic, with lime in the subsoil; the Yolo soils are neutral to slightly acid ; and the Corralitos soils are moderately to strongly acid. The broader aspects between soil re- action and precipitation in California are depicted in the generalized maps shown in figures 1 and 2. Basic soils are asso- ciated with regions of low rainfall, whereas acid soils are restricted to areas of high rainfall. The neutral and the slightly acid or slightly basic soils occur predominantly in the rainfall belt of 10 to 20 inches. The degrees of acidity or alkalinity are influenced also by parent material, topographic features, and age of the soil. PARENT MATERIAL (ROCK): variation in chemical composition of parent mate- rials causes variation in soil reaction from strongly acid to moderately alkaline. Parent material— that is, the rock or rock material from which the soil is de- rived—has a pronounced effect on deter- mining soil reaction. This is especially noticeable in regions of intermediate rainfall, whereas calcareous rocks tend TABLE 1 . Variation of Soil Reaction on Granitic Parent Material under Different Amounts of Rainfall Soil series Location Rainfall Average reaction Surface soil Subsoils Vista San Diego County San Joaquin County Santa Cruz County inches 10-15 18-24 40-60 PH 6.5 5.8 5.3 PH 7.1 Holland Holland 6.8 5.5 TABLE 2. Variation of Soil Reaction in San Joaquin Sandy Loam under Different Amounts of Rainfall Location Rainfall Reaction Surface soil Subsoils Tulare County inches 5-10 16-20 PH 7.1 6.0 PH 7.3 Sacramento County 7.0 [4] TABLE 3. Variation of Soil Reaction on Recent Alluvium from Sedimentary Rocks under Different Amounts of Rainfall Soil series Location Rainfall Average reaction Surface soil Subsoils Sorrento Western San Joaquin County inches 9-12 15-20 40-50 PH 7.4 6.2 5.5 PH 7.7 Yolo Colusa County (calcareous) 7.0 Corralitos Santa Cruz County 5.6 TABLE 4. Variation in Soil Reaction on Various Kinds of Parent Materials in Eastern Sacramento County Soil series Parent material Reaction Surface soil Subsoils PH PH 5.0 5.5 5.5 5.5 6.5 7.0 7.0 7.0 7.6 7.8 (calcareous) (calcareous) Amador Mariposa Auburn Pentz Ayar Light gray rhyolite tuff (Valley Springs formation) Brown slates Andesites Softly consolidated dull gray sandstone from andesite detritus (Mehrton for- mation) Marly shale to produce soils which have alkaline or neutral reaction. Sandstones low in bases give rise to neutral or acid soils. Generally speaking, the richer rock material is in base-forming minerals, the more leach- ing it will need to produce an acid soil. A good example of how pH of the soil varies with the type of parent material is found in the foothills of eastern Sacra- mento County. Five different soil series (table 4) occur adjacent to each other, within a mile or two. All are well drained, occurring on undulating or hilly topog- raphy. The rainfall varies from 18 to 24 inches, and the native vegetation consists of grass with scattered oaks. Within this physiographically and climatically uni- form region, soil reaction varies from strongly acid to moderately alkaline, in accordance with variations in the chem- ical composition of the parent materials. DRAINAGE: a high water table favors accumulation of lime and of white or black alkali, or both; a deep water table has no influence on properties of surface soil. The extent of drainage conditions in soils constitutes a hydrologic sequence association with the relief of the land. For the purpose of clarification, let us con- sider specific water table conditions on [5] Acid Ac id -neutral Neutral £?^^ Basic- neutral Basic gently sloping alluvial lands. Jenny 2 pic- tures such a condition by the following diagram : The sloping line represents the soil sur- face, and the horizontal dashed line the level of the water table. Under these con- ditions at W x the soil is under water; at W 2 the water table is within the zone of capillary rise of water to the surface; whereas at W 4 the water table is so deep that it has no influence on the properties of the surface soil. In arid climates the presence of a water table within distance of capillary rise of water to the surface enhances the amount of water that evaporates. This is accom- 2 Jenny, Hans. Arrangements of soil series and types according to functions of soil-forming fac- tors. Soil Science 61:375-91. 1946. Fig. 1.— Generalized distribu- tion of acid, neutral, and basic soils in California. (From C. B. Hutchison, California Agriculture. University of California Press, 1946.) panied by a concentration of soluble substances in the soil surface. The upward migration of salts largely, if not wholly, nullifies the effects of leaching by rainfall. Capillary rise favors the accumulation of lime and of white or black alkali, or both. A good illustration of the reaction changes of height to water table is shown by the coarse-textured alluvial soils of the Dinuba and Fresno series in the vicinity of Modesto in Stanislaus County. This is given in table 5. The Dinuba soils occur on land with variable distances to the water table, whereas the Fresno soils lie just above the overflow land where the water table is practically at the surface during the winter time and within 2 to 5 feet during the summer period. The presence of black alkali in the Dinuba (b) soils may place the reaction in the subsoil above pH 8.5. In the Fresno soils, the pH is nearly always above 8.5. It should be pointed out that the Dinuba soils, as defined in the soil survey, consist only of those designated as Dinuba (b). The soils designated as Di- [6] nuba (a), occurring under well-drained conditions with neutral reaction, have not yet been properly named. Similar drainage sequences but on fine- textured alluvial soils are found in north- ern Santa Clara County (table 6) . In this hydrologic sequence the Dublin soils occur in positions not affected by a water table ; the Clear Lake soils have a moder- ately high water table, and the Sunnyvale soils a very high water table. All of these soils are comparatively free of alkali. Clear Lake has lime in the subsoil; Sun- nyvale is calcareous throughout. Inten- sive pumping in the Santa Clara Valley has placed the water table much lower than when these soils were developed. COLLOIDAL PARTICLES ADSORB CHEMICAL ELEMENTS Soils contain clay and humus particles so small they cannot be seen individually, even by microscopic examination. These particles are called colloids. They have the power to adsorb or fix in exchange- able form chemical elements such as cal- cium (Ca) , magnesium (Mg) , potassium (K), sodium (Na), and hydrogen (H). These adsorbed elements determine a number of very important soil properties, such as structure, availability of plant nutrients, and, to a considerable degree, soil reaction. Sandy soils are low in col- loidal particles, whereas clay soils are high. In soils with neutral reaction, calcium is usually the dominant element on the clay particles. Such clay particles are de- signated as Ca-clay particles. In other words, Ca-clay particles give a neutral reaction. When lime (calcium carbonate) is present, soil reaction usually varies from pH 7.7 to 8.5, and the colloidal clay particles are virtually saturated with Ca. In arid regions, soluble salts, especially those of sodium, tend to accumulate in the soil. The sodium (Na) ions of the soil solution may displace the calcium ions on the colloidal clay particles. A Na-clay is then formed, usually with an increase in P H. Fig. 2. —Simplified map of an- nual precipitation in California. (From C. B. Hutchison, California Agriculture. University of Califor- nia Press, 1946.) Annual Rainfall 20- 100" [7] In humid regions, where soils are sub- ject to high rainfall and to leaching, the calcium ions on the soil colloids become displaced by hydrogen ions (H) of water, and the soils assume an acid reaction. Then H-clays are formed. Soil acidity is largely conditioned by H ions adsorbed on colloidal particles. TWO METHODS DETERMINE SOIL pH Accurate pH determinations are made most easily with a glass electrode. To 10 grams of dry soil is added 20 cc of dis- tilled water. After a period of several hours, during which the mixture is occa- sionally shaken or stirred, the glass elec- trode is inserted into the thick muddy portion of the soil suspension. The pH value, expressed in pH units, is then read off on the instrument dial. For approximations, colorimetric tests that can be conducted directly in the field are often satisfactory. Colored indicator solutions are added to dry or moist soil, and the resulting color is compared with a color chart indicating pH values or degree of reaction. The presence of calcium carbonate in the soil may be detected by adding to the sample a few drops of hydrochloric acid (one part concentrated acid to 10 parts water) or some other suitable acid, such as lemon juice, vinegar, or nitric acid. If the soil sample effervesces, the presence of carbonates is indicated. FERTILIZERS ALTER SOIL REACTION Pronounced effects on soil reaction re- sult from the use of commercial fertilizers. Different effects are due to differences in the acid-base balance of the fertilizers. Some fertilizers increase the acidity, others reduce it. Ammonium sulfate itself has a slightly acid reaction, and in the soil it tends to augment acidity. This effect may not be marked in one season, but when used continually over a number of years, the changes become pronounced. Sodium nitrate has a tendency to raise the pH. When used over a long period of time the reaction changes may be appreciable. Ammonia (NH 3 ) is a base, and it may alter the pH of the soil to a marked de- gree—at least temporarily. A variety of materials is used deliber- ately to alter soil reaction. To neutralize soil acidity, some form of lime, such as ground limestone, marl, sugar-beet lime, burned or hydrated lime is used. Calcium of the applied lime displaces the hydrogen ions on the soil colloids and thus reduces acidity. Gypsum, on the other hand, tends to lower the pH of alkaline soils. It also reduces the alkalinity of some alkaline soils. This is brought about by an ex- change of the calcium ions for absorbed sodium ions in the soil. On alkaline soils, sulfur is commonly added to lower the pH toward neutrality. In the soil, sulfur becomes oxidized to sulfuric acid, and this, in turn, neutralizes soil alkalinity. The amount of lime or sulfur to be applied to a soil depends on the degree of acidity or alkalinity on the one hand, and on the kind and amount of soil colloids (clays) on the other. Coarse-textured soils of low clay content need less lime or sulfur to change the reaction by any given amount than fine-textured soils contain- ing great amounts of clay. The data of Doneen and Lindsay 3 illustrate these conditions by specific ex- amples. Table 7 shows the effect of sulfur in lowering the pH of a light sandy loam soil in Kern County. At a depth of 6 to 12 inches, the acidity is so high (pH 4.4) that it is harmful to plant growth. Table 8 gives data from Doneen and Lindsay showing the effect of several years' use of ammonium sulfate on the pH of light sandy soils in Kern County. The adjoining untreated soils have pH 3 Doneen, L. D., and M. A. Lindsay. Effect of sulfur and ammoniacal fertilizers on potato soils in Kern County. February, 1946. (Litho.) [8 The reaction of clay particles in neutral soils, alkaline soils, and acid soils is shown in the following diagram. Ca Ca Mg Ca Clay particle Ca Mg Ca Ca Na Na Na Na Clay particle H Na Ca Na H H H Ca Clay particle Ca Na Ca Ca Ca H H Clay particle with Ca and Mg ions. The reaction is about pH 7.0. Neu- tral soils. Clay particle containing many Na ions and a few Ca ions. The reaction is basic (pH greater than 7.0). Alka- line soils, slick spots. Clay particle containing many H ions and a few Ca ions. The reaction is below pH 7.0. Acid soils. TABLE 5. Comparison of Soil Reaction as Influenced by Variation in Depth to Water Table (rainfall 10—15 inches; slope 9.5—2 per cent) Soil series Depth to highest water table Reaction Surface soil Subsoils Dinuba (a) feet 15 2-5 0-1 PH 6.5 7.2 9.3 pH 6.9 8.3 9.5 Dinuba (b) Fresno TABLE 6. Comparison of Soil Reaction as Influenced by Variation Water Table (sedimentary materials) (rainfall 10—20 inches; slope 0.5—2 per cent) in Depth to Soil series Depth to highest water table Reaction Surface soil Subsoils Dublin feet 7-10 2-5 0-1 PH 6.2 7.1 7.7 PH 7.1 8.0 8.2 Clear Lake Sunnyvale 9] values ranging from 7.2 to 7.6. The upper portions of the treated soil have become strongly acid. On the basis of experimental tests with various fertilizer materials, it was sur- mised long ago that the differences in the effects of fertilizers on soil reaction are due to differences in their acid-base balance. Materials containing an excess of basic elements (potassium, sodium, calcium, or magnesium) over the acid elements (nitrogen, phosphorus, sulfur, and chlorine) tend to reduce soil acidity, whereas materials with an excess of acidic over basic elements tend to increase soil acidity. Table 9, based on Pierre's work, ex- presses the relative acidity or basicity in terms of amounts of limestone or sulfur necessary to neutralize the fertilizer effect in soils; table 10 expresses the amounts necessary to neutralize the effect of com- mon soil amendments in soils. Depending on the rate of uptake of acid and basic constituents by plant roots, these relation- ships may be modified. As indicated above, the physical and chemical make- up of the soil also controls the influence of a given fertilizer on the pH of the soil. SOIL REACTION AFFECTS PLANT GROWTH AND SOIL MICROORGANISMS Soil reaction affects both plant growth and microorganisms, but the interrela- tionships are very complex and only parti- ally understood. Chemical elements like calcium, magnesium, sodium, potassium, and hy- TABLE 7. pH Values of Untreated and Treated Portions of a Potato Field in Kern County Depth from top of bed, inches pH in untreated portion of field pH in portion of field treated with 1,000 lbs. sulfur per acre 0-6 7.4 6.7 7.8 6.0 6-12 4.4 12-18 5.8 TABLE 8. Effect of Ammonium Sulfate on the pH of Soils on Three Ranches in Kern County Ranch A Ranch B Ranch C Depth in inches pHof soil Depth in feet pHof soil Depth in feet pHof soil 0-6 5.2 0-1 5.2 0-1 4.7 6-12 4.4 1-2 5.6 1-2 5.0 12-18 6.0 2-3 6.7 2-3 6.8 3-4 6.8 3-4 7.5 [10] TABLE 9. Relative Acidity or Basicity of Common Nitrogenous Fertilizers, and Amounts of Lime or Sulfur Required to Neutralize 1 Ton of Each (after Pierre*) Material Nitrogenous fertilizers : Ammonium sulfate . . Ammo-phos Urea Cottonseed meal Sodium nitrate Calcium cyanamide .... Per cent nitrogen Relative acidity Relative basicity Pounds lime (CaCOs) to neutralize 1 ton 21.1 36 2,249 11.0 18 1,097 46.6 27 1,688 6.76 3.6 194 16.4 9.5 22.0 20.0 Pounds sulfur to neutralize 1 ton 190 400 ♦ Pierre, W. H. Industrial and Engineering Chemistry. Analytical Edition 5:220-34. 1933. drogen, adsorbed on the colloidal parti- cles, have a multiple function. They influence soil reaction, they serve as nutrient elements, and they determine to some degree the physical characteristics of the soil. In addition, colloidal particles containing hydrogen ions (acidity) may exert a harmful effect on plant roots. Moreover, they may affect nutrition by modifying the soil solution and the rate of uptake of ions by plants. Arnon and Johnson 4 studied the ex- ternal effect of the hydrogen ion concen- tration on the growth of plants in water culture solutions where the plants could be well supplied with nutrients. They found that tomato, lettuce, and Bermuda grass plants grew fairly well between pH ranges of 4 and 8. At pH 3 the plants made no growth ; at pH 9 the growth was very poor, caused mainly by lack of absorp- tion of phosphorus. Arnon and Johnson found, however, that higher concentra- tions of calcium were required at pH 4 and 5 than at higher pH values. From this they concluded that at the extremes of the relatively wide physiologically suitable range of external pH between 4 and 8, good growth is possible only if special * Arnon, D. I., and C. M. Johnson. Influence of hydrogen ion concentrations on the growth of higher plants under controlled conditions. Plant Phys. 17:525-38. safeguards assuring a favorable supply of nutrients are observed. Plants may not be injured directly by moderate degrees of soil acidity or alka- linity. However, there are many indirect effects in soils that may be unfavorable to plant growth. In soils, under increasingly acid con- ditions, iron, aluminum, and manganese become more and more soluble. Iron and aluminum combine with soluble phos- phates to form very insoluble iron and aluminum phosphate compounds, and thus decrease the availability of phos- phorus to the plants. Furthermore, solu- ble aluminum even in very small amounts is toxic to plants. Manganese, although essential to plants in minute concentra- tions, becomes toxic if present in appreci- able amounts. As the adsorbed H ions (soil acidity) increase, the amount of calcium, and, to some extent, magnesium becomes less. The plant thus suffers a double disadvantage. Its increased phys- iological demand for calcium is met by a lowered supply. On the alkaline end of the reaction scale at high pH values, the phosphorus compounds are less soluble than at neu- tral reaction. The compounds of iron and manganese and some of the microele- ments precipitate and become unavail- [in able. At pH values above 8.5 appreciable amounts of sodium ions are replacing calcium on the colloidal particles, bring- ing about a very unfavorable physical condition of the soil. Reactions in California soils range from pH values of 4 (podzol-like soils near the Mendocino Coast) to pH values above 10 (alkali soils), the predominant range being from 5.0 to 8.5. Many crops grown in the state are capable of satis- factory growth over much of this range of soil reaction. However, there are some very important crops which have diffi- culty in making good growth in acid or alkaline soils. Alfalfa, sugar beets, sweet clover and some of the other clovers seem to prefer soils which are near neutral or slightly alkaline in reaction. They also do well in calcareous soils ; but they are sen- sitive to strongly acid soil conditions. Yields of these crops tend to drop off when soil reactions fall below pH 6.0, except in the presence of high amounts of exchangeable calcium. On the other hand, most tree fruits are able to grow well in soils with pH values as low as 5.0, but many suffer from iron deficiency (chlorosis) when the lime con- tent is high. It should be emphasized that crops can withstand greater extremes of unfavor- able soil reaction when the supply of available nutrients, especially calcium, is high. On most mineral soils having pH values below 6.0, alfalfa and sugar beets grow poorly, yet in the Sacramento-San Joaquin River Delta region there are areas of acid organic soils where very excellent yields of these crops are found. The organic soils are capable of supply- ing high amounts of calcium even at moderately low pH values. There are, however, fields in this area where soil acidity is so high that poor yields and even failures of sugar beets and alfalfa have been observed. Soil reaction affects not only crops but also microorganisms living in the soil. They, in turn, also influence crop growth. Usually the more beneficial microorgan- isms prefer soil reactions between pH 6.0 and 8.0. In strongly acid soils, legume bacteria fail to develop and function nor- mally. Nitrifying organisms also are sensitive to strongly acid conditions. On the other hand, certain fungi flourish in moderately to strongly acid soils. They do less well in soils which are neutral or basic. TABLE 10. Relative Acidity or Basicity of Common Soil Amendments Used in California and the Amount of Lime or Sulfur Required to Neutralize 1 Ton of Each (after Pierre*) Material Per cent sulfur Relative acidity Relative basicity Pounds lime (CaCOs) to neutralize 1 ton Pounds sulfur to neutralize 1 ton Sulfur 100.0 50.0 33.0 11.0 18.5 100 50 33 11 100 40-60 6,250 3,125 2,041 687 Sulfur dioxide Sulfuric acid Ferrous sulfate Gypsum Limestone 640 Sugar-beet lime 256-384 Pierre, W. H. Industrial and Engineering Chemistry. Analytical Edition 5:220-34. 1933. [12] Certain plant diseases are caused by soil organisms. A change in the soil re- action often is an effective control for such diseases. For instance, potato scab is caused by actinomyces organisms, and may be controlled by maintaining the pH of the soil at 5.5 or less. At this reaction the disease-producing organism becomes inactive, while the potato plant still main- tains growth. The disease which causes club root in cabbages and other crucifers is produced by a fungus that is inactive in neutral or alkaline soils, but flourishes in acid soils. Fortunately, most crucifers grow well in neutral soils and satisfac- torily in calcareous soils. SOIL REACTION MAP OF CALIFORNIA In preparing a soil reaction map of California, soils were arranged in five groups. Moderately to strongly acid soils (Symbol A).These soils are acid through- out the profile, with the surface soil often more acid than the subsoil. The pH values are usually between 5.5 and 6.0. Slightly acid soils (Symbol S). The surface soil varies in pH from about 6.0 to 6.5. The subsoil may also be slightly acid, or it may be neutral. Neutral soils (Symbol N). The re- action of these soils is in the vicinity of neutrality (pH 6.6 to 7.2). Soils having calcareous subsoils (Symbol +)• These soils contain free lime (calcium carbonate) in their sub- soils. Strictly speaking, the pH of a cal- careous soil depends on the carbon dioxide content of the soil solution, but for most soils containing lime it varies between 7.7 and 8.5. In other words, the soils of this group have moderately alka- line subsoils, whereas the surface soils are usually neutral in reaction. Soils having calcareous surface and subsoils (Symbol -\ — )-)• These soils are calcareous and therefore moder- ately basic throughout their profile. Many California soils are classified as alkali soils. Their reactions may be con- siderably higher than pH 8.5; in fact, some reach values of pH = 10 (sodium carbonate soils). It is impossible to de- lineate these areas on the soil reaction map. A very generalized soil alkali map appears on page 348 of "California Agri- culture," by C. B. Hutchison, and printed by the University of California Press, 1946. The data for the compilation of the soil reaction map found in the pocket at the back of this publication were taken from soil surveys made by the University of California and agencies of the United States Department of Agriculture. On the map of figure 3A each area is marked by a number which permits identification of the area with the aid of the soil survey key in figure 3B. In California approximately 380 dif- ferent soil series and over 1,100 types have been mapped. These have been estab- lished on the basis of soil properties, one of which is soil reaction. In general, the reaction of each soil series is confined to fairly narrow limits. There are, however, some soil series, especially older ones, which show considerable variation in pH. In recent soil surveys, more attention is being given to soil reaction than in earlier surveys. There are now a number of older soil series which have been separated into two or more series in accordance with differences in reaction. For example, the Yolo Series, as mapped in a number of older soil surveys, includes the following: Mocho— calcareous throughout Sorrento— calcareous subsoils Yolo— neutral Corralitos— moderately to strongly acid The original Hanford Series, mapped extensively in the San Joaquin Valley, now includes the following: Grangeville— calcareous throughout Hesperia— calcareous subsoils Hanford— neutral [13] The characteristic reactions of all the soil series mapped in California are given in table 11. These reactions will, in general, correspond to those listed in the various soil survey reports. Where there are discrepancies, the reactions listed in table 11 supersede those appearing in earlier publications. INTERPRETATION OF SOIL REACTION MAP In order to bring out more clearly some of the relationships between rainfall, parent material, and drainage conditions on the one hand, and soil reaction on the other, schematic transect graphs have AREAS SURVEYED AREAS NOT SURVEYED COUNTY LINES SURVEY LINES Fig. 3A.— Soil survey areas in California. The numbers refer to the key on the facing page. (From C. B. Hutchison, California Agriculture. University of California Press, 1946.) [14] been constructed. Four of them extend across the Central Valley and three across the coastal regions. Elevations and widths of bands do not represent specific magni- tudes. They are intended to show the rela- tive physiographic positions and the sequences of the various series. The transects demonstrate that, in general, soil reaction correlates with rain- fall, but it is materially modified and in places definitely dominated by the nature of the parent materials or the drainage conditions. The soils on the west side of the San Joaquin Valley are derived No. Area Date of survey No. Area Date of survey 7 8 9 io 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Around Fresno* Around Santa Ana* Hanford*.. Soledad Sheet* Lower Salinas Valley* Ventura* San Gabriel*. . . Imperial Valley* San Jose* Imperial* Indio* Los Angeles* Bakersfield* Sacramento* YumaArea,Arizona-California San Bernardino Valley* Stockton* Colusa* Redding* Klamath Reclamation Project Modesto-Turlock* Pajaro Valley* Porterville* Marysville* Woodland* Livermore Valley* Madera* Red Bluff* Fresno* Merced* Ukiah* Healdsburg* Honey Lake Pasadena Riverside San Fernando* Anaheim Los Angeles Santa Maria Ventura ElCentro Grass Valley Willits Shasta Valley Big Valley , Brawley 1900 1900 1 901 1901 1 901 1 901 1901 1901 1903 1903 1903 1903 1904 1904 1904 1904 1905 1907 1907 1908 1908 1908 1908 1909 1909 1910 1910 1910 19 1 2 I9I4 I9I4 I9I5 I9I5 I9I5 1915 I915 I916 I916 I916 1917 I918 1918 I918 I9I9 I920 I920 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 % 47 48 49 50 51 52 S3 54 55 56 57 58 59 60 61 62 63 6 4 66 67 68 69 70 7i 72 73 74 Eureka Victorville Lancaster ; . Palo Verde Coachella Valley Gilroy Hollister Auburn Bishop King City Chico Salinas Oroville Clear Lake Placerville Santa Ynez PasoRobles*,.. San Luis Obispo. Capistrano*. . .,. Oceanside* ElCajon* Suisun Alturas*. ., Dixon Lodi Barstow Contra Costa*. . Napa Pixley Delta Santa Cruz Visalia Wasco Bakersfield Kings County f. Tracy Newman t Stockton f LosBanosf Mendotaf Sacramentof. . . Santa Claraf. . . East Side Mesa . Colusa County t Santa Barbaraf. Coalingaf 1921 1921 1922 1922 1923 1923 1923 I923 1924 1924 1925 1925 1926 1927 1926 1927 1928 1928 1929 1929 1929 1930 1932 1931 1932 1932 1933 1933 1935 1934 1935 1934 1935 1936 1937 1938 1938 1939 1939 1940 1941 1941 1942 1942 1943 1943 * Out of print; may be consulted in the principal public libraries, t Not yet published. Fig. 3B.— Areas in California covered by detailed soil surveys. [15] TABLE 1 1. Soil Series of California Classified by Symbol According to Their Reaction Acolita + + Cachuma N Docas + + Hartley S Adelanto + Cajon + + Domino + + Henneke N Agate N Calera + + Dorado S Herdlyn + Ager + Caliente + + Drylyn + + Hesperia + Agueda + + Campbell + Dublin N Hillgate S Aiken S Camphora N Ducor + Hilmar S Alamitos N Canby + Dunnigan + Holcomb A Alamo + Capay + Holland S Aliso + Carlsbad S East Park N Holtville + + Altamont + Carpinteria N Edenvale + Honcut N Alviso + + Carrisalitos N Edison + Hopeton + Amador A Carrizo + + Egbert S Hornitos S Ambrose + Carson + Elder N Hovey + + Anderson N Castro + + Elkhorn S Huerhuero + Anita N Cayucos S Elna + + Hugo A Antelope N Chamisal S Empire A Antioch + Chamise A Escondido N Imperial + + Antone + Chino + Esparto S Indio + + Arbuckle N Chualar N Exeter N Arguello S Churchill + + Jalama S Arnold A Clear Lake + Fallbrook N Johnstonville + Atascadero S Climax + Farallone S Julian s Athlone N Coachella + + Farwell + Atwater N Cole S Feather s Keefers s Auburn S Colma S Felton A Kern + + Ayar + + Columbia N Ferndale A Kettleman + + Azule s Colusa + + Flournoy S Keyes A Cometa N Forgeus N Kimball S Bale s Commatti + Fort Bragg A Kirkwood N Ballard s Cone jo N Foster + + Klamath A Ballico A Contra Costa N Freeport + Kneeland A Barron S Coombs S Fresno + + Konokti S Bayshore + + Coquille A Bayside A Corning S Garey S La Branza + Baywood A Corralitos S Gaviota N Laguna s Bear N Correra Peat A Gazelle + + Lahonton + + Bear Creek S Cortina N Genevra + Landlow + Bella vista + + Cotati A Gila + + La Paloma A Bellegrave + + Cowell S Glamis + + Las Flores S Ben Lomond A Cropley + Glann S Las Posas N Berenda + Crow Hill s Gleason N Lassen + Berryessa + Cuyama + + Gloria N Laughlin S Bieber N Cuyamaca s Goldridge A Laveen + + Bishop + + Gorman S Leesville N Blucher S Daggett + + Gould N Lethent + + Bonsall N Danville N Grangeville + + Levis + + Borden + Delaney S Graton S Lewis + + Botella N Delano + ' Greenfield N Lindo + Bowers + + Delhi N Gridley N Lindsey + Brentwood + DeUo + Grimes + Lingard + Bryant + Denison S Linne + + Buntingville + Denverton + Hacienda + + Llano S Burns A Diablo + Hames S Lockwood s Butte S Diamond Spring S Hanford N Lodo s Dinuba + Harrington N Los Banos + TABLE 11 — -Continued Los Gatos S Oakley S Russell + + Tahoe S Los Osos A Occidental A Rydberg A Talmage S Los Trancos N Oceanview A Ryde S Tangair A Lost Hills + + Ohmer S Ryer + Tehama N Lynndyl + + Ojai N Tejon + Olcott N Sacramento + Temple + Madera + Olivenhain S Saunas + Tierra S Manzanita A Olympic A San Andreas S Tijeras + + Marcuse + Orestimba + San Emigdio + + Topo + + Marguerite N Orita + + San Joaquin s Traver + + Marina A Ortigalita + San Marcos + Tubac + Mariposa A Oxalis + + San Timoteo + + Tujunga N Marvin + San Tsidro s Tulare + + Maxwell + Pacheco + Santa Lucia s Tuscan N Maymen S Pachappa + Santa Rita + + Twin Oaks + Maywood S Pajaro A Santa Ynez N McClusky A Panhill + Saratoga s Ulmar + McCoy N Panoche + + Sebastopol A Underwood + McNabb N Pentz N Sespe + Melbourne A Perkins S Seville + Vallecitos N Meloland + + Permanente + + Shasta N Venado + + Mendocino A Pescadero + Shedd + + Venice A Merced + Peters N Sheridan S Vina N Merriam + Pinole S Sierra A Visalia N Merrill + + Pinto A Siskiyou S Vista N Metz + + Piper + + Sites A Volta + + Milagra N Pit N Sobrante S Milham + + Placentia N Solano + Wapato A Milpitas S Plainsburg + Soper N Wasioja + Mocho + + Planada + Soquel S Watsonville A Modoc N Pleasanton N Sorrento + Waukena + + Mohave + Pond + + Snelling s Westport A Mono + + Porterville + Spore N Whiterock A Monserate + Positas N Stacy + + Whitlock + + Montague + Prado + Standish + + Whitney N Montara N Preston + + Staten Peaty Willits A Montezuma + Purisima S Muck A Willows + Moreno + + Steinbeck A Woodrow + + Mormon + Ramada N Stockpen + Wright A Moro Cojo A Ramona N Stockton + Wyman N Mottsville A Raynor + Stonyford S Myers N Redding A Sunnyvale + + Yokohl N Rincon + Sunol N Yolo N Nacimiento + + Ripperdan N Sunrise + + Ysidora N Narlon S Roberts Muck A Superstition + + Ytias + + Niland + + Rocklin S Surprise N Yucaipa N Nord + + Rohnerville A Sutter N Norman + Rosamond + + Sweeney S Zaca + + Rositas + + Sycamore + Zamora N Oakdale N Rossi + + Zanja S Oak Glen N Rumsey + Symbol : A = Moderately to strongly acid soils. S = Slightly acid soils. N = Neutral soils. + = Soils having calcareous subsoils. + + = Soils having calcareous surface and subsoils. mainly from marine sedimentary rocks, whereas those on the east side are formed mainly on granitic rocks. Under compar- able rainfall and under good drainage conditions, the pH values of the soils from sedimentary rocks are usually higher than those from granitic rocks. In the valley trough, where drainage is sluggish and where the water table is high during a considerable portion of the year, the soils have higher pH values than do the soils on either side of the valley trough. Along the areas adjacent to the coast the rainfall is usually lower than at higher elevations on the slopes of the Coast Range Mountains. In a number of in- stances, however, the soils along the coast may be more acid than some of the soils occurring at higher elevations farther inland. The coastal soils are often sand and contain relatively few bases. Consequently, they are readily leached and easily become acid. Some of the soils in the upland areas are derived from cal- careous shales. Water percolation is slow ; hence, these soils may have higher pH values. The transect maps will be found in the pocket on the back cover. SUMMARY Soil reaction is the degree of acidity or alkalinity of the soil. It is usually ex- pressed quantitatively in pH units. The degree of soil reaction is dependent mainly upon three important soil-form- ing factors : climate, parent material, and drainage. In general, soils in areas of high rainfall are acid and those in areas of low rainfall are basic. Soils formed from parent materials high in calcium, magnesium, potassium, and sodium are less likely to be acid than those formed from parent materials low in these ele- ments. Soils in arid areas formed under conditions of high water table are more basic than those formed where drainage is adequate. The nature of the soil reaction often affects the type of plants that can be grown. There are certain very important crops, such as alfalfa, sugar beets, and some of the clovers, which do not grow well in moderately acid or strongly acid soils, but produce very well in soils which are highly calcareous. On the other hand, lemons and a number of other tree fruits are sensitive to soils high in lime, but do well in moderately acid soils. Soil reaction also affects the nature of the microorganisms within the soil. In general, bacteria and actinomyces grow well in soils with reactions near neutral to basic, whereas fungi prefer soils which are acid in reaction. Some of these micro- organisms, such as nitrifying bacteria, do valuable service to plants, whereas a num- ber of plant diseases are caused by soil microorganisms. In some cases the con- trol of the disease can be effected by control of the soil reaction. The reaction of the soil can be altered by the use of amendments. The principal amendments are lime to reduce acidity and sulfur to increase it. The soil reac- tion of some soils is materially altered by the application of certain fertilizers. For instance, ammonium sulfate increases the acidity of sandy soils. The distribution of the soils in Cali- fornia, according to their reaction, is shown on a series of maps in the pocket on the facing cover. This distribution is mainly correlated with the amount of rainfall, but there are local variations dependent on other factors, such as parent material and drainage conditions. 8m-4,'49(B1689) [18] MODERATELY TO STRONGLY ACID SLIGHTLY ACID NEUTRAL CALCAREOUS SUBSOIL CALCAREOUS SURFACE AND SUBSOIL MISCELLANEOUS SOIL MATERIAL, INADEQUATE DATA OR UNSURVEYED main UNIVERSITY Oh L.AUFORNk/% wher LIBRAR main COLLEGE Ob AGHK :Ul Ti ?rc able Davis cond sedin than valle and i a co] soils soils Al ther. So alkal press degn main ingf, drain high of lo from magn less 1 from menti condi basic is ad< Th affect grow] crops some well i soils, are hi lemor are sc well i : : i • "K 4-1-4 -■&% _|J T I- | I ' ' ' 4^*iHf^rM ifu^-j i — i — i — rn — i — gt i i- t _ |-T -r H tr_^_; 4^1-,-^-,- L-I-L4- .j r j r 4-_l_j-j-4-4-H-*-Hrr _i i i — J — i — i — '— -i — i- +--.— i — 1 — 1~ ! I ,,, ! , I I | M | I D ' I C I ' 4- ■L--+-I "I 1 .j_r i i i i« -i-i- -t-, _l _ J i L 4 ~i J, ~i 4 4-h --r-|-H- ' :ii-'_U-i— 4-U ! -J-uJ- y_L ' l s '".i-'l'Jir-L."J ' h-H- L --4- i --T-r "'""'" + cL-i^-lJrri.j^ 4 U-i-j-i-t^-i-^-i-i-rfi-'r-i-i-i-i-: -M4-!K J ^-:-^r-H-:-M4-!-v^- , rrn-- | r;-r^^ .16 |. -I- i -4 4-I- + -, ' -J- ; — f — i — | — — s - , 'f '' ' 'i L- 1 - 1 I I i ' ! L tIe L h -I a V .J-lJ-inhi-H-t-rr-'-^^l .J.j.I.lILIj illllf'i!'!"^ ..-iJ-J-L-tXi.. 3*9 man whe mai able corn sedi thai vail and a c soil soil I the alk pre de£ ma ing dn hi^ of frc rru les frc m< CO ba is T^n >~^ i |i i i i — r~7 \ L 4 t , f , -i t - | - H ' + -r i^-r- ^ J i —I —st- -r -I - - t 4 /r- -r --ff-t-i-n t 4 ,Ej SAN FRANCISCO/^on ^SffAKLANO V" af gr cr so w a i le a i w LIBRARY COLLEGE OF AGKICULTURE DAVIS J-rr I 1 1 I i i i j 4 t 4-- r t_^a-|->-l--f-r- fj- **4#±-- .t.-.- ,*v* fyC % V. % V, '* •< AAs/ a aa x^v^r^Tv" /^ttv v ; > a / 'Tx X V > V */' * >-a \/ j ><. >V N A X N / / \ /x ^A* A / a -v* 'N A4/; w?&: 4? * As >C /1v >A A V v 7A *> -x/v ,A^- . / .A v /\ / \, s* AAV » 'V~* LOCATION AREAS V -^ V A 4' VA S y /\ ? + *■ V^ /A V A A v A \ / * A. A / #4&A.A a / x m. 7 ■ ■^■ X 7^JIFA / A x h| Hr > a/ f^/x / \/ ; K%:#^ A>A™ Fa > A X| / A > AAA A^yAAA^AAAA-^ .",: ^ — T~r / A X /N/ / N V / n/ / X v > / >./ x / UBRARy college of agriculture DAViS / e \* *, / CROSS SECTION OF THE SACRAMENTO VALLEY (near Colusa] Annual rainfall at Biggs 22.10 ' " " " Colusa 15.12' Hugo A Maymen S Henneke N Ven- ation Contra Costa N Ayar + + ramento River ther River Aiken S Mariposo A Corning S o I/O s. HoncutN WymanN San Joaquin S Redding A Yolo N Zamora N Gen- Willowst Sacramento + Sycamore + Columbia N Marvin t Stockton + Gridley N Colum- bia N PARENT MATERIAL Sedim'ntory- Serpentine Serp- entine Sedimen- tary Mixed Sedimentary Mixed Mostly basic igneous Mixed Mostly basic igneous Mixed Basic igneous slates DRAINAGE CONDITIONS Good High water table Good High water table Subject to overflow Good Perched water table during wet season Good ALKALI Free Mod. to strong white olkali Spotted alkali conditions, mostly white alkali Free Neutral Calcareous subsoil Calcareous throughout Slightly acid Moderately to strongly aci UNIVERSITY OF CALIFORNIA LIBRARY CROSS SECTION OF THE SAN JOAQUIN VALLEY (near Stockton) COLLEGE OF AGRICULTURE DAVIS Annual rainfall at Stockton 14. 1 l' " " " Antioch 12.25' Los Osos S Altamont + Denver- ton ♦ Monte- zuma + Old River Middle River San Joaquin River San Joaquin S Redd- ing A Whitney N Pentz N Peters N AmadorA Sorrento + Rincon + Ambrose + Solono + Marcuse + IT \J lr~ DELTA AREA Mucks and peats A Ryde S Columbia N Sacramento + Stock- ton + Dinuba + Delhi N Hanford N PARENT MATERIAL Sedimentary Organic materials and Mixed materials Mostly basic Granitic Mixed Sedimen- tary DRAINAGE CONDITIONS Good High water table Subject to overflow High water table Good Perched water table during rainy season Good ALKALI Free Usually free Strong white alkali Some spots of alkali, mostly white alkali Spotted white 6 black alkali Usually free Free Neutral Calcareous subsoil Calcareous throughout Slightly acid Moderately to strongly acid j>a va^a,<>:v >^*a; S--v V V T'V A ft < A V A\ A/ X \A \ V \ / \ ' \ A* 'A * y v/ \ X V * X A ,\ > /\ A, A "V * \x ;< V^/yV x x> v y \ ^AAAl \ _,;*# > > A ,Y *\ y v > v \/ \ / ■\V-A- \ A V^ X V v- V < * v* y \ / \ / ^ X.X V \ >^ N v \ X \ > V >\<> V \ ar '* fo X a vr v \yx* v V ,A ,A vs/V V, V LOCATION OF AREAS \^ X 1T \y \ /V x >jt$: x > V v v V v X X v > o A '* * A s A N / JN ' •\ X ^ X X >^A x ^v V > >' \a/V yK* v > V >\ A X ■<\ ►-^-C^, A^o X V A V=> 4^" V. > X< AA V a'v X ^ X 1 A \*/ J A ^A, X , •* < v Xt > > X x > A\ > >»A > AT X V \< **1 E A N S3Q Tz.2. I948//949 CROSS SECTION OF THE SAN JOAQUIN VALLEY (near Bakersfield ) Annual rainfall at Bakersfield 6.12 " " " Maricopa 5.69' Kettleman + + Delano + Adelanto + Madera + Cuyama ++ Caliente ++ Panoche + + Lost Hills + + Merced + Temple t Sacramento + Tulare + + Traver + + Pond + + Chino + Fresno + + Foster +t Cajon + + Hesperia + Exeter + PARENT MATERIAL Sedimentary Mixed Granitic Mixed Sedimentary DRAINAGE CONDITIONS Good Good High water table Subject to overflow High woter table Foster soils have tlucuating water table Others good Good ALKALI Occasionally some white alkali Panoche- Occasionally some white alkali Lost Hills - Usually some white alkali Spotted alkali, both white and black Pond- Strong, white and black alkali Chino - Spotted alkali- white and black Foster and Cajon - Spotted alkali - white and black Others usually free Free Occasionally some white and black alkali Free Calcareous throughout Calcareous subsoil UNIVtKSI IT OF CALIFORNIA ooixECEo^icijLTORr CROSS SECTION OF THE SAN JOAQUIN VALLEY (near Merced) Annual rainfall at Merced 11.81 ' " " "Newman 10.06' a. c '5 or Whitney N Pentz N Peters N Amador A Vallecitos N Altomont + Denverton + ^ g Redding A Dinuba + Atwoter N Delhi N Hanford N Greenf'ld N Son Jooquin S Sorrento + Rincon + Esparto N Orestimba + Rossi + + Woukena+ + Col'mbia N Sac'to + Temple + Merced + Pond + + Fresno** Trover +♦ PARENT MATERIAL Sedimentary Sedimentary a Granitic Mixed Granitic Mixed Sedimentory DRAINAGE CONDITIONS Good High water table High water table Subject to High water table Fluctuat- ing water table Good Perched water table during rainy season Good ALKALI Free Usually free Usually free Orestimba, some white alkali Rossi-Wauk., strong, white & black alkali Spotted alkali, white a block Strong alkali, white a black Spotted alkali, white a black Free + = Calcareous throughout t = Calcareous subsoils N = Neutral S = Slightly acid A = Moderately to strongly acid CROSS SECTION OF COASTAL AREA (near San Diego) Annual rainfall at San Diego 10. 30 ' ,, „ ".. £/ Ca J° n 13.92' Cuyamaca 39.87" Marino S Elkhorn S Aliso + Merriam ♦ Huerhuero + Alviso + + Cajon + + Hanford N Greenfield N Botello N Sorrento + Agueda + + Aliso + Merriam + Huerhuero + Las Flores S Olivenhain S Redding A Linne + + Ayar + + Altamont + Diablo + Las Posas N Escondido N Vista N Fallbrook N Holland S-A PARENT MATERIAL Mixed Granitic, Sedimentary Mixed Sedimentary Basic igneous, Gronitic Granitic DRAINAGE CONDITIONS Good Perched water table during rainy season High water table Good Perched water table during rainy season Good ALKALI Free Strong white S block alkali Usually free Free N = Neutral + = Calcareous subsoil ++ = Calcareous throughout S = Slightly acid A = Moderately to strongly acid UN1VERSMY Ot cAL.*rORN*A L1BRAR GOLLECE OF AGRICULTURE DAVIS l948l'S49 CROSS SECTION OF COASTAL AREA (near Davenport and San Jose) Annual rainfall at Santa Cruz 26.13" " " " Ben Lomond 55.91" " LosGatos 29.62" San Jose 13.93" " " " LickObserv. 27.47' Tierra A Santa Lucia A Holland A Sheridan A Felton A > CE o o _l Ben Lom- ond A Pajaro A Arnold A Hugo A Los Gatos A Milpitas S Cupertinos Saratoga S Azule S > ir I ~~~^^___° , Dublin N Sorrento + Yolo N Zamora N Pleosonton N Mocho + + Milpitas S Montara N Climax + Berryessa + Altamont + Vallecitos N r Watson - ville A Lock- wood A ElkhornA PARENT MATERIAL Mixed, Sedimen- tary Mixed Sedi- mentary Granitic, Mica Schists Mixed, Sedimen- tary Sedimentary Basic Igneous, Sedimentary DRAINAGE CONDITIONS Watsonvi Perched during w Others, le S Tierra w't'r table et season good . Good Fair Good Fair Good ALKALI Free Usually free Free N = Neutral t - Calcareous subsoils ** = Calcareous throughout S = Slightly acid A = Moderately to strongly acid UNIVUOl M Of CALIFOKfdA LIBRARY CROSS SECTION OF COASTAL AREA (near Santa Barbara) OOLLECE Oh AGRICULTURE DAVIS Annual rainfall at Santa Barbara 18.90" San Marcus Pass 30.66' Los Alamos 15.84' \^ o Nacimiento ++ Sespe + Gaviota N Santa Lucia S"A Maymen S Rough land |^ o Rough broken land Santa YnezN Bal- lard S Metz + + Santa Ynez N Ballard S Cach- uma S Chamise A Milpitas S Monte - zuma + Aliso + Olivenhain S Marina A Milpitas S Montezuma + Alviso ++ Clear Lake * Agueda + + Sorrento + Yolo N Mocho + + PARENT MATERIAL Mixed (mostly sedimentary) Sedimentary Mixed (mostly sedimentary) Sedimentary Mixed (mostly sedimentary) DRAINAGE CONDITIONS Perched water table during wet season High water table Good Perched water table during wet season Good Fair Good Fair Perched water tble during wet season ALKALI Free High Variable white alkali Usually free Free Usually free Free N = Neutral + = Calcareous subsoils t+ = Calcareous throughout S = Slightly acid A = Moderately to strongly acid