THE EFFECTS OF ALKALI ON CITRUS TREES. W. P. Kelloy & E. E. Thons THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES UNIVERSITY OF CALIFORNIA PUBLICATIONS COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA THE EFFECTS OF ALKALI ON CITRUS TREES BY W. P. KELLEY AND E. E. THOMAS BULLETIN No. 318 JANUARY, 1920 DIVISION OF SUBTROPICAL HORTICULTURE COLLEGE OF AGRICULTURE BERKELEY, CALIFORNIA UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1920 EXPERIMENT STATION STAFF HEADS OP DIVISIONS DAVID P. BARROWS, Ph.D., LL.D., President of the University. THOMAS FORSYTH HUNT, Deaii. EDWARD J. WICKSON, Horticulture (Emeritus). WALTER MULFORD, Forestry, Director of Resident Instruction. HERBERT J. WEBBER, Director Agricultural Experiment Station. B. H. CUOCHERON, Director of Agricultural Extension. HUBERT E. VAN NORMAN, Vice-Director; Dairy Management. JAMES T. BARRETT, Acting Director of Citrus Experiment Station; Plant Path- ology. WILLIAM A. SETCHELL, Botany. MYER E. JAFFA, Nutrition. CHARLES W. WOODWORTH, Entomology. RALPH E. SMITH, Plant Pathology. J. ELIOT COIT, Citriculture. JOHN W. GILMORE, Agronomy. CHARLES F. SHAW, Soil Technology. JOHN W. GREGG, Landscape Gardening and Floriculture. FREDERIC T. BIOLETTI, Viticulture and Enology. WARREN T. CLARKE, Agricultural Extension. JOHN S. BURD, Agricultural Chemistry. CHARLES B. LIPMAN, Soil Chemistry and Bacteriology. CLARENCE M. HARING, Veterinary Science and Bacteriology. ERNEST B. BABCOCK, Genetics. GORDON H. TRUE, Animal Husbandry. FRITZ W. WOLL, Animal Nutrition. W. P. KELLBY, Agricultural Chemistry. H. J. QUAYLE, Entomology. ELWOOD MEAD, Rural Institutions. H. S. REED, Plant Physiology. L. B. BATCHELOR, Orchard Management. J. 0. WHITTEN, Pomology. FRANK ADAMS, Irrigation Investigations. C. L. ROADHOUSE, Dairy Industry. F. L. GRIFFIN, Agricultural Education. JOHN E. DOUGHERTY, Pbultry Husbandry. S. S. ROGERS, Olericulture. L. J. FLETCHER, Agricultural Engineering. EDWIN C. VOORHIES, Assistant to the Dean. CITRUS EXPERIMENT STATION DIVISION OF AGRICULTURAL CHEMISTRY W. 1'. KELLEV *A. B. CUMMINS E. E. THOMAS S. M. BROWN Resigned June 1, 1911). THE EFFECTS OF ALKALI ON CITRUS TREES : BY W. P. KELLEY AND E. E. THOMAS INTRODUCTION It is generally believed that citrus trees are especially sensitive to alkali. One of the best known investigations on the effect of alkali on citrus was published by Loughridge in 1898. 1 In this paper it was pointed out that orange trees may be severely injured by the use of saline irrigation water. From studies on certain groves near Corona, California, it was found that severe injury had been produced a.s a result of irrigating with saline water from Lake Elsinore for a period of from three to four years. Analysis of the water showed it to contain 917 parts per million sodium chloride (common salt), 377 parts per million sodium sulfate (glauber.salt), and 391 parts per million sodium carbonate (black alkali). Loughridge concluded that the injury to the trees was due directly to the corrosive action and puddling effect of the black alkali and indirectly to the antiseptic action of the sodium chloride on the bacterial processes of the soil. The effects were more pronounced in certain groves than in others. Inherent differences in the soil apparently exerted an influence on the depth to which the water penetrated and, therefore, caused the salts to accumulate in greater quantities in the upper layers of the soil of certain groves than of others. On the whole, the effects were roughly proportional to the concentration of the alkali salts that had accumu- lated in the zone occupied by the roots of the trees. The results of this investigation indicated that citrus trees are quite sensitive to alkali, and that the length of time a given supply of saline irrigation water may be used without producing injury depends mainly on the rate the injurious constituents accumulate in the layers of soil occupied by the roots of the trees. In 1900 Hilgard- pointed out that citrus trees are especially sensi- tive to sodium chloride. He called attention to the previous work at * Paper Xo. 53, University of California, Graduate School of Tropical Agricul- ture and Citrus Experiment Station, Kiverside, Calif. 1 Effect of Alkali on Citrus Trees. Annual Keport, Calif. AT. Exp. Sta. 1897-8, pp. 99-113. 2 Nature, Value and Utilization of Alkali Lands. Calif. Ar. Exp Sta Bull 128 (1900), p. 28. 209908 306 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Corona in which it had been found that 2520 pounds per acre of sodium chloride distributed through the soil to a depth of four feet, caused an orange tree to become completely leafless, while another tree nearby, where the soil was similar in other respects, but contained only 720 pounds per acre of sodium chloride, w r as much less severely injured. "Here it is apparently the excess of common salt to which the difference is due." In 1901 Loughridge 3 called attention to the extreme sensitiveness of the lemon tree. lie said: "The lemon seems to be the least tolerant of all of the fruit trees, for it was stunted by 1440 pounds common salt per acre, distributed through four feet depth, and was killed bj" 1900 pounds combined with 1900 pounds carbonate of soda." In harmony with the conclusions of Loughridge and Hilgard, recent investigations by the writers have shown that different varieties and species of citrus trees are quite sensitive to alkali, especially so in the case of the lemon, and that after a few years irrigation with saline water, both lemon and orange trees may be severely injured. Again, it has been found that the effects produced by a given supply of impure irrigation water may, for a time at least, be extremely variable even in different portions of the same grove. Part of this variability, as shown below, is probably due to differences in the depth to which the water penetrates, which in turn affects the rate at which the salts accumulate in the root zone. Experience in various localities has shown that, under certain conditions, continued irrigation with comparatively pure water also tends to hasten the accumulation of injurious amounts of soluble salts. Several hundred thousand acres located in different parts of Califor- nia, which were free from injurious amounts of alkali previous to the introduction of irrigation, have since become veritable alkali lands. Seepage, together with a rising water table incident to over-irrigation, have been the principal means by which the salts have been brought up from below and deposited near the surface. Small areas of citrus groves have already become heavily charged with alkali by this means. In the course of investigations on the nutrition of citrus trees, we have devoted considerable study to certain phases of the alkali prob- lem. Early in this work, it became evident that the existing state of knowledge was inadequate. The symptoms of alkali injury have not been recognized clearly. The relations of fertilizers to the problem, and especially the effect of applying irrigation water containing alkali salts, are inadequately understood and appreciated. s Tolerance of Alkali by Various Cultures. Calif. Agr. Exp. Sta. Bull. 133 (1!MU), pp. 14-Ki. BULLETIN 318 THE EFFECTS OF ALKALI ON emirs TREES 307 It is commonly held that alkali injury is mainly, if not entirely, due to excessive concentration as such. In the course of this work, it has become evident, however, that injury may be produced under certain conditions where the total concentration is relatively low. The data obtained in a study of this phase of the subject afford the basis for an interesting hypothesis which will be presented elsewhere and further work is in progress. The discussion in this bulletin will be confined mainly to the effects of excessive concentration. As this work has progressed, it has become increasingly evident that many of the citrus growers of California have not sufficiently grasped the significance of alkali in citrus culture. Especially is this true in regard to the bearings of impure irrigation water on the accumulation of alkali in the soil. Fortunately, a large percentage of the citrus soils was free from alkali previous to the introduction of irrigation and very much of it still remains free. There are con- siderable areas located in several districts, however, where harmful amounts of alkali have accumulated as a result of applying saline irrigation water and still other areas, not yet seriously injured, where alkali is accumulating at present as a result of orchard practices which, if continued, will ultimately produce injury. This bulletin will be devoted to a discussion of results obtained in connection with a study of a considerable number of citrus groves in different localities in California. The investigations reported herein deal mainly with the effects of alkali rather than with means of over- coming the injury. It is undoubtedly a matter of practical importance for citrus growers to be able to r< cognize the effects of alkali and especially to appreciate the relationships between existing orchard practices and the accumulation of alkali. Unfortunately, the present state of knowledge does not yet make it possible to predict with as great a degree of certainty as is desirable, what the effects of a given amount of alkali will be, or how long a given saline irrigation water may be applied before producing injury. The extreme variability of soils and the inadequacy of knowledge concern- ing the fundamental relationships between salts and soils, and salts and plant growth, add to the difficulty. Despite these facts, informa- tion of some practical importance has been obtained. The investigations reported herein should be looked upon as being preliminary to a study of methods of combating alkali in citrus groves. It is hoped that fhis discussion will enable citrus growers to recognize the effects of alkali, to appreciate the seriousness of alkali in citrus culture, to apprehend more clearly the relationships between irrigation and the accumulation of alkali, and to see that the applica- DIVl&ON OF SUblROPICAl HORTICULTURE COlUGt OF AGRICULTURE btRKlY. CALIFORNIA 308 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION tion of certain fertilizers, especially nitrate of soda, may, under certain conditions at least, bear a very important relation to the accumulation of alkali. With this knowledge, it is hoped that practical citrus growers will be able to adjust their irrigation and fertilizer practices in such a way as to retard the further spread of alkali and thus prevent its accumulation in many groves that have, as yet, not been seriously injured. SYMPTOMS OF ALKALI INJURY Different varieties and species of citrus trees are affected differently by alkali. Lemon trees show the effects by a pronounced yellowing of the margins and burning of the tips of the leaves, followed by unusually heavy shedding of the leaves in the latter part of the winter and spring. The subsequent new growth may appear to be quite normal and vigorous for several months, but later a large portion of the leaves turn yellow in irregularly shaped areas around the margins and fall excessively. In the presence of excessive concentrations of salts, especially chlorides, complete defoliation may take place. Mottle leaf frequently occurs, and sometimes chlorosis. Both the quality and quantity of the fruit are impaired. Orange trees also show the effects of alkali in different ways. On certain soils, mottle leaf is one of the first symptoms. In some locali- ties, the older leaves assume a brownish hue and tend to curl slightly. Kather sudden defoliation takes place, especially when excessive amounts of chloride occur, followed later by a profuse growth of new shoots. The leaves of the new growth are likely to be undersized and paler in color than normally. With especially high concentrations of sulfates and bicarbonates in the soil, orange leaves become chlorotic and strikingly similar to that condition referred to by Hilgard 4 as occurring on highly basic soils. The smaller twigs may be killed. Frequently the leaves are abnormally small on one portion of a tree, and full-sized 011 others. Premature shedding of the leaves takes place with both oranges and lemons affected by small amounts of alkali, which may be pro- tracted throughout the greater part of the winter months, thus greatly reducing the number of leaves remaining on the trees at the close of the dormant period. Navel oranges are more sensitive than Valencias, and Eureka lemons more sensitive than Lisbons. In general, lemon trees are more sensitive 1 than orange trees. Neither orange nor lemon 4 Marly subsoils and the Chlorosis or Yellowing of Citrus Trees. Calif. Agr. Exp. Sta.'Cir. Xo. 27 (190(5). BULLETIN 318 THE EFFECTS OF ALKALI ON CITRUS TREES 309 trees reach their usual size on soil that contains injurious amounts of alkali. It has been found that orange trees affected by alkali are unusually susceptible to injury from adverse climatic conditions. Hot winds burn the- young leaves and frosts produce more serious injury than with normal trees. Alkali injury is also accentuated by the lack of care, such as improper tillage, the insufficient use of manure or other fertilizers, and withholding irrigation, thereby allowing the soil to become too dry. If the soil by allowed to dry out excessively, the concentration of alkali in the soil moisture may become harmful, while a more abundant supply of water would so dilute the salts present as to reduce the concentration to a point where normal growth could take place. THE EFFECTS OF IRRIGATION WATER Despite the wide publicity that has been given the subject of irrigation waters and the many analyses that were published by Hilgard in the reports of the California Station, our studies in the different citrus districts suggested the desirability of making a survey of the irrigation water in use at present. More than a thousand samples have been analyzed. It lias been found that the vast majority are practically free from alkali. Especially is this true of the water that is drawn from points located near the large watersheds, such, for example, as the Sierra Nevada and the San Bernardino mountains. Usually the wells that are located near the course of streams that originate in those mountains are also sufficiently pure. On the other hand, wells located at some distance from the large watersheds and relatively large streams that themselves originate directly in the mountains, show a wide range in composition. A con- siderable number of such wells contain notable amounts of salts. These are widely distributed over a considerable number of citrus dis- tricts in several counties. In certain localities the dissolved salts are predominantly chlorides, others sulfates and in still others bicarbon- ates. A few wells have been found to contain large amounts of nitrates. The results of this survey are, on the whole, in close agreement with the published conclusion of Dr. Ililgard. We ([note from him as follows : r> "The investigations made by the Station have shown that aside from the frequently saline character of the well and even the artesian Calif. Ajjr. Exp. Sta. Bull. 128 (l!00), p. :il. 310 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION waters of the petroleum bearing regions of the State in the coast ranges, the streams of that region, especially the smaller ones, are sometimes too strongly charged with alkali (in this case largely the sulfates of soda and magnesia) to be suitable either for irrigation or domestic use. Towards the end of the dry season, even the larger streams of the southern coast ranges, with their diminished flow, some- times show an excess of salts. This seems also to be true of the San Jacinto river, which feeds Elsinore Lake." On the other hand, he says: "The waters flowing from the Sierra Madre, south of the Tehachapi range, are throughout of excellent quality for irrigation purposes, as are all those flowing from the Sierra Nevada. The same is true of the artesian waters of the valley of southern California, from Los Angeles east to Redlands. " A considerable number of groves that have been irrigated with saline water have been under close observation for one or more years. As a means of securing information on the effects, soil samples, drawn with a one-inch soil tube, have been analyzed and wherever possible adjacent areas that have been irrigated with comparatively pure water, or virgin soil, have also been sampled. Some of the results are submitted below, together with analyses of the irrigation waters that have been applied. The analytical results are expressed as parts per million of the soil or water. In contrast to previous publications, we have not attempted to estimate the amounts of the several salts present. The state of present knowledge does not make it possible to determine definitely the actual amounts of the different salts that occur in com- plex mixtures, such as irrigation waters or soils. By analysis the components of the different salts may be determined, but while vari- ous schemes have been employed for calculating the amounts of salts present, all of them are more or less arbitrary and have little justi- fication in modern chemistry. Accordingly, the analytical data are submitted as determined without calculating the theoretical salt com- binations. The analyses recorded in table 1 have been chosen to show the wide range in composition found among the irrigation supplies. Some of these contain large amounts of salts, others lesser amounts. As will be pointed out more fully below, the effects of some of these waters have been extremely injurious. Sample Xo. 84 represents suit- able water. This sample, drawn from wells located near the San Bernardino Mountains, fairly represents the main supplies of moun- tain water of southern California, the effects of which have been entirely satisfactory. BULLETIN 318 THE EFFECTS OF ALKALI ON CITRI'S TREES 311 It is not necessary to discuss the amounts of, and variations among, the individual constituents of these waters. Casual observation of the analyses will suffice to show that there is a wide range of difference in the content of total dissolved materials and that a number of the individual constituents occur in certain samples in relatively large amounts. The most significant differences in these waters probably lie in the chlorine and sodium. The unusually high nitrate content of sample No. 119 is a matter of special interest. Where such water is used for irrigation, it is highly improbable that nitrogenous ferti- lizers will be needed. The variations found among samples that contain relatively large amounts of salts, such, for example, as Nos. 642 and 643, are probably of little practical significance. On the other hand, samples Nos. 103 and 105 contain still greater amounts of salts, especially so in the case of the latter. Sample No. 150 is of intermediate composition and represents a type of water that is being used at present on several thousand acres of citrus in California. As will be pointed out later, the use of this water on a lemon grove for a period of approximately twenty years, produced definite injury. The numbers of pounds of a given constituent that will be added to the soil by an irrigation water may be readily calculated from the analysis. For example : an acre foot of water, No. 119, which contains 1479 parts per million soluble solids, will supply the soil 3993 pounds of solids, while an acre foot of No. 84, containing 222 parts per million, will add only 599 pounds. In view of the fact that the amounts of water applied varies widely in different localities and in different years in a given grove, it is not possible to state the exact amounts of salts that have been added to the soil in a given case. It is only possible at present to make qualitative comparisons among the groves. It is evident, however, that large amounts of alkali must necessarily have been added to the soil where such water as Nos. 119, 642 and 643 have been applied. Still greater amounts must have been added in a given period with Nos. 103 and 105, while with No. 150, the rate of salt addition has been considerably less. During the past eight years, several hundred acres of orange orchards located near Riverside, which were previously irrigated with suitable water, have been irrigated with saline water similar to samples Nos. 119, 642 and 643. Other groves adjacent 1o these have been irrigated from the beginning W i1h comparatively pure water (No. !4). So far as can now be determined, the soil in this immediate locality was reasonably uniform and free from alkali previous to planting the orchards. The soil is of a sandy loam character, reason- 312 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION ably deep and free from hardpan. Throughout this district, the soil is deficient in organic matter and nitrogen, the liberal application of both of which is required for successful citrus culture. The orange trees are about twenty-four years old. A number of these groves have been under close observation for a period of about three years. A large portion of the trees irrigated with the saline water have already been severely injured ; some of them are almost dead and a large portion unprofitable. The degree of the injury is much more pronounced at the present time (1919) than it was in 1917, while in 1916 injurious effects had scarcely begun to appear. The accompanying photographs, plates 1 and 2, illustrate the effects and show the appearance of the trees in the spring of 1919. They show the striking contrast between the effects of good irrigation water and water containing alkali salts. In portions of the groves where the saline water has been applied, excessive defoliation has taken place several times. Many of the smaller branches have died and the new foliage has shown excessive mottle leaf. Soil samples from a number of these groves have been analyzed. Some of the results are submitted in tables 2, 3, 4, 5 and 6. The data show that the total soluble salt content of the soil and the amounts of certain individual constituents have been greatly increased as a result of irrigating with saline water. The chlorine and sodium content have been increased to the greatest extent. Other constituents have also been augmented considerably. The data show a direct relationship between the salt content of the soil and the composition of the irrigation water, and the condition of the orange trees is positively correlated with the salt content. It is evident, however, that orange trees are extremely sensitive. The total concentration of soluble matter in a number of the samples was not more than 0.10 per cent (1000 parts per million), even where the trees have been severely injured. The soil samples represent composite mixtures of a considerable number of cores, taken at random from the spaces between the trees where the irrigation waters have been applied. Under the prevailing system of furrow irrigation soluble salts tend to accumulate in greatest amounts between the irrigation furrows and in the unirrigated spaces between the trees, owing to lateral movement. Consequently, higher concentrations probably occur in localized areas between the furrows, than were found in the samples analyzed. While orange trees are more sensitive to alkali than many other crops, it is reasonably certain that with the continued use of these waters the soil will become so heavily charged with alkali as to impair its useful- ness for the more resistant crops. BULLETIN 318 TH E EFFECTS OF ALKALI ON CITRUS TREES 313 The data in tables 4, 5 and 6 show that the salts have evidently penetrated to considerable depths. Samples were taken in three groves to a depth of seven feet, two of which have been irrigated with saline water (No. 643), the other with comparatively pure water (No. 84). Fig. 1. Orange trees irrigated with saline water, No. 643. Fig. 2. Ora >. 84. The analyses establish the fact that Ihe salts have penetrated deeply. The data, suggest that the penetration has even reached deeper than seven feet, bill samples have not been drawn from greater depths. The analyses of samples from the different groves that have been irrigated wilh pure water indicate (hat the original soil must have varied considerably. The variations are not surprising, however, since 314 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION the different groves from which these samples were taken are located considerable distances apart. It may be mentioned in passing, that more or less mottle leaf occurs in many of the groves in this locality that have been irrigated with comparatively pure water. In such cases, the cause of the mottle leaf inheres in the soil itself. Consider- ably more mottle leaf occurs in grove E than in groves M or S. It is interesting to note that the soil of the former differs considerably from that of the two latter. Further discussion on this point will be submitted elsewhere. In addition, the vertical distribution of salts varies in different groves under the same saline irrigation supply. (Compare the data from groves and C, tables 4 and 6.) It is not possible at present to explain these variations. Differences in the amounts of water applied, in cultural operations and in the degree of compactness of the subsoil, are probably among the most important factors. While large portions of these groves have been severely injured, it is interesting to note that the effects have not been uniform over the entire area that has been irrigated with saline water. In some places, little or no effects were evident in 1918, and again in 1919 the degree of injury was still much less pronounced in certain places than in others. It is important, however, that some of the trees which were healthy in 1917 have since begun to show definite signs of injury. Soil samples have been drawn from among the severely injured trees of the grove (B) and from an area of the same grove where the trees have been only slightly injured. Analyses of these samples are submitted in table 7. The results show that the subsoil below the second foot of the severely injured area contains considerably more salts than in the less injured portion. Especially is this true of the chlorine and sodium, the two constituents that seem to be most responsible for the injury in these groves. These variations are probably due to inherent differ- ences in the physical nature of the subsoil which are such as to modify the rates of penetration and accumulation of salts. At any rate, it is interesting that the more severe injury has taken place where the greater amounts of salts have accumulated. As already pointed out, the least affected portions of this grove have now begun to show definite injury. Tt is highly probable that the injury will become severe over the entire orchard if the use of the present irrigation supply be not discontinued. As bearing further on the variability of Ihe effects of saline irriga- tion water, studies have been made on the chemical reactions that take place when salts are added to soils. It has been found that alkali salts BULLETIN 318 THE EFFEC TS OP ALKALI ox CITRUS TREES 315 have the power of reacting with heavy types of soils to a greater degree than with sandy soils. The reactions result in removing limited amounts of sodium from solution and bringing into solution corre- sponding amounts of other bases, composed mainly of calcium. The physical arrangement of the soil particles also undergoes alteration. In view of the fact that soils are extremely variable,, it is not surpris- ing, that the effects of irrigation have not been uniform over a given grove. Analyses of two irrigation waters from Tulare County are also reported in table 1 (Nos. 103 and 105). They contain unusually large amounts of salts. Information at hand does not made it possible to state the exact length of time these waters have been applied. The wells from which the samples were drawn were deepened about four years previously and there is some evidence that water of a radically different character was obtained as compared with that originally supplied. It is probable that one of these wells (No. 103) supplied fairly pure water previous to being deepened. The orange trees to which these waters have been applied are approximately twelve years old and have shown severe injury during the past two years. Soil samples were drawn from these groves and also from adjacent unirrigated fields apparently similar in every way to the soils in the groves. One of these has been used for grain for a number of years, the other still remains in its native state. The soil of one of these groves (T) is of a sandy loam character most of which is underlaid with a dense hardpaii at a depth of from two to three feet. The other is located on the heavy type of soil, belonging to the Porterville clay loam adobe series, locally known as "dry bog." The analyses are reported in tables 8 and 9. The data confirm the results obtained in the study of the groves located near Kiverside. By comparing the irrigated with the unirri- gated soils, it is seen at once that the irrigation has greatly increased the amounts of soluble salts in the soil. While the concentration of practically every constituent has been increased, the chlorine and sodium have been increased to the greatest extent. Comparison of the soil analyses with those of the irrigation waters shows that those con- stituents present in the water in greatest amounts have accumulated in the soil to the greatest extent. The rates of increase, however, are not proportional to the composition of the irrigation water, owiiiir in part, at least, to the fact that citrus trees absorb large amounts of certain constituents, and only small amounts of others. As will be shown elsewhere, eitrus trees do not absorb sodium salts to any -7<5. * The River Irrigating Waters of Arizona Their Character and Effects. Ariz. Agr. Exp. Sta. Bull. 44, 1902. BULLETIN 318 TH E EFFECTS OF ALKALI ox CITRUS TREES 325 Chlorides are undoubtedly the most injurious constituents that occur in the irrigation waters of southern California, but it must not be concluded that other alkali salts can be ignored. In certain locali- ties some of the waters also contain injurious amounts of sulfates and carbonates. Hilgard says, "Unfortunately it is not easy to give abso- lute rules in regard to the exact figures that constitute an excess of salts for irrigation purposes, since not only the composition of the salts, but the nature of the land to be irrigated, and the frequency of irriga- tion required, must be taken into consideration." He concluded that 40 grains per gallon (684 parts per million) is the maximum amount of the total mineral matter a water can safely contain, unless the mineral constituents be composed largely of gypsum. But he also said: "When a large proportion of the solids consists of carbonate of soda or common salt, even a smaller proportion of salts than 40 grains might preclude its regular use." We regret to state that a consider- able number of irrigation waters contain salts in excess of this limit, some of them greatly so. It has also been shown that the continued application of nitrate of soda may bring about an increase in the amounts of alkali in the soil. It is true, the amount of nitrate that has been applied to the experimental plot we have studied is excessive and the results might have been different on other soil or even on the same soil, had it been treated differently in other respects. If nitrate of soda be applied in moderate quantities to a porous soil, especially where the rainfall is heavy, or if used in conjunction witli manure and cover crops, it is highly probable that the sodium will be leached more deeply than it has been on the experimental plot at Riverside. However, it is especially important for farmers to understand clearly that citrus trees, as well as many other crops, do not absorb more than very limited amounts of sodium, and that wherever nitrate of soda be applied, either in combination with other fertilizer con- stituents or alone, the sodium will, for the most part, be rejected by the crop and left in the soil. This sodium remains mostly in soluble form and contributes directly to the alkali content of the soil. All sodium salts are really alkali salts. As has been repeatedly stated, small amounts of none of them art' injurious, and in the case of the nitrate, limited amounts undoubtedly stimulate the growth of practically all crops; but unless drainage effectively leach the salts from the soil, the continued application of sodium nitrate, or of saline irrigation water, will ultimately produce a harmful concentration of alkali in anv soil. 326 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION It is also a matter of practical importance, that the repeated appli- cation of any sodium salt to soils, followed by leaching with irrigation water, or rains, tends to reduce the porosity of the soil and thereby restricts the movement of the water through it. Sodium carbonate and sodium bicarbonate probably produce this effect to a greater extent than the other common sodium salts, but all of them produce this effect to an undesirable extent. The experimental plot to which nitrate of soda has been applied, has become badly puddled, and the poor physical condition of the subsoil in a number of the groves where saline waters have been applied, form one of their striking character- istics. The surface soil in some of these groves has become exceedingly baked, so much so as to be readily detectable by merely walking over it. Hence, the effects of alkali are not wholly determined by the con- centration of salts in the soil. The adverse physical conditions must also be considered. Therefore, wherever nitrate of soda or saline irrigation water be used in regions of light rainfall, especially if applied for any con- siderable length of time, it is important for farmers to understand that the soil must be kept open and porous. This can probably best be accomplished by growing deep-rooted cover crops and plowing under organic materials, such as manure or bean straw. While ordinary irrigation and rains tend to leach more or less alkali down below the reach of citrus roots and probably accomplish this end quite effectively in some soils, our investigations show that the application of saline water has resulted in material!}' increasing the amounts of alkali within reaeli of the roots of the citrus trees. The soil types and climatic conditions of these groves vary widely. Some of them, not reported above, occur in the districts of comparatively heavy rainfall and on soils ordinarily considered to be naturally well drained. As suggested above, the irrigation supplies rarely contain enough alkali to harm citrus trees directly. So far as we have been able to learn, no detrimental effects occurred in any of the groves until after the saline waters had been applied for a period of years. The injury came about rather through the concentration resulting from the accumulated residue, left by the evaporation of repeated applications of water, as was pointed out by Dr. llilgard many years ago. An excess of chlorides causes the tips and margins of citrus leaves to become yellow or brown, followed by defoliation. Sometimes a large portion of the leaves fall and the young, tender shoots may be killed. An excess of sulfates and bicarbonates, on the other hand, is more likelv to stunt the growth of the trees and cause the leaves to become BULLETIN 318 TIIK AFFECTS OF ALKALI ox CITKCS TREES 327 chlorotic. More or less mottle leaf may also occur. Lemon trees are apparently injured by lesser amounts of alkali than oranges. On the whole, the observations and conclusions of Ililgard and Loughridge have been strikingly confirmed. It has again been shown that citrus trees are quite sensitive to alkali and especially to sodium chloride. It is a matter of practical importance for citrus growers to recognize this fact, for sodium chloride is the one constituent most commonly found in irrigation waters that are drawn from wells in the citrus sections of California. As for the treatment of the injured groves, nothing more than the most general suggestion can be offered at present. Where saline irri- gation water is being applied, the first consideration should be to secure an adequate supply of pure water. In fact, so long as the application of saline water be continued, it will be difficult to over- come the harmful effects by any method that may be devised. As suggested by Forbes" an occasional flooding may improve the conditions, by leaching the salts below the reach of the roots, but before flooding be undertaken, the irrigator should assure himself that the subsoil is of such character as will permit deep penetration of the water and allow it to drain away. Otherwise, his efforts will be wasted. After the salts have been washed down below, the soil should be thoroughly cultivated in order to reduce evaporation and thereby check the rise of salts. Where saline water is the only irrigation supply that can possibly be obtained, it may be found desirable, in some cases at least, to dis- continue the furrow system of irrigation entirely and adopt some form of basin or flooding irrigation instead. By that means, the tendency will be to leach the salts down into the subsoil and possibly below the reach of citrus roots. The success of such a scheme will depend largely on the nature of the subsoil drainage and the thoroughness with which it is executed. In addition, the leaching effects of the winter rains should be taken advantage of to the greatest extent possible. As a means to this end, the soil should be put into such condition previous to the rainy season, as will prevent surface run-off and enable the rain water to penetrate deeply. It should be borne in mind, however, that alkali salts are being driven down into the subsoil and that there is a constant danger of the salts rising up around the roots. Furthermore, the continued addition of such large amounts of salts as occur in some of the irriga- tion waters, will materiallv increase the salt content of the natural Ariz. \gr. Kxj>. Sta. Bull. 44 (1!02\ pp. 1<>7 170. 328 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION drainage water. In localities where the volume of the drainage water resulting from such leaching constitutes any considerable portion of the natural drainage water, the ground water may ultimately become heavily charged with salts as a result. This is especially to be feared where the ground water is rising or is already near the surface. In view of these facts, the application of saline irrigation water should be avoided, whenever possible. The experience of the growers near Corona, following the use of water from Lake Elsinore, is of special interest at this time. Some of the groves that were severely injured then, have since recovered and have borne profitable crops of fruit, while others have not yet fully recovered. In general, the most effective treatment was found to consist of thorough tillage, plowing down manure and the applica- tion of suitable irrigation water. If good water be applied freely it is probable that the harmful concentrations of salts that have accumulated will be gradually leached dow r n below the reach of the roots and the use of manure, coupled with deep plowing, will gradually restore conditions favorable to growth. As a means of further increasing the porosity of the soil, an applica- tion of gypsum may also be desirable. In addition to its flocculating effect, gypsum, and other calcium salts also, seem to ameliorate the effects of toxic concentrations of alkali salts, and enable crops to tolerate concentrations of alkali salts that are prohibitive of normal growth in the absence of an abundance of calcium salts. "While somewhat apart from this investigation, it may be appro- priate to state, that a limited study of the amounts of water available to the citrus groves of California leads us to believe that the most promising source from which a supply of really good water can be secured in quantities sufficient to meet the demands of the constantly expanding citrus industry, can be obtained only through concerted effort directed towards the control of flood waters. By the use of suitable check dams, reservoirs, reforestation, and such other devices as will permit the storage of the mountain waters, either above ground or within the water-bearing gravels, an adequate supply of suitable water can probably be obtained. At any rate, the excellent water that falls in the mountains of California, may be so conserved as to augment materially the volume of water now being obtained from them, and thereby make it possible to discontinue the use of at least a portion of the saline water. 10 i" Acknowledgment is due Mr. A. B. Cummins and Mr. S. M. Brown for analytical assistance rendered in connection with this investigation. BULLETIN 318 THE EFFECTS OF ALKALI ON CITRUS TREES 329 t ic oj co o o r 7-1 i I 6*1 71 'CD 7^ M O5 - i i co O ~3" c^ O C i-^ -^ c; ic ru * CO 71 t (J iClCCOCDC-l^rH Ifi CO "5 "^ "ts co co co co ; <- t^ CD ^r CO rC T ~~* fe w CO ,Os 5J r- CJ u o u C ,Os CO O p, g ^r K, C K w ^ K "S^~. ^"~ "~~ O O 1? .c co o c, x -c ^ h- p BO a 00 00 CO 1^ S C*l C 1 -) CO C^ QQ o oc p ic (22- H rfi o Ci g 74 71 CO CO - -r co co ic S o co cr; x *r a v O 00 00 CO i, ^j ^.i DIVISION OF SNu' . HORTICULIU^I- COLLEGE OF AGRICULTURE f~\l Oil 330 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION :TED BY IRRIGATION WATER _0 's 3" oooot o I-H o T-H ^X CM CM CO O g 3 CO * CM Gi T-H CO CO h- cj ttx T ~* 1 ~* *""* ^^ CM T 1 i-H "o PH S 3 io r^ T-H I-H r>. o "^ i ' C^; ^^(MC^ CN CN i-H T-l d^ <^ g_ r-. 1 - GO tM 00 GO T-H CO CM >O ^JO co 10 -^ >o o i>- >c co u^ -2 ^" o ^*" S-^r o ^ C.O o ^CNCO^ (O GO O CO GO CO Tt^ CO CO "^f (H -g-7? ^-00 >-^ tH co E O ft re O r^> cirtr^co O H ^^ -^ S^ C5 & < 7- ^ X rt ^ ^ ro ^ Cj GQ : ^ ft ^5 < 5 ^ ft ^ H 03 _C ^~, ^ '"s H ,S = 1 - C -3 t^ O ^ ^O GO O-l t^- r-^ <^1 T^ 1 ' 1-H S5 co * * CO * rt< CO CO t TCC'StNfNCOtM CO lO O C c m "S "3S t^. CO >O CO CO fa to CO sSs -v Ul "KJ m o 2 'C .^ H ^ , CO ft >i ~ 5 '- 'C H X o ^^ ^^ w X V- O r^ "S^^ c/^ H '"' ^^ K P h ^8 00000^0 ; coco H cT |o O GO CO CO 00 >O O O IO C5 O CO O O H S Sr-!trx -^ r^ <* " ^ /. ^: y. - i r -*-- ^. 5 CC ~ V; -/ . -i: ^ ? i ^M O t'-- ^ '^ =: : -O ^ &,&"&&'"' 1 ~ < ^ o P & CO u 332 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION CO^fOiC rHiCCOCO g?; ^H^nt^^H OOGOOO 1* IO 00 O l~- CN CN * O3 CO CN ri DEGREES OF INJURY TO ORANGE TREES S 3 -^OOOCO rHCOOOO I-H T-H CO CN CN T-H "o Pi s 2^ Tt*CNCOCN ^CO'NCD 1-Hr-HCNCO CNr-HCNr-l at a A H_ I? CDOOO OOOOCO O cDCOOOOi iC^CO^ as ^~^ O o jS'? "e "8 PH S *" D BY IRRIGATION WATER '5' Phosphate Calcium Magnesium Potassium Si (POO (Ca) (Mg) (K) CD CO Ci t- T-H <-H !>* ^ 1C GO I-H I 1 1 I Tf CD 1C 1C CD CN CN CN O CO 1 ^ Qf^ t *- C * o **5 CN -^ > CO CN 4? *< 1 T T I M O> l-H CC 71 EH a (-1 * a^ ^ P^ H 'a S c ^ ABLE 7 o DIFFERK (H V a 03 - D. --'S So 135 ^O ' O^ ^ CD CO ^^ t~~- ^N GO ^* ~* CQ H ^ N ^00 30 ^ ^ W i. ? * J CO cq < < CO 1 |<5 fx * 1> c3 o CN H J c^2 S 2 71 CO H f Q W H rJ a c o T O P O r^ o r cc CO 6 U O^HCOO oorooc ~'-n TJH o> 10 ^f GO GO o co J.l co GO co <-i CO "^ t** CD CO CO a P X 3-S "C p ;c >c p >c o o || CO t^ O CD co M M x - CO CN 1C CO I-H 1 1 CO -^ xCC-^ xCu-^ G -u "3 -* ~ ~y. = c 1-1 CM I-H CN CO BULLETIN 318 THE EFFECTS OF ALKALI ON CITRUS TREES 333 ~ co C-- t^ *-f as co -cX co co 10 IS 1 BJ ^ K H W fi H .0 ff < -iW OJ UJ j, o o 6 H H ^ "c.6 "^^^^diM'-ioj ^2 "o-o ~ * w o r^ ^ r- ^"^ C ^_^ ^ M _fl ^^ -2* _' K .2-S 2 v. a 2^fc >~ o S {; 5 oS'^ ^ ^ "a ^ c P "3 *S % B *> b g S b b Xtn-w'S'~o XtH-^'S-OO' Jt-o^oo-HO 'c.i?^22s b < -2 H d = S c cs 2 ?; C5 fc o o O O y c^ a '5n co i-H r^ O O O O "t< p -^fCMC^CO OOC^CO O-^ T I I ( I I I I 2" ^^^"^ ^ j^? ^ 2 f~ ^ Pn OO'OO CO X "c.O K 10 'f c^J cs ^ x c-: co co H O oe o | i * OS ~l -. ; t^ > I t- i < >H '"e' Ox_- V ' % ' a '5' _= ^^ n _o &H h O _o - a s "S u g ._. h ~ o 's o H fa so SO ^S Ot^t^O -^ '^ rf< C5 C: ss ' & ^ "~ CM ^ -i < |H y> !Q 2 I (N 00 s t-- (N CO 02 S ti 2 s c C3 ^ CH ^> k ^ C* ^ - 03 KH > "*^ < r~ ^ r " -2^? ^> ^ H ^ r . ^ o "^ !- *"* " s ^X) ^"' O^ - - i ^ "^H T~H *-C M ~3" ,- o CO " " t>w '/^ (y ^ y^ "vi 5 t>- t^~ '^t < ^O f^-j OC "^ *^ "^ S C^ CO [s* - I - ^t* fa o 03 O -- ^, ^ ^^H^H^H^H c/} fa 1 OJ 71 03 *r** -^ c ^_ c C; J-* X 0) VI ~ ft - ri ' ^ ^""' *^^ H 1^1 - JH |S ^ S J] Sj ^ -T - 3 * ^j !5 C e 6 o :; S C3> gS g ^^H^rt J> "^^rt H oa - 1-1 "' "3 :- V. ^ p o H S C 6 c5 CO ^ U o 0) H O B ffm ^ j /^^ 1^ 'yQ /-^ ^ ^T T~ o o i 7. l : K) ^^. ic -t -f ro cc cc o o'j j -f ^ v GO 2 U P O 7. j o O} gT O O O b- ~ ^ -^ t s! - - T _ I 71 "* r- 1 -7.^ CB S I> CO If} .- i- 1.1 US -'COO _ J o i- M - i ~ 00 >.o -f ?i co -M i^ i^ ^5 -7 ~J 00 ~i 00 7. " / - S ^ 1 "H -f ^ "= "e = O O CO OO oZ HHOO'^COO'O O i-H OO O t-~ t-- CM CM CO CO 00 OO -* CO 00 t>- GO O5 o 3 M as O300CO>O^r rHCNrHrHOii-H a 03 E <3 S H X S O HH CO !O CO CO !** t^- CM CO n-J rH rH rH CM CM CM *< a &3 % .2 1 H 08 o K ^ IS ofe CMCM":":: 00>o"::": : "S CMcM:::: I-HI-H::::^ (H O 1 a I 5 S t^- 'S 1 ooccMcooooi o & I S " GO rH ^rHOOCOlOrHl-H IO J n S a o fl o 1 8 H .55 CJ ^ $ d 1 O ki >SO E~i 3S2. CB OCMCOO5O5Tti w CO t ^ CO CD O3 fl OlOCOCMTflrH CO 5 * c^ C T^OOO^t H '*O t^^'H^OlCOOO'-l c" 1 ^ t>- rH Tt* Tf^ 'H^ IO t^* CO Tt* CM rH O- ^ z C3 W COcOcOCMOlCM CMCMCMCMcMrH^ p H S O O a: o 6 "ES- 00 GO d "^f C^ I s * O O O O i* I s ** -|y. ^rH^Hr- 4T-H C^^fCOCOC^' 1 ., o CO j o n O u> ^o CJO a O QO . - .- . rH O CM O Ci S -3 rH rH ^ O BULLETIN 318 THE EFFECTS OF ALKALI ON CITRUS TREES 337 _ i-Hi-.OOO.-HCO 10 1^ CO C^ -T "0 Z O *O CO *O *O *O CO **1* *O CO O 1^- OCOfCO^fC^ 10 O G OO "O CO o co >o o-i o X .HO Tf ca 01 co 'f co 2 a^ M - C *< 2 w 'c .S~ X .2 CH H r2 C cj 83Q lr^ o o O O O 2 a -! w w b QJ - ^ *o 1 1 ft, X O S"T" o S *^ tl fH 't QO oo oo ^" GO -2 gg ^H ^ CO CO CD O Q^ c o * o 10 o Ci (N I-H !M t^- Ci H g^ -'' '" H *"" P S H H CO - O ?r^ r r^- t-- t^- >o o t^ 1^ 1C Tf r*< lO U ^ii M ci c^i IM co co C^ (M CO * T}< CO u 5 =: O O O 'O O O re co r^- cc c; oc iO M 4 1 O ' CC 1 GO -.*; Or Si: >n".AL HOR11CUL1UKE 09908 ' COILEGE OF AGR ICULTURE Y. CALIFORNIA This book is DUE on the last date stamped below ct KECTC MAY MM 181971 UHJRL 971 2t9tt tymgt. Form L-9-15m-7,'32 of CALIFORNT*