UNIVERSITY OF CALIFORNIA fa. COLLEGE OF AGRICULTURE STAT ' N FEB 9 1934 CIRCULAR NO. m Revised June, 1921 F? A p y THE USE OF LIME AND GYPSUM ON CALIFORNIA SOILS BY J. W. NELSON Much confusion exists in many minds with reference to the actual nature of lime and its use. The following brief statements are in- tended to clear up this confusion and to answer frequently recurring questions on the important subjects of lime and gypsum and their uses. THE NATURE AND FUNCTIONS OF LIME The term ' ' lime, " as we may employ it in the Agricultural sense, includes the following materials: (1) Burnt lime or quicklime (oxide of calcium), (2) hydrated or water-slaked lime (hydrate of calcium), and (3) ground limestone (carbonate of calcium). In addition a form of lime known as air-slaked lime is available, which may approach in chemical composition the ground limestone. Air-slaked lime results from the action of carbonic acid gas on water-slaked lime or from that of water and carbonic acid gas on burnt lime or quicklime. Either burnt lime, or hydrated or water-slaked lime, will change to air-slaked lime if allowed to lie in the open air long enough. The action is rather slow in the center of the pile, however, and thus it happens that so- called air-slaked lime frequently consists of a considerable proportion of quicklime, or of water-slaked lime, as the case may be, and is there- fore not so fully carbonated as one would expect. The total amount of air-slaked lime of the variety just described that is available on the market is very small. There is a form of air-slaked lime, however, that is available at present in considerable quantities. This form is a by- product of sugar refining, and in chemical composition is much more like ground limestone than the ordinary forms of air-slaked lime just discussed. This so-called "sugar house" refuse lime contains, in the dry state, from 70 to 80 per cent of calcium carbonate. It is usually in a very fine state of division and for that reason is superior to ground limestone, even though the latter may contain a larger proportion of actual calcium carbonate. University of California Southern Regional Library Facility Even in the agricultural sense, the term, lime does not include gypsum. The latter is an entirely different' Substance from the three named above, as will be explained later. Speaking with the exactness of the chemist, the term "lime" is applied only to burnt lime (quick- lime) or calcium oxide. Just how the three materials discussed from the agricultural point of view under the name lime are to be employed, and where one is to be preferred to the other, if at all, are questions which are answered below. Before going into a detailed discussion of the mission or function of lime in soils, it is well to state clearly the relative values in practice of the three different kinds of lime, (1) the burnt, caustic, or quick- lime; (2) the hydrated or water-slaked lime, and (3) the carbonate or the air-slaked lime. The value of these materials depends largely upon the amount of calcium oxide which they contain. Quicklime is nearly all calcium oxide. Hydrated or water-slaked lime contains less calcium oxide than quicklime, in about the proportion of 10 to 13. It takes 2643 pounds of hydrated lime to carry a quantity of calcium oxide equivalent to that carried by 2000 pounds of quicklime when both materials arr pure. Nevertheless, for practical purposes, they are not to be considered as very different, since they are rarely pure. Water-slaked lime, however, possesses advantages over ground lime- stone and quicklime in fineness of division and in purity. Thoroughly air-slaked lime, like sugar-house refuse lime and ground limestone, contains only a little more than half the amount of calcium oxide that the quicklime does and therefore about twice as much of either should be employed if it is to be used in place of burnt lime. If the ground limestone is not very pure, that is, if it contains less than 98 per cent of calcium carbonate, proportionately more should be used, according to its composition, than would be required if burnt lime were used. The same is true of sugar-house refuse lime. As the water-slaked lime has an advantage over the burnt lime, owing to its fineness of division, so, for the same reason, the sugar-house refuse lime has an advantage over the ground limestone. It must be remembered, however, in all these cases, that the total amount of calcium oxide obtained should be the first consideration when purchasing any of these materials. Other rules for making a choice depend upon conditions which are discussed below. Relative money values can be determined at any time with the help of the foregoing explanation of the comparative relations existing between the different lime materials. In this connection, the cost of handling larger quantities, and the additional freight rates involved, should always be taken into consideration in calculating the actual and relative cost of the different materials. The prices for lime vary in this state, to the knowledge of the writer, from $2 per ton up to $15 per ton, and there seems to be no uniformity of price based on actual lime content or on fineness of division. Local circumstances of various kinds usually set the prices. Ground limestone and sugar- house refuse lime have been selling at rates varying from $3.50 to $6.50 per ton, and, in most cases, very little of the other forms of lime is available on the market for agricultural uses. A list of some of the principal firms which sell lime in different forms may be obtained by addressing the College of Agriculture, Berkeley, California. Let us now consider the function of lime materials in soils. 1. Lime materials have the power of improving the crum-structure of clay and making it more pervious to water and air. Therefore lime makes clays and clay adobe soils looser, tends to prevent packing and baking, makes plowing and cultivating easier, and, in general, makes the soil physically a healthful medium for plant growth. 2. Lime materials tend to make "sour" soils "sweet." Speaking more correctly, they tend to change an acid soil condition to a less acid one. Acidity of soils is detrimental to the best growth of many agricultural crops. 3. Lime materials are necessary for the growth of beneficial bac- teria and other micro-organisms of the soil. Lime furnishes the element calcium, which is as essential to them as to the higher plants. It promotes a slightly alkaline condition, which is probably ideal for their development. By its physical effect, lime produces favorable air and moisture conditions for bacteria, as described above. . 4. Lime materials promote the normal decay of organic matter in the soil through their effects on the agencies of decay described above. The normal decay of organic matter in soil prevents the accumulation of certain poisonous materials that are detrimental to plant growth. 5. Lime will not neutralize the toxic effects of sodium carbonate or black alkali. THE NATURE AND FUNCTION OF GYPSUM Gypsum is the sulfate of calcium and therefore is not the same as ' ' lime, ' ' nor the same as any of the three forms of the latter that have been described. The only thing which gypsum has in common with the three lime materials named, as regards chemical composition, is that it contains the element of calcium. Its functions in soils may be briefly stated as follows : 1. Gypsum exerts a physical effect similar to that of lime on the clay and adobe soils (see above). 2. Gypsum, like lime, serves as a source of the element calcium (see above). 3. Gypsum, like lime, stimulates the beneficial soil organisms in the nodules on roots of leguminous plants, like the peas, beans, vetches, alfalfas, and clovers. 4. Gypsum does not make "sour" soil "sweet." It ivill not change an acid into a slightly alkaline sail as do the lime materials. Gypsum possesses no alkalinity, and therefore will not be of assistance in cases of, or act as a corrective to, "sourness" or acidity in soils. 5. Gypsum will neutralize the toxic effects of sodium carbonate or " black alkali." LIME VERSUS GYPSUM The question is frequently asked whether or not "lime or gyp- sum" will correct a certain difficulty in soils. This confusion of two distinct types of substances has done much harm, and the reader is asked to note carefully the statements made above with respect to each in order that errors may be avoided. As already stated, there is at least one very important function that lime performs in the soil which gypsum cannot perform. If soils need correction for acidity, the lime materials will serve but not gypsum. Too much emphasis cannot be placed on this distinction. In fact, to be on the safe side, the use of lime is advised in all cases where there is any doubt, except for neutralizing black alkali. The distinct and limited uses for gypsum are described below, however, to serve as a guide. NEED FOR LIME IN CALIFORNIA - , "-" >srr-s Generally speaking, it is likely that those areas in California re- ceiving more than twenty inches of rainfall, such as the northern coast counties, much of the Sacramento Valley and the Sierra Nevada and Coast Range mountains, have lost their lime from the upper few feet of soil. Other old upland soil deposits, such as the red hardpan lands of the Sacramento and San Joaquin valleys and the old marine^ ter- races and valley slopes in Santa Cruz and Monterey counties and southward along the coast to Mexico, are usually either in an acid or neutral condition. Lands subject to overflow, those occupying stream bottoms or recently formed valley slopes with less than twenty inches of rainfall, usually have lime well distributed through the soil mass and are less likely to need this constituent. All soils, however, receiv- ing large applications of organic matter should be examined period- ically for their lime requirements. LIME ON HEAVY SOILS No determination needs to be made to inform the owner of heavy land whether or not lime is necessary to improve the soil's structure in the ways described above. The decision both as to the amount to apply and as to the feasibility of applying it must be made on the basis of the cost of lime and the degree of "running together" or baking which is characteristic of the soil. From one to two tons of burnt lime or of hydrated lime, or from two to four tons of ground limestone, may be safely applied to improve the working qualities of heavy soils. Application may be made by means of one of the several types of lime-spreading machines or the lime may be deposited in piles and spread with a shovel. It should be harrowed in and if possible followed by sufficient moisture to distribute it through the soil mass one or more feet in depth. Burnt lime and hydrated lime are to be preferred to carbonate of lime for improving heavy soils if the cost will allow. The first two forms act more vigorously and more quickly. Applications of lime are best made after fall or winter plowing or one or more months prior to planting. This is particularly important if either burnt lime or hydrated lime is employed. LIME ON "SOUR" OR ACID SOILS ... If "sour" soils are also heavy clays or clay adobes, the recom- mendations made above for the use of lime on heavy soils should be followed. If they are loams, silts, or sands, ground limestone is usually to be preferred to the other forms of lime. On some of the acid soils in the northwest coast counties and in other localities in the state, the use of lime alone has apparently been of little or no benefit to alfalfa, but lime added with about two hundred pounds of sulfur per acre has given from one hundred to three hun- dred per cent increase in yields of alfalfa through a two-year period. Sulfur alone in the test above mentioned gave an increase of about thirty-five per cent for alfalfa. To test the soil for sourness or acidity, one may proceed as follows : Mix some of the surface soil to be tested and moisten thoroughly. Mold it into a ball of wet earth about three or four inches in diameter, care being taken that perspiration from the hands does not come in contact with the soil. Break the ball in two and on one of the broken surfaces place two strips of red litmus paper previously" moistened with clean boiled water. (Litmus paper, both red and blue, may be obtained in drug stores.) If possible, do not touch the moistened litmus paper with the fingers. Set the broken surfaces of earth together again and press tightly. Perform the same test with another ball of earth, but use blue instead of red litmus paper. Allow the balls of earth to lie undisturbed for half an hour ; then open, and if the red litmus paper has turned blue no lime is needed. If it remains red, and the blue litmus paper turns red, lime is needed and should be applied as above directed. If neither the red nor the blue litmus paper should change color, then the reaction of the soil is neutral and small applications of ground limestone, not to exceed one ton per acre, will be sufficient. WHEN AND HOW GYPSUM MAY BE USED Gypsum may be used with advantage on alfalfa fields to stimu- late growth. This is especially to be remembered in connection with alfalfa fields of several years' standing in which bare patches are found. An application of gypsum in such cases, not to exceed three hundred or four hundred pounds to the acre, along with fall-disking, will usually stimulate the plants and rejuvenate the field. The reason for this is believed to be that gypsum is a stimulant to the alfalfa plant itself and to the nitrogen-gathering bacteria that grow in the nodules on its roots. If lime is very expensive, as it may be in some districts of this state, gypsum, if much cheaper, may also be used as indicated above, to lighten heavy soils. Applications varying from one-half ton to one ton per acre may be used in such cases. Another, but more limited, use for gypsum consists in applying it to ' ' black alkali ' ' land to neutralize or make harmless the black alkali. In this respect gypsum cannot be replaced by lime. The quantities to be used in such cases depend on the amount of black alkali present in the soil. This will be determined for those interested, by the Cali- fornia Agricultural Experiment Station, upon application. Address College of Agriculture, Berkeley, California. NOTES ON LIMING 1. Lime should not be added to the soil at the same time as organic matter. Manure or cover crops should first be turned under and about a month later lime added to the surface and harrowed or disked in. 2. The fineness of ground limestone is an important factor in its availability and use in the soil. If ninety per cent passes through a forty- or fifty-mesh sieve it will be satisfactory for general use, at \ least for soils of light texture. *^ j 3. Quicklime and hydrated lime are usually the best forms to add to acid soils. These more active agents reduce the acidity quickly and soon stimulate plant growth. After their application ground lime- stone may be used. 4. The beneficial -results of lime are most marked where legumes are grown in the rotation and on soils well supplied with organic matter. 5. Field tests with annual crops, preferably legumes, as indicators, are the most reliable criteria for determining the amount and form of lime needed for the best results on the different kinds of soil and for the types of agriculture practiced. 6. A more dependable source and supply of the different forms of lime and gypsum at a less cost is greatly needed for the welfare of agriculture in most of California.