FERTILIZER EXPERIMENTS WITH CITRUS TREES, p. g. By THE LIBRARY OF THE OF LOS UNIVERSITY CALIFORNIA ANGELES UNIVERSITY OP CALIFORNIA PUBLICATIONS FERTILIZER EXPERIMENTS WITH CITRUS TREES BY R. S. VAILE BULLETIN No. 345 JTTNB, 1922 UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1922 DAVID P. BARROWS, President of the University. EXPERIMENT STATION STAFF HEADS OF DIVISIONS THOMAS FORSYTH HUNT, Dean. EDWARD J. WICKSON, Horticulture (Emeritus). , Director of Resident Instruction. CLARENCE M. HARINQ, Veterinary Science, Director Agricultural Experiment Station. B. H. CROCHERON, Director of Agricultural Extension. H. J. WEBBER, Citriculture, Director Citrus Experiment Station. C. B. HUTCHISON, Plant Breeding; Director of the Branch of the College of Agri- culture at Davis. H. E. VAN NORMAN, Dairy Management. WILLIAM A. SETCHELL, Botany. MYER E. JAFFA, Nutrition. RALPH E. SMITH, Plant Pathology. JOHN W. QILMORE, Agronomy. CHARLES F. SHAW, Soil Technology. JOHN W. GREGG, Landscape Gardening and Floriculture. FREDERIC T. BIOLETTI, Viticulture and Fruit Products. WARREN T. CLARKE, Agricultural Extension. ERNEST B. BABCOCK, Genetics. GORDON H. TRUE, Animal Husbandry. WALTER MULFORD, Forestry. JAMES T. BARRETT, Plant Pathology. FRITZ W. WOLL, Animal Nutrition. W. P. KILLEY, Agricultural Chemistry. H. J. QUAYLB, Entomology. ELWOOD MEAD, Rural Institutions. H. 8. REID, Plant Physiology. Lb D. BATCHELOR, Orchard Management. J. C. WHITTEN, Pomology. FRANK ADAMS, Irrigation Investigations. C. L. ROADHOUSE, Dairy Industry. R. L. ADAMS, Farm Management. W. B. HERMS, Entomology and Parasitology. F. L. GRIFFIN, Agricultural Education. JOHN E. DOUGHERTY, Poultry Husbandry. D. R HOAGLAND, Plant Nutrition. G. H. HART, Veterinary Science. L. J. FLETCHER, Agricultural Engineering. EDWIN C. VOORHIES, Assistant to the Dean. CITRUS EXPERIMENT STATION DIVISION OF ORCHARD MANAGEMENT L. D. BATCHELOR R. S. VAILE G. J. SURR * In eodperation with Division of Agricultural Engineering, Bureau of Public Roads, U. 8. Department of Agriculture. FERTILIZER EXPERIMENTS WITH CITRUS TREES 1 BY E. S. VAILE CONTENTS PAGE Foreword 465 Locations 466 Introduction and Review of Literature 467 Limitations of Orchard Field Trials 472 Rubidoux Experiments ... 473 Outline Plan of Experiments ^473 Planting the Orchard *473 Care of the Orchard 475 Irrigation 476 Differential Treatments '. 476 Yields 479 Additional Data 482 Mottle Leaf 484 Discussion . 486 Arlington Heights Experiment 488 Plan of the Experiments 488 Yields 494 Mottle Leaf 496 Discussion 498 Chaffey Experiment 502 Plan of the Experiments 502 Discussion 503 Additional Growers' Trials 506 California Citrus Soils 508 Conclusions ... ..511 The fertilizer experiments herein described are the results of five separate field trials located in four different citrus growing centers. The experiments were planned and executed by various members of the Citrus Experiment Station staff and the respective owners of three of the properties. Paper No. 83, University of California Graduate School of Tropical Agricul- ture and Citrus Experiment Station, Riverside, California. 466 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Special credit should be given Ralph E. Smith and his co-workers, J. "W. Mills and T. Francis Hunt, for the planning and the early operation of the Rubidoux trial. During the subsequent progress of this trial J. H. Norton, J. Eliot Coit, H. J. Webber, and W. M. Mertz were largely responsible for its success. The Arlington trial was planned and put into effect by H. J. Webber, W. P. Kelley, and W. M. Mertz. Special credit for the suc- cess of this trial is also due to the careful supervision of the field work by Gordon Surr. The Ontario, Chula Vista, and Naranjo trials were planned by R. S. Vaile and his co-workers and carried into effect by the respective property owners. Charles J. Booth's cooperation in the Ontario experiments and J. A. Prizer 's attention to the Chula Vista trials were in a great measure responsible for their success. For the past two years R. S. Vaile has been in charge of the first tw"o mentioned experiments and has been associated with the other trials from their beginning. (Signed) L. D. BATCHELOR, In charge, Orchard Management Division, Riverside. Experiments on the fertilization of citrus fruit trees are here reported. Navel and Valencia oranges, Eureka and Lisbon lemons, are included in the report. This is intended as a progress report covering the years 1907- 1920 inclusive. LOCATIONS RUBIDOUX The experiment of longest standing is located on the University of California Citrus Experiment Station's property, Rubidoux site, Riverside. The soil is partly Sierra loam and partly Placentia loam. The trees were planted in 1907. Differential fertilizer treatments were installed at once and have been continued to date without interruption. All four varieties of citrus trees mentioned above are included in the experiment. ARLINGTON A second trial is located in an old Navel orange grove in Arlington, planted in 1890 on Placentia loam soil. The trials were conducted from April, 1915, to February, 1920, inclusive. BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 467 ONTARIO A third trial is located on an old Navel orange grove at Ontario, planted on Hanford gravelly loam in 1899. The trials were conducted from September, 1915, to February, 1921, inclusive. CHULA VISTA A fourth trial is located on a young Eureka lemon grove at Chula Vista, planted in 1915 on Kimball sandy soil. The trial was con- ducted from June, 1915, to December, 1920. IMARANJO A fifth trial is located on a Navel grove at Naranjo, planted in 1907 on San Joaquin loam soil. The trial was conducted from March, 1916, to December, 1920,. inclusive. Reference is also made to several other growers' field trials with fertilizers, and to orchard practice surveys. INTRODUCTION AND REVIEW OF LITERATURE The conclusion that citrus groves in southern California must be fertilized if they are to be profitable is supported by surveys made by Experiment Station workers during the past fifteen years and by abundant field evidence that is recognized as valid by all successful growers. On the other hand, there is little definite information concerning either the specific kinds and amounts of fertilizer or the time and method of application, from which the greatest returns may be expected. The general field practice of successful growers might be expected to give valuable information on these points, but there has been so much variation in the use of fertilizers and in cultural practice that it is very difficult to determine what particular operation is respon- sible for success or failure. A field survey conducted during 1907 by Smith, Ramsey, and Babcock 2 records the fertilizer treatment for at least a five-year period on each of 50 groves. These groves were scattered throughout the citrus districts and in each case were well above the average in yield for their locality. On an average, 90 pounds of actual nitrogen was applied per acre annually. The range of application was from 21 2 Unpublished notes, Citrus Experiment Station, 1907. DIVISION OF SUBTROPICAL HORTICULTURE COLLEGE OF AGRICULTURE cv r A IPORNIA 468 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION pounds nitrogen annual!}' to 295 pounds annually for the five-year average. No striking differences in crop yields or quality were shown from this wide range in the use of nitrogen. In 1915 a partial survey of the Ontario-Upland colony was under- taken. The accompanying graph (fig. 1) shows the yields, together with the amount of nitrogen actually applied annually on ten groves for which at least five years' records were available. Yield;- field boxes per acre Nitrogen pounds applied per acre -) 800 Uoo 700 \ 00 ^^ 300 ^00 / N v^ 1|_00 \ \ / i i V v. 200 300 \ ,' \ i \ 200 i \ ,'' N N ion i no ^x f X n s n Grove Ho. 10 Fig. 1. Graph showing relation of yield to quantity of nitrogen applied. Average annual yield for five years (solid line) and average annual application of nitrogen (broken line) on ten groves in Ontario-Upland colony. The heavily fertilized groves show a marked tendency to be heavy producers. Again, however, there is no definite evidence for choice between fertilizer materials. During 1919-1920 a similar survey was conducted in the San Dimas-Covina district. Fifty groves were listed, for which five-year records were available. Of these fifty groves, the nine with the largest nitrogen applications (i.e., 176 to 275 pounds per acre annually) produced an average of 240 field boxes of fruit per acre. The nine groves with the smallest nitrogen applications (i.e., 76 to 100 pounds per acre annually) yielded 255 field boxes per acre annually, indi- cating that in these groves the smaller application of nitrogen had maintained the yields as well as the larger applications had. Other factors may have existed, but the yields were reasonably good with either amount. BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 469 Fertilizer field trials with citrus trees have been reported from Florida, Cuba, Porto Rico, Spain, Italy, and elsewhere. The results of such trials are of only passing interest to California growers because of the wide differences of environment. It may be instructive to note, however, that the Porto Rico trials 3 showed the greatest increase in yield following the use of a complete fertilizer, and that the addi- tion of nitrogen was more effective than the addition of any other of the simple elements. The amount of fertilizer commonly used a few years ago on the orange groves of Spain, when reduced to essential plant foods per acre, has been stated to be as follows : 4 Nitrogen from 75 to 90 pounds per acre. Phosphoric acid (P 2 5 ) from 75 to 90 pounds per acre. Potash (K 2 0) from 30 to 60 pounds per acre. A surprisingly large proportion of the quantity of material that has been published in California on the general question of citrus fertilization is but a reflection of opinion or casual observation rather than the report of experiments. Briggs, Jensen, and McLane 5 in 1916 published the results of a careful field survey covering 130 orange groves and 45 lemon groves in Riverside and San Bernardino counties. They stated that ' ' orchards fertilized with organic substances, such as stable manure or cover crops plowed under, usually show; d less mottling than groves supplied principally with commercial fertilizers. Groves which for some years had received only the 'complete' fertilizers, in general use in the areas studied, were badly mottled in all cases, so far as observed in these studies. This was also the case where sodium nitrate was used alone or as the principal fertilizer for some years. An impartial statistical study of the data from individual orange groves shows that approximately one-half the mottling can be accounted for by the low humus content of the soil. ' ' The same authors 6 in discussing the mulched-basin system of irrigated citrus culture submit that a marked improvement followed the installation of this system on certain test plots under their direc- s C. F. Kingman, Citrus fertilization in Porto Rico. Porto Rico Agr. Exp. Sta., Bull. 18, p. 33, 1915. * De Mendoza, Fertilizing oranges in Spain, Calif. Cultivator, vol. 41, p. 559. s L. J. Briggs, C. A. Jensen, J. W. McLane, Mottle leaf of citrus trees, Jour. Agr. Research, vol. 6, no. 19, pp. 721-739, 1916. 6 The mulehed-basin system of irrigated citrus culture and its bearing on the control of mottle leaf, U. S. D. A., Bull. 499, 31 pp., February, 1917. 470 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION tion. The improvement was evidenced by the increased vigor and yield of the trees, the disappearance of mottle-leaf, the elimination of soil plow-sole, and the increase of humus. McBeth 7 in discussing the relation of soil nitrogen to the nutrition of citrus plants, states that "the furrow system of irrigation fre- quently causes a very unsatisfactory distribution of soil nitrates. In many citrus groves more than two-thirds of the nitric nitrogen in the upper four feet of soil is found in the surface six inches, in which, because of frequent cultivation, few feeding roots are found," and "where the furrow system of irrigation is employed, the fertilizing materials should be plowed down somewhat deeper than the land is cultivated." A large part of the work reported on by McBeth was done on the soils of the fertilizer plots of the University of California at the Rubidoux site, Citrus Experiment Station, Riverside. Young 8 published an article on the effect of fertilizer on the com- position and quality of oranges, based on the results of field trial by the Citrus Experiment Station (other phases of these trials will be discussed in the present publication). In reviewing previous work on the subject, he shows that most of it has been unsatisfactory because it was based too largely on observations of trees where the feeding con- ditions were not completely controlled. Young states in conclusion "that nitrogen is the only fertilizer which in this experiment served to exercise a specific effect on the composition of oranges. Applica- tion of nitrogen to the soil resulted in a slightly lower amount of sugar, a somewhat coarser fruit, and a little less juice in the orange. ' ' These modifications in quality, however, were in no case sufficient to lower the commercial grade of the fruit. Webber 9 has twice presented brief progress reports on the field trials of the University of California at the Rubidoux site, Citrus Experiment Station, Riverside. These reports emphasize particularly three points: 1. Unfertilized trees, under the conditions of the experiment, were not producing satisfactory crops of fruit at six and seven years of age. 7 McBeth, I. J., Relation of the transformation and distribution of soil nitro- gen to the nutrition of citrus plants, Jour. Agr. Research, vol. 9, no. 7, pp. 183- 252, May, 1917. Young, H. I).. Effect of fertilizers on the composition and quality of oranges, Jour. Agr. Research, vol. 8, no. 4, pp. 127-138, January, 1917. Webber, H. J., Fertilizer experiments with citrus fruits, Calif. Cultivator, vol. 41, p. 596, December 11, 1913; The fertilizer requirements of citrus trees, Proceedings of 45th Fruit Growers' Convention at Los Angeles, Nov. 10-14, 1914, p. 101, also in Monthly Bulletin, Calif. State Com. Hort., vol. IV, p. 225, June, 1915. BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 471 2. Nitrogen was the only plant food element that measurably increased crop production at these ages. 3. Mottle leaf had developed by the sixth year to a rather alarming extent on four out of five plots receiving applications of nitrate of soda, but not so noticeably on plots receiving nitrogen from dried blood or stable manure. Vaile 10 gave a progress report on the Arlington Grove experiment before the June, 1920, meeting of the California Citrus Institute, emphasizing : 1. Commercial fertilizer with a high percentage of nitrogen stim- ulated the trees to set a good crop of fruit the same spring the fertilizer was applied, but trees so fertilized did not recover from mottle leaf so well as might be desired. 2. The mulched-basin system of culture had a markedly beneficial effect temporarily, as measured both by crops and by general tree vigor; but at the end of five years this had yielded to evidence of injury both in crop and tree appearance from mottling. 3. Stable manure used consistently for five years left the trees in far better condition than after any other type of treatment, although the beneficial response was neither so rapid nor so pronounced as that whieb. followed the two treatments mentioned above. Mertz 11 has reported the results in certain of the University of California plots at the Rubidoux site, Citrus Experiment Station, Riverside, which indicate a striking increase in citrus yields due to green manuring. 10 Vaile, R. S., Progress Report on Arlington Grove Experiment, California Citrograph, vol. 6, p. 44. December, 1920. " Mertz, W. M., The use of green manure crops in southern California. Univ. Calif., Agr. Exp. Sta., Bull. 292, 1918. 472 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION LIMITATIONS OF ORCHARD FIELD TRIALS Batchelor and Rood 12 have pointed out the great effect which inherent variation of trees and soil has on the accuracy of field trials with fruit trees. They conclude that four repetitions of each treat- ment should be used, and that such repetitions should be mathe- matically distributed throughout the experimental area. The majority of orchard field trials have not been arranged to satisfy these require- ments; in fact, the limitations of space and expense will always make it difficult to do so. Particularly is this true when it is desired that the field trial shall answer in detail many questions concerning the exact type of fertilizing material to use, the economic quantity, and the most advantageous time and method of application. Then, too, it is frequently true that in a series of fertilizer treatments some cul- tural operations should be modified in order to give the optimum results from the particular fertilizer applied. It becomes exceedingly difficult, therefore, to determine to what extent any change in yield has been caused by the fertilizer, or by change in cultural treatment. The writer believes that it is often best to limit field trials with orchard crops to comparative tests of complete systems of manage- ment, without attempting too close an analysis of all the individual factors that may be involved. At best it is obviously impossible to work with all soil types, or with large numbers of individual trees. Practical deductions must therefore be drawn cautiously and with due allowance for changing environment. The orchard trials that form the basis for this report are all subject to certain of the limitations just mentioned. There is lack of a sufficient number of mathematically distributed repetitions to offset the variability in soil that is apparent; at times cultural operations have been kept too empirically rigid, as among the different plots, for the best practical results; frequently the attempt has been made to draw fine distinctions between fertilizer treatments that were actually too essentially similar for contrast. But despite these short- comings there are many indications that seem indisputable and that have real significance in any orchard management program. In this report a distinct effort has been made to combine the results of closely similar treatments in order to strengthen the probability of correct deductions. The details of each of the orchard trials will be treated separately, with a general resume at the close of the report. 12 Batchelor, L. P., and Reed, H. 8., Relation of the variability of yields of fruit trees to the accuracy of field trials, Jour, of Agr. Res., vol. 12, p. 245, Febru- nry BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 473 I. RUBIDOUX EXPERIMENTS OUTLINE PLAN OF EXPERIMENTS When the University of California, Citrus Experiment Station was established at Riverside, one of the first experiments undertaken was a test of the effect of various fertilizers on oranges and lemons. These field trials were laid out and planted in April, 1907. In the original plan of the experiment there are 20 plots lettered from A to T inclusive, each one of which is 3 trees wide by 8 trees long and is surrounded on all sides by a guard row. Each plot contains 6 Wash- ington Navel orange trees, 6 Valencia orange trees, 6 Eureka lemon trees, and 6 Lisbon lemon trees, all of which are budded on sweet orange root stocks. The trees are planted 20 feet apart in squares, giving 108 trees to the acre. At the same time, a second series of trees 13 was planted to test the effect of different root stocks, including sweet orange, on citrus varieties. These trials have received different fertilizer and cultural treatment from that of any of the 20 fertilizer plots A to T. And as it has been thought interesting and entirely fair to compare the trees on sweet orange root with those in the ferti- lizer experiment, plots U and V are included in the present summary. Lisbon lemons are not represented in these plots. The trees in the plot growing on hardpan land, enumerated by Bonns and Mertz, have not been included in this report. The accompanying diagram (fig. 2) shows the arrangement of all the trees and plots. PLANTING THE ORCHARD A considerable portion of the land utilized for these field trials had been under cultivation before the planting of the present orchard. At the time the University leased the property the part occupied by plot U was entirely virgin soil, never having been cleared of its native vegetation. Plots A, B, C, D, E, F, G, H, and the western part of plots I, J, K, L, were above the old irrigation ditch. This land had been dry-farmed to barley, wheat, and kafir corn for nine years. By 1905 and 1906 the barley crops had become very poor. Below the old ditch which ran diagonally through the plots K, L, M, I, and J, the land had been irrigated and cropped to melons two years; sweet is For a full description and discussion of these trials see Bonns, W. W., and Mertz, W. M., Experiments with stocks for Citrus, Calif. Agr. Exp. Sta,, Bull. 267, 1916. 474 t'NIVERSITY OF CALIFORNIA EXPERIMENT STATION potatoes, two years, Irish potatoes, two years, and tomatoes, one year. Near the center of Plot M there was a change in the direction of the canal, and at that point a considerable amount of silt and other debris had collected. This debris was removed from the ditch every year and became scattered on the lower half of plot M. Somewhat similar conditions existed on the lower half of plot J. Valencia Navel E D C B A Plot Havel Bone Potash Blood Check Complet Valencia Eureka Lisbon J I H G P Plot Super Potash Sodiur.i nitro- Manure Navel nitrate gen Done Valencia Eureka Lisbon N M L K Plot Hanure Blood Check Nitrogei Bone Havel (i) Super Potash Valencia Eureka Lisbon V T S R Q P Plot Manure Check Blood Potash Complet< Bone Havel covercrop Valencia Eureka Lisbon N Eur. Val. Havel "g- 2. Diagram showing arrangement of plots in Rubidoux fertilizer trials. BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 475 The land just below the fertilizer experiment block was cut by several old gullies, which, at the time of planting the trees, were almost filled. Three of these gullies extended into the fertilizer block. One entered the lower corner of plot 0, one ran into the lower part of plots S and R, and a third ran up through the lemons in plot Q. These gullies were filled by grading in from the land immediately around them. A considerable amount of soil was doubtless removed from the lower part of plot T, the southwest part of plot S, the southwest part of plot R, and the central west part of plot Q. The ground slopes with a fairly steep grade from northwest to southeast. The soil 14 is not entirely uniform, being a light loam at the upper end, and considerably heavier with a dense subsoil at the lower end. Hardpan is to be found at present close to the surface in the lower part of plot T, and a part of plot V has been left out of the records because of hardpan. Nowhere else on the field is it a factor. The trees for the entire orchard, except the Lisbon lemons, were received from the San Dimas Citrus Nurseries and were planted during April and May of 1907. The San Dimas trees were stored four or five days in the lath-house before shipping. Upon arrival, they were held in the shade of some eucalyptus trees and kept moist- ened until all were planted. They were irrigated immediately upon planting, but the water did not penetrate well into the balls. New growth was thus checked somewhat, but a few days later the balls were broken up with a pick and the trees were re-irrigated, after which they made a vigorous development throughout the season. The Lisbon trees were obtained from the Fancher Creek Nursery, Fresno. They were smaller 'than the San Dimas trees and did not make so good a start the first season. CARE OF THE ORCHARD This series of plots was laid out with the idea of testing the effect of various fertilizing elements, and therefore the general care of the orchard has been kept as nearly uniform throughout as possible. The attempt has been made to maintain a good dry mulch between irri- gations through the summer and to keep the moisture conditions as nearly uniform as possible. For two seasons during the early life of the experiment, the irrigation water was run from north to south with each furrow crossing four plots. For the past several years, however, and during the time when the larger amount of fertilizer 14 The soil on this tract has been classified as Sierra loam. It is very similar, agriculturally, to the more common Placentia loam, and doubtless a portion of it should be so classified. The question of soil types for citrua is discussed at some length on page 509 of this publication. 476 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION has been used, the water has been run from west to east and has been taken off as waste water at the lower end of each plot. Storm water has also been prevented from running from one plot to another. During the first five years of the experiment a winter cover crop of barley was grown on all of the 20 original plots. (Plots U and V had leguminous crops during this period.) This barley was plowed under each year in the spring. Since 1912, plots A to T, inclusive. have been clean cultivated throughout the year. Plots U and V have grown a leguminous green manure crop every winter, which has been plowed down in the spring; these plots, like all the others, have always been clean cultivated through the summer. Comparatively little attention has been paid to priming. So far as possible, even in the nm-down parts, the attempt has been made to treat the trees as nearly alike as their comparative vigor would permit. Heavy pruning, as also attempts to renew the vigor of the trees through pruning, has in no case been resorted to. IRRIGATION The irrigation practice has included five or six applications during the season, commencing generally in April or May and extending through October. Plots U and V have received one more, and occa- sionally two more irrigations, in order to bring the cover crop along satisfactorily in the fall and early winter. Four furrows are used to each middle, and approximately one-half of a miner's inch is used for 48 hours in the four furrows. The irrigation runs are not over 200 feet long, and the intervals between irrigations are 28 to 35 days. During the summer of 1920 moisture determinations were care- fully made before and after each irrigation. The moisture content was reduced to the theoretical wilting point in several instances, but on the whole the moisture conditions have been held rather uniform and satisfactory in the entire field. DIFFERENTIAL TREATMENTS These field trials were designed especially to compare the effects on citms tree growth and production, of specific fertilizers. This was somewhat in the nature of pioneer work, for no one element of plant food was then recognized as the principal limiting factor in citrus production. Consequently, one-element, two-element, and three- element fertilizers were all included in the list tested. On each of the plots where nitrogen has been applied, the same total amount has been given irrespective of the source. This is also BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 477 true of the plots upon which phosphoric acid or potassium has been used. Certain plots have been treated with steamed bone only, and such plots have been considered phosphoric-acid plots, with the appli- cation governed accordingly. Some nitrogen has necessarily been carried in this steamed bone, amounting to from 1/4 to y 3 the amount given the nitrogen-treated plots. One of the superphosphate-treated plots has been given dried blood to furnish nitrogen equal in amount to that contained in the bone. Certain plots have been fertilized with stable manure. "While this manure has not been analyzed each year, it has in general carried about the same amount of nitrogen as has been applied to the other nitrogen-treated plots. Wherever nitrate of soda has been used with organic fertilizers to give nitrogen, it has supplied one-half the total nitrogen. The following outline gives the type of material applied to each plot. A. Nitrate of soda, blood, bone, and sulfate of potash. (Com- plete.) 15 B. No fertilizer. C. Dried blood. D. Sulfate of potash. E. Steamed bone. F. Stable manure. G. Nitrate of soda, blood, and bone. H. Nitrate of soda. I. Muriate of potash. 16 J. Superphosphate. K. Steamed bone and sulfate of potash. L. Nitrate of soda, blood, and sulfate of potash. M. No fertilizer. N. Superphosphate and blood to equal nitrogen in bone plots. 17 0. Stable manure and rock phosphate. P. Steamed bone. Q. Nitrate of soda, blood, superphosphate, and sulfate of potash. (Complete.) R. Sulfate of potash. S. Dried blood. T. Unfertilized. is By common usage, a fertilizer containing each of these three elements, nitro- gen, phosphorus, and potassium, is considered a ' ' complete commercial fertilizer. ' ' isSulfato of potash, 1920-1921. " Blood added beginning with 1914. DIVISION OF SUBTROPICAL HORTICULTUT COLLEGE OF AGRICULTURE 1 i ^ UNIVERSITY OP CALIFORNIA EXPERIMENT STATION U. Stable manure, rock phosphate, and leguminous cover crop. (Vicia atropurpurea., Vicia faba, and Melilotus indica have each been used as cover crops during the experiment.) V. Stable manure, rock phosphate, and leguminous cover crop. In this arrangement several of the treatments have been duplicated and a few of them triplicated. Such plots are grouped together in the presentation of the data. In certain cases, where treatments have been closely similar, although not identical, plots have been 'considered duplicates and grouped. The following combinations are thought to be entirely justifiable and will be considered as contrasting groups. Plot* Treatment U and V Cover crop and manure. F and Stable manure. C and S Dried blood. A and Q Complete commercial fertilizer. G and L Nitrogen and one other element. H Nitrate of soda. E, K, P Steamed bone. J Superphosphate. D, I, R Potash only. B, M, T No fertilizer. The distribution of the plots which make up these groups may be seen by referring to figure 2. Fertilization of the trees started in 1907, the year they were planted, with relatively small amounts. These amounts were grad- ually increased until 1914, when they received the quantity still given annually, which is 1.35 pounds actual nitrogen per tree. 2.70 pounds actual phosphoric acid per tree. 1.35 pounds actual potash per tree. This means approximately 25 pounds per tree of 5-10-5 formula fertilizer (home mixed) on the complete fertilizer plots, A and Q. 10 pounds per tree of dried blood on C and S. 9 pounds per tree of nitrate of soda on H. 14 pounds per tree of steamed bone on E, K, P. 2 pounds per tree of sulfate of potash on D, I, R. 13 pounds per tree of superphosphate on J. 10 cubic feet per tree of manure on plots F and 0. 8 cubic feet per tree of manure on plots U and V. BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 479 YIELDS The presentation of yield data in a comprehensive and at the same time a perfectly fair manner is recognized to be difficult. In this case a table (table 1) is given which shows the total yield for each indi- vidual plot and its relative position in the field. In addition, the plot averages are given in pounds per tree per year for each of three periods of three years each (table 2). The plots that are treated alike are then averaged together to give a final comparison (table 3). The graphs have been prepared to illustrate this final comparison (fig. 3). 1312-1314) inc. lilllll 1918 - I.9ZO inc. I/a. 1 a-n t lg.3*S(>789t Key to "Plot numfrers;- 1. U, I/: Man ur n4 eo^ercrop 2. f t O : Manure. 3. C, S :3riet Blood. 4. H : N.trat* of Soda. 5! A, tt: Cowiplett Commerei*). (>. v ' fp - _ L r * L i fh _ L ' E, J^ i J , 2, J 2 3 2 ; /. C*m 6 59 40 115 115 496 403 14 129 183 137 152 3 7 32 77 29 104 330 523 18 127 144 102 91 2 7 13 57 89 152 333 451 38 173 152 89 65 5 11 45 102 82 154 394 484 42 137 136 83 99 18 14 85 133 172 205 495 587 Ave. 143 147 116 105 7 9 47 82 97 146 410 489 Unfertilized Plots 2 146 165 153 178 67 77 98 165 169 249 633 824 6 71 75 138 110 23 26 112 99 172 157 518 468 10 149 122 167 120 6 6 59 40 115 115 496 403 14 129 183 137 152 3 7 32 77 29 104 330 523 18 127 144 102 91 2 7 13 57 89 152 333 451 22 110 128 111 83 21 16 87 121 139 142 468 490 26 141 110 119 86 83 40 136 150 158 174 637 560 30 106 93 107 62 46 14 116 131 151 142 526 442 34 101 86 97 . 76 16 15 112 137 144 175 470 489 38 173 152 89 65 5 11 45 102 82 154 394 484 42 137 136 83 99 18 14 85 133 172 205 495 587 Avo. 126 127 118 102 27 17 81 110 129 161 482 520 MOTTLE LEAF At the end of five years, there existed differences in the appear- ance of the trees, which wore not entirely reflected by the yields, although it seems highly probable that they would have been had the trials been continued for a few more years. Careful estimates were made of the mottling in December, 1916, and December, 1919, the results of which are given in table 8, TABLE 8 Morn.K LEAF, BY GROUPS OK PLOTS Claw I with less than 11% mottled leaves. Good condition. Class II with 11-20% mottled leaves. Blight Iy mottled. Class III with 21-30% mottled leaves. Moderately mottled. Class IV with 31-40% mottled leaves. Badly mottled. Number of plot* from each (lump tliat full into nn-li daxx. Class I V Claim I Claw I I Class III Chem. Fert. 1916 1 4 2 (7 plots) 1919 2 Mulched 1916 1 3 2 (6 plots) 1919 Manured 1916 7 5 1 (13 plots) 1919 6 6 Unfertilized 1916 8 3 (11 plots) 1919 8 2 * 1 BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 497 Fig. 12. Arlington trials. Typical tree in manure group of plots. December, 1919. 498 UNIVERSITY OP CA1JPOBN1A EXPERIMENT STATION DISCUSSION The outstanding points of behavior in this experiment are the fol- lowing : 1. There was a decided response to the application of chemical fertilizers applied in April, 1915, as measured by the crop harvested in March, 1916. No other treatment gave any significant increase the first season. 2. There was a continued increase of crop in response to chemical fertilizers throughout the five years. This was accompanied, however, by an increase in mottling. 3. Immediately following the extremely hot weather of June, 1917, the commercial-fertilizer plots and the mulched plots were the only ones that did not drop practically all of their young fruit. 4. The mulched plots showed striking increases during the second, third, and fourth years of the trials, but by the fifth year they were so leriously affected with mottle leaf that the crop was materially reduced. So pronounced was the final effect and so in keeping is it with growers' experiences elsewhere in southern California, that mulching does not seem a possible method to employ permanently on soils similar to that at Arlington. It may, however, be of much value for two or three years. 5. The manured plots responded very slowly to the spring appli- cations of manure, but at the close of the five years they were yielding as well as any other group and the trees showed more vigor and better color than those of any other group. Estimates made of the 1921 crop, after the experiment had been abandoned (no fertilizer was applied during 1920), indicated that the manured plots would yield about 20 per cent more fniit per tree than the chemical-fertilizer group, and 40 per cent more than the mulched group. 6. Under the conditions of these trials, the increases in crop yield accompanying the different group treatments were obtained at much less cost on the chemical-fertilizer group than on either of the others when the full five-year period is considered. When the 1920 crop alone is considered, the difference in favor of the chemical fertilizer group in comparison with the manured group is much less. The mere cost of the fertilizer and of the other materials when charged to the increase in crop yield on the treated trees compared to the adjacent checks was as follows : Cost of special treatment for each pound of increased yield Total 5 years 1920 Chemical fertilizer group 0.7 cents 0.43 cents Mulched group . _ 1.4 cents 5.00 cents Manure group 1.6 cents 0.63 cents BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 499 Fig. 13. Arlington trials. Typical tree in commercial fertilizer group of plots. December, 1919. UWISION OF SUBTROPICAL HDimCULIU* COLLEGE Of AGRICULTURE BERKELEY, CALIFORNIA 5(K UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Fig. 14. Arlington trials. Typical tree in mulched group of plots. December, 1919. BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 501 7. The use of winter green-manure crops has shown no particular advantage on any of the fertilized plots, no matter what the source of fertilizer. On the manured plots the yields have been distinctly less where cover crops were grown than where the land was given clean culture. It has not been possible to analyze the reasons for the lack of benefit from cover cropping in this case, especially in view of the markedly favorable effect of cover crops indicated by the Rubidoux I to - I Jo /- ommircioj Fertilizer arou.a 2 - Mfl.nu.red Group J.- IhnfirM, zed orou.p A. C\en c...1e4 Z ^ov.r.r^pti Fig. 15. Arlington experiment. Diagram showing effect of cover crop. trials. The growth of the cover crop has consistently been highly successful ; neither the cover crop nor the trees ever showed indication of lack of water ; the land both in clean culture and in cover crop was all plowed at the same time and to the same depth each spring. On the unfertilized plots cover crops had a slightly depressing effect in the second and third years, but during the last two years of the trial they seemed to be of- marked benefit. This benefit was not sufficiently great, however, to make the cover cropped portion of the unfertilized plots commercially successful. The effect of cover crops is shown graphically in figure 15. 502 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION 8. Throughout the period of the trials the fruit of best quality was produced on the plots fertilized with dried blood. Second to this was the fruit produced on the manured plots. In both cases the average quality was high. Apparently applications of phosphoric acid and potash are not essential for the production of high quality fruit, under the conditions of these trials. III. CHAFFEY EXPERIMENT 22 PLAN OF THE EXPERIMENTS Another trial with an old Navel grove was located on the orchard belonging to the Chaffey Union High School at Ontario. This grove was planted in 1899. The soil is Han ford gravelly loam. The trial plots were outlined by the writer in collaboration with C. J. Booth of the Chaffey Union High School and Junior College. Treatments were first begun in 1915. There are approximately six acres included in the experiments. Five fertilizer treatments are applied in plots four trees wide by twenty-eight trees long. The treatments consist of: 1. Stable manure, 6y cubic feet per tree. 23 2. "Complete" fertilizer, 5-9-1 1/ 2 , 14 Ibs. per tree, giving 0.7 Ib. actual nitrogen per tree (2 per cent of nitrogen inorganic, and 3 per cent organic.) 3. Tankage, 8-8, 131,2 Ibs. per tree, 1 Ib. actual nitrogen per tree. 4. Ammonium sulfate, 9 Ibs. per tree, 2 Ibs. actual nitrogen per tree. 5. Cottonseed meal, 15 Ibs. per tree, 1 Ib. actual nitrogen per tree. Crossing these five fertilizer plots, four cultural treatments were installed, as follows : A. Winter green manure. B. Winter green manure and 2y 2 tons ground limestone per acre per year. C. Clean culture all year. D. Mulched with straw. Each of these plots is seven trees long by twenty trees wide, and crosses all the fertilizer plots equally. * For other accounts of this experiment, sec Booth, C. J., Bull. No. 3, Dept. of Agric., Chaffey Union High School, and Booth, California Citrograph, vol. 4, no. 8, p. 205, June, 1919. " The amounts of fertilizer used in these trials were originally based on a unit cost per tree, rather than on the amount of plant food contained. BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 503 When the trials were commenced, the grove was badly run down, having been neglected for some time. No fertilizer had been applied for several years and the trees were, in consequence, considerably yellowed with sparse foliage. Irrigation water had been applied in furrows 600 feet long at intervals of 30 days, with the result that the light soil at the upper end of the grove (sub-plot A) had been leached of much of its plant food, while the trees in sub-plots C and D had evidently suffered from lack of water at times. To remedy these conditions, an auxiliary pipe line was installed at the head of sub- plot C and the irrigation interval was reduced to 14 days. One and a quarter acre-inches of water were applied at each irrigation. In contrast to the Arlington plots, mottle leaf was not a serious problem on this grove at the beginning of the trials. Lack of available plant food seemed to be the principal limiting factor. Sub-plot A was very much poorer in the beginning than ony of the others, and should hardly be compared with the balance of the orchard, even yet. The rest of the grove was uniform. The diagram (fig. 16) shows the arrangement of the plots and the treatments, together with the total six-year yield. The yield per year is shown in table 9. DISCUSSION 1. The striking increase in the 1921 yield over any previous yield is the outstanding point in the experiment. The evidence is very clear that a badly run-down grove can be brought back into heavy bearing only after several years of good care. 2. Analysis of the 1916 and 1917 yields shows that the plot receiv- ing the more readily available nitrogen in the form of sulfate of ammonia responded only slightly more quickly than the one receiving cottonseed meal, but the sulfate of ammonia plot, with 2 pounds of actual nitrogen per tree, did give a considerably better yield in 1917 than the ' ' complete ' ' fertilizer plot, with only .7 pound actual nitro- gen per tree. This indicated that the amount of nitrogen was of more importance for the first year than the kind of fertilizer. 3. On the other hand, the yields in the later years (1920 and 1921) were no greater with the 2 pounds of nitrogen per tree than on the plots given 1 pound or .7 pound of nitrogen. 4. The total six year yields on the five fertilizer plots are certainly within the range of natural variation for such trials. 504 I'NIVKRSITY OP CALIFORNIA EXPERIMENT STATION 5. The mulched plot has consistently shown a marked superiority over any of the other cultural plots. This superiority was in evidence as early as 1917 and was most pronounced in 1919. 6. Mottle leaf commenced to appear on the mulched plots early in 1919. By February, 1921, it was recognized as a serious factor, par- ticularly in sub-plots ID and 2o. As the mottle leaf increased, the superiority of the mulched plot diminished. In 1921 mottle leaf had also developed to some extent throughout the sulfate of ammonia plot, and especially in the clean cultivated portion. 7. The six year average yield on the cover cropped area of all the plots together is identical with the yield on the clean cultivated area. The high value of organic material is, however, strongly indicated in the sulfate of ammonia plot, where the sub-plot in which cover crops have been grown is markedly superior in yield and appearance to the clean cultivated sub-plot. The exact reverse of this condition exists in the "complete" fertilizer plot, one reason for which would seem to be the relatively small applications of nitrogen, which may not have been sufficient for both trees and cover crop during certain critical periods. Sulfate of Cottonoeed ter Plot anure Complete Tankage ammonia meal 1.2 * ), e. 370 me 362 518 35U Sub -plot A cover-crop 1,07 U57 U2 5 U99 531 5 * D covr rcrop lime cnn ft. 502 1^60 U56 589 C Clean Culture 72U 796 710 710 611 D Kulch 70<5 516 523 5U8 Fig. 16. Chaffey Experimental Grove. Diagram showing arrangement of plots and average total yield in pounds per tree for six seasons, 1916-1921, inclu- sive. WYISION OF SU6IROPICAL HORTICULTURE COLLEGE OF AGRICULTURE BERKELEY, CALIFORNIA BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 505 TABLE 9 CHAFFEY GROVE, AVERAGE YIELDS IN POUNDS PER TREE. Six YEAR SUMMARY 1916 1917 1918 1919 1920 1921 Total 6yrs. 1A Manure 00 63 14 91 44 158 370 2A Complete 7 5? 9 94 81 175 418 Covercrop 3A Tankage 9 61 00 80 65 154 362 4A Sul. Am 99 5 100 107 207 518 5A Cottonseed meal 1 58 9? 80 158 419 All A ? 67 1 91 76 170 407 IB Manure... . 4 98 6 103 64 182 457 Covercrop 2B Complete . . 1 54 111 76 183 425 Lime 3B Tankage 1 76 106 73 ?43 499 4B Sul. Am 3 125 103 98 202 531 5B Cottonseed meal 2 126 120 112 ??4 584 A11B 2 96 1 109 85 207 500 1C Manure 13 95 2 101 108 221 540 Clean 2C Complete 16 63 84 131 208 502 Culture 3C Tankage 12 98 35 101 214 460 4C Sul. Am . . 4 138 2 45 65 202 456 5C Cottonseed meal 8 102 80 96 243 589 A11C 10 111 1 69 100 218 507 ID Manure 24 125 76 175 122 202 724 2D Complete . .. 30 94 108 212 123 229 796 Mulched 3D Tankage ?,?, 91 38 174 120 265 710 4D Sul. Am 21 167 41 148 135 198 710 5D Cottonseed meal 12 123 12 110 115 239 611 A11D 22 120 55 162 123 227 709 1. Manure 9 95 18 118 85 191 516 2. Comolete 12 66 18 125 103 199 523 3 Tankage 8 81 i 99 90 219 504 4. Sul. Am 6 132 8 99 101 202 548 5. Cottonseed meal ... 6 117 2 100 101 216 542 DIVISION OF SUBTROPICAL HORTICULTURE COLLEGE'OF AGRICULTURE BERKELEY, CALIFORNIA 506 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION ADDITIONAL GROWERS' TRIALS In 1914 Vaile reported 24 the results of three growers' field trials, located respectively in Yolo silt loam near Santa Paula, Placentia loam, at Riverside, and Hanford gravelly loam soil, at Pomona, two of which showed unmistakable results from the use of nitrogenous fer- tilizers, but were without noticeable results following the use of potash or phosphoric acid. The third trial, designed merely to test the effect of potash, was entirely negative in results. A field trial with the use of nitrogenous fertilizers was conducted by a grower of lemon trees on Yolo gravelly light sandy loam soil near Santa Paula, beginning in 1914 when the trees were seven years old. A vigorous winter cover crop was grown every year, and in addition fairly liberal applications of dried blood, manure, and sulfate of ammonia were used. Two middles, completely surrounding one row of 36 trees, were left without fertilizer of any sort except the cover crop, for five subsequent years, during which time they produced an average of 8.3 field boxes of lemons per tree annually, while the first fertilized row adjoining produced an average of 9.6 field boxes. An orange grove located on Hanford gravelly sandy loam near Pomona, was fertilized with nitrate of soda, superphosphate, and tankage, for the five years of 1911-1915 inclusive. One strip through the grove was supplied with sulfate of potash at the rate of two pounds per tree annually throughout this period. There was no meas- urable difference following the use of potash. In another case on Yolo loam soil near Fillmore, six adjoining plots of lemons were laid out in 1911. Five were fertilized respectively with sodium nitrate, dried blood, ammonium sulfate, tankage, sodium nitrate, and superphosphate, while one was left unfertilized. In 1917, after these treatments had been continued for seven years, the unfertilized trees could be picked out by observation, but the increased yields had hardly paid for the fertilizer applications. There was no measurable difference in tree growth, yield, or fruit quality, between the variously fertilized plots. A growers' cooperative field trial at Chula Vista, with young lemon trees planted in 1915 on Kimball sandy loam soil, was outlined by the writer and conducted from 1915 to 1920 inclusive. Lemon trees had previously grown on this land for at least 20 years, but the young * ProoeeiiinjjH of the 45th California State Fruit Growers' Convention, Los Angeleu, Nov. 10-14, 1914, p. 135. BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 507 trees were not planted in the holes from which the lemon trees were removed. There were five major plots, each comprising four rows of thirty trees, with unfertilized guard rows surrounding each plot. Each of these major plots was crossed by secondary treatments so that the plots were divided into four sub-plots, designated as A, B, C, D. The treatments were as follows : Plot 1 Basined and mulched. Plot 2 Fertilized with complete fertilizer. Plot S Fertilized with sulfate of ammonia. Plot 4 Fertilized with dried blood. Plot 5 Fertilized with stable manure. Sub-plot A. Clean cultivated. Sub-plot B. Winter cover crop. Sub-plot C. Winter cover crop and superphosphate. Sub-plot D. Winter cover crop and ground limestone. At the end of the second year the unfertilized guard rows were easily distinguishable because of lighter colored foliage and shorter growth. At the end of the third year, the basined and mulched trees were distinctly the largest of all on the tract. The trees fertilized with sul- fate of ammonia were second in size and had darker colored foliage than any others. By this time the inferiority of the unfertilized trees was so pronounced that sulfate of ammonia was subsequently applied to all of them. At the end of the fifth year the average total yield from the several plots was as follows : Yield in field Plot boxes per tree Mulched basined _ 5 Sulfate of ammonia 4.5 Dried blood 3.0 Complete 3.0 Manure 2.2 Orchards adjoining on three sides, planted at the same time, but unfertilized the first four years, had yielded practically no fruit to the same date. None of the sub-plots showed any significant differences except that the use of lime seemed to make an increased growth on plots 2, 3, and 4, when compared to the superphosphate sub-plots immediately adjoining. This is the only case in any trial noted where lime seems to have been a factor in increasing growth. A somewhat similar trial planned by the writer was conducted from February, 1916, to date, with Navel oranges planted in 1907 on 508 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION San Joaquin 25 loam soil, near Naranjo, Tulare County. There were four major plots, each divided into four sub-plots as follows : Plot 1 Plot t Plot S Plot 4 Fertilized Fertilized Fertilized Fertilized with nitrate with 8-8 with 4-10-2 with stable of soda. tankage. complete fertilizer. manure. Sub-plot A. Winter cover crop. Sub-plot B. Winter cover crop and lime. Sub-plot C. Clean culture. Sub-plot D. Mulched. There are no outstanding differences between these plots except (1) all of the mulched sub-plots showed a marked increase the first year, but owing to local drainage difficulties and gopher injury, the significance of this treatment was soon lost. How long the increase would have continued is therefore not known. (2) The manured plot seems to show the greatest total improvement to date as manifested by the 1920 crop and the present condition of the trees. All these trials indicate that fertilization with nitrogenous mater- ials has a positive effect on citrus fruit production, but that fertil- ization with phosphoric acid and potash usually does not have any measurable effect. There is little or no real evidence from any of these trials regarding the kind of nitrogenous fertilizer or the amount that may be expected to give the best results. CALIFORNIA CITRUS SOILS The field trials with fertilizer on citrus trees discussed above are located on various types of soil. It has often been said that soil types have a great deal to do with fertilizer practice and its results. With these points in mind the following brief description is appended to the consideration of citrus fertilization. A large part of the material presented is summarized from the reports of the soil surveys con- ducted jointly by the U. S. Bureau of Soils and the College of Agri- culture. The convenience of such a summary for reference seems to justify its publication here. Soils may be variously classified according to their geological formation, the nature of the parent rocks from which they are formed, the degree of coarseness or fineness of their physical make-up, their 25 San Joaquin soil is very similar to Placentia. It is an old alluvial, derived from granitic rocks and underlaid by hardpan at from three to four feet. 'H JOVW. .:;*.? . fr-.'-IVfC - BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 509 chemical composition, their native flora, or their agricultural history and performance. To what extent each of these classifications may be of value to an orchardist is a matter of dispute : certainly any classification, to be of value, needs to be carefully interpreted. Citrus fruits are grown on a wide range of soils in southern Cali- fornia, and yet these soils generally fall into a comparatively few gen- eral groups. If the classification of the Bureau of Soils is used, it is found that not less than 90 per cent of citrus planting in southern California 26 is on soils belonging to the Hanford, Yolo, Ramona or Placentia series. The preponderance is in the order given. Hanford soils are recent alluvials, derived from granitic rocks, light brown in color, moderate to low in organic matter, high in alkali- forming bases (potassium and sodium), never underlain by hardpan but often by coarse gravel. The native vegetation is various, but is predominatingly composed of good to heavy cover of coarse chaparral with sparse foliage. 27 This growth is mainly perennial, with short and sparse grass and other annual development. Occasional oak groves are noted, and sycamores follow the stream courses. Alfilaria and occasionally malva are sometimes rank on newly cleared tracts. Yolo soils are also of recent alluvial origin, but are derived from shales and other sedimentary rocks. They are gray or light brown in color, moderately to well supplied with organic matter, moderate to low in potassium and sodium, never underlain by hardpan but fre- quently by a heavier loam than the surface, and occasionally the sub- soil is very high in lime. Drainage is apt to be poorer than in the Hanford series and therefore alkali accumulations are commonly injurious in the lowlying tracts. The native vegetation is predom- inatingly composed of rank-growing annuals of which the mustards and malvas possibly are most general. Tree growth is largely limited to willows, in the moist locations. Ramona soils, derived from granitic rocks, are of much older alluvial origin. They are light brown to light red in color, low in organic matter, high in potassium and sodium, sometimes underlain 26 Tulare County presents a rather different range of soil types that are used for citrus planting, including two series derived from basic igneous rocks and two series of old alluvial soils derived largely from granitic roeks. 27 This use of the term ' ' chaparral ' ' is possibly open to criticism. As used it is intended to include a number of woody stemmed perennials of which the following list is representative: (1) Adenostoma fasciculatum H. & A. (grease- wood or chamiso) ; (2) Artemesia calif arnica Less. (California sage) ; (3) Ceno- thv divaricatus Nutt. (California lilac) ; (4) Eriogonum fasciculatum Beuth. (wild buckwheat) ; (5) Lotus glabra Greene (deer clover) ; (6) Querous dumosa Nutt. (scrub oak) ; (7) Salvia apiana Jepson (white sage) ; (8) ETiamnus cali- fornica Esch. (wild coffee); (9) Bhus laurina Nutt. (sumac); (10) Prunus ilici- folia Walp. (wild cherry). DIVISION -OF surtiwricAL HORHCULIUKL COLLEGE OF AGRICULTURE BERKELEY, CALIFORNIA 510 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION by a hardpan at 3 to 6 feet. Drainage is generally fair to good. The native chaparral is neither so thick nor so rank as on the Hanford soils, but is of much the same general character. Placentia soils are similar to Ramona, but are redder in color and poorer in organic material. Hardpan is more general and closer to the surface, and when there is no hardpan there is frequently a very compact clay subsoil. Drainage is apt to be poor in spots because of the undulating nature of the hardpan and the clay subsoil. Native vegetation is very sparse. Native tree growth is almost wholly lack- ing on both Ramona and Placentia soils. Generally speaking, all of these soils are potentially alkaline and are moderately to well supplied with mineral plant food elements. In southern California there is almost no citrus planted on residual soils. Contributing reasons for this may be that most of the residual soils in the district are on rather steep hillsides, where irrigation is difficult. It is also true that a high percentage of local residual soils are of heavy texture and that they are usually underlain with bed rock at rather shallow depths. In physical composition the range of citrus soils includes all the grades of loams from gravelly sandy loams to clay loams. The clay loams are limited in extent and are rarely used for citrus except in the Whittier area. Silt loams are common in the Whittier, Orange County, and Ventura County districts. In general, the lighter, coarser loams are much more widely used for citrus than the finer ones. In the Hanford series the coarser loams predominate. The Ramona and Placentia soils are most apt to be medium loams, frequently underlain with clay loam subsoils, while the Yolo soils are more often of the finer texture. The Hanford soils (loam to gravelly loam) are found throughout the foothill district from Pasadena to Highland and extend outward to include practically all the citrus plantings in the Pomona and east- ern San Gabriel valleys. Much of the San Fernando Valley, particu- larly the Mission tract, is typical of Hanford, as is also the land contiguous to the Santa Ana River, from Redlands through to Olive, Anaheim, and Garden Grove. The Yolo soils (loam, silt loam, and fine sandy loam) occupy all the principal citrus areas of Ventura County except the Ojai Valley ; 28 the Corona and the Placentia-Fullerton districts and much of the Santa Ana-Orange-Tustin district are composed of Yolo soils. 28 The citrus orchards of the Ojai are planted on an old alluvial soil derived from shales which have been classified under the Ojai series. BULLETIN 345] FERTILIZER EXPERIMENTS WITH CITRUS TREES 511 In southern California the Ramona soils are found generally in smaller blocks than the Hanford and Yolo series. The main distri- bution includes areas south and east of Los Angeles, the Alhambra district, small areas near Santa Ana, a long narrow strip at San Dimas, a very small area northwest of San Fernando, and a consider- able acreage in the Riverside region. The Plaeentia soils are almost entirely confined to the Arlington- Riverside district and the Redlands district. In general the climate is cooler and the rainfall greater in the districts where the Yolo soils predominate than in those localities where the Hanford and Ramona and Plaeentia soils are more common. As exceptions, Hanford soils are found in the strictly coast area below Anaheim, while Yolo soils are found at Corona and at the upper end of the Little Santa Clara Valley where the hot interior climate prevails. As a consequence of these climatic differences, rather than of the soil differences, the Yolo soils are more generally used for Valen- cias and lemons, while the finest Navel groves are planted on Hanford or occasionally on Ramona soils. CONCLUSIONS Certain points of emphasis are consistently shown by each of these experiments: 1. There is a positive value to be derived from fertilizing citrus trees on any of the soils involved in these trials, as measured by in- creased crop yields. 2. This value seems to be associated primarily with the use of nitrogen. 3. No definite value can be attached to the use of potash or phos- phoric acid in any of the trials reported, either when used in conjunc- tion with nitrogen or when used alone. 4. Lime, applied as ground limestone, has not been of value in the trials reported except at Chula Vista on the Kimball sandy loam soil. 5. Bulky organic material has been of large importance in citrus fertilization. 6. Specific fertilizing materials have given different results in different locations ; so much so that findings from one set of field trials should not be too literally interpreted for any other set of conditions. 512 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION 7. Field trials with fruit trees are generally designed to measure the effect of contrasting systems of orchard management and cannot furnish exact answers to specific questions concerning the economy of any certain kind, amount, or method of application of fertilizer. 8. The field trials and orchard surveys reported upon in this pub- lication indicate clearly that fertilization is required for the economical production of citrus fruits under usual southern California conditions. That the application of fertilizer is often delayed too long after the planting of an orchard, and that larger applications might be used with profit, are points that are also indicated. 9. Groves that have been allowed to deteriorate through lack of fertilizer may be greatly improved by the use of nitrogenous fertilizer materials. Where deterioration is manifested by typical mottle leaf and attendant characteristics, it appears that a correction of this par- ticular trouble is not to be found in the use of commercial fertilizers, particularly inorganic fertilizers. 10. Covering the ground with a straw mulch, thus eliminating the necessity for any tillage operations, may be expected greatly to im- prove run-down citrus groves. This method of culture is likely to be limited in effectiveness to a period of two or three years, following which ordinary tillage should again be resorted to. This system of management is not well adapted to clay loam soils. 11. The use of winter green-manure crops has been followed by conflicting results in the different trials. In one case a marked increase in yield and an improvement in tree condition resulted; in a second case there was a slight decrease in yield ; in a third case the results seemed to be negative. The failure of the cover crop to always produce increased yields can apparently be accounted for in some cases, but has not been in other cases. STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION BULLETINS No. No. 251. Utilization of the Nitrogen and Organic 309. Matter in Septic and Imhoff Tank Sludges. 310. 253. Irrigation and Soil Conditions in the 312. Sierra Nevada Foothills, California. 313. 261. Melaxuma of the Walnut, "Juglans 316. regia." 317. 262. Citrus Diseases of Florida and Cuba Compared with Those of California. 320. 263. Size Grades for Ripe Olives. 321. 267. Experiments with Stocks for Citrus. 323. 268. Growing and Grafting Olive Seedlings. 270. A Comparison of Annual Cropping, Bi- 324. ennial Cropping, and Green Manures on the Yield of Wheat. 325. 273. Preliminary Report on Kearney Vine- yard Experimental Drain. 275. The Cultivation of Belladonna in Cali- 330. fornia. 331. 276. The Pomegranate. 332. 278. Grain Sorghums. 334. 279. Irrigation of Rice in California. 280. Irrigation of Alfalfa in the Sacramento 335. Valley. 282. Trials with California Silage Crops for 336. Dairy Cows. 283. The Olive Insects of California. 337. 285. The Milk Goat in California. 339. 286. Commercial Fertilizers. 287. Vinegar from Waste Fruits. 340. 294. Bean Culture in California. 297. The Almond in California. 341. 298. Seedless Raisin Grapes. 342. 299. The Use of Lumber on California Farms. 343. 304. A Study on the Effects of Freezes on 344. Citrus in California. 308. I. Fumigation with Liquid Hydrocyanic 347. Acid. II. Physical and Chemical Prop- erties of Liquid Hydrocyanic Acid. 348. I. The Carob in California. II. Nutri- tive Value of the Oarob Bean. Plum Pollination. Mariqut Barley. Pruning Young Deciduous Fruit Trees. The Kaki or Oriental Persimmon. Selections of Stocks in Citrus Propa- gation. Control of the Coyote in California. Commercial Production of Grape Syrup. Heavy vs. Light Grain Feeding for Dairy Cows. Storage of Perishable Fruit at Freezing Temperatures. Rice Irrigation Measurements and Ex- periments in Sacramento Valley, 1914-1919. Dehydration of Fruits. Phylloxera-Resistant Stocks. Walnut Culture in California. Preliminary Volume Tables for Second- Growth Redwoods. Cocoanut Meal as a Feed for Dairy Cows and Other Livestock. The Preparation of Nicotine Dust as an Insecticide. Some Factors of Dehydrater Efficiency. The Relative Cost of Making Logs from Small and Large Timber. Control of the Pocket Gopher in Cali- fornia. Studies on Irrigation of Citrus Groves. Hog Feeding Experiments. Cheese Pests and Their Control. Cold Storage as an Aid to the Market- ing of Pluins. The Control of Red Spiders in Decidu- ous Orchards. Pruning Young Olive Trees. CIRCULARS No. No. 70. Observations on the Status of Corn 172. Growing in California. 173. 82. The Common Ground Squirrels of Cali- fornia. 174. 87. Alfalfa. 175. 110. Green Manuring in California. 111. The Use of Lime and Gypsum on Cali- 178. fornia Soils. 179. 113. Correspondence Courses in Agriculture. 115. Grafting Vinifera Vineyards. 181. 126. Spraying for the Grape Leaf Hopper. 127. House Fumigation. 182. 129. The Control of Citrus Insects. 138. The Silo in California Agriculture. 183. 144. Oidium or Powdery Mildtw of the Vine. 184. 148. "Lungworms." 188. 151. Feeding and Management of Hogs. 189. 152. Some Observations on the Bulk Hand- 190. ling of Grain in California. 193. 155. Bovine Tuberculosis. 198. 157. Control of the Pear Scab. 201. 159. Agriculture in the Imperial Valley. 202. 161. Potatoes in California. 164. Small Fruit Culture in California. 203. 165. Fundamentals of Sugar Beet Culture 205. under California Conditions. 206. 166. The County Farm Bureau. . 208. 167. Feeding Stuffs of Minor Importance. 169. The 1918 Grain Crop. 209. 170. Fertilizing California Soils for the 1918 210. Crop. 212. Wheat Culture. The Construction of the Wood-Hoop Silo. Farm Drainage Methods. Progress Report on the Marketing and Distribution of Milk. The Packing of Apples in California. Factors of Importance in Producing Milk of Low Bacterial Count. Control of the California Ground Squirrel. Extending the Area of Irrigated Wheat in California for 1918. Infectious Abortion in Cows. A Flock of Sheep on the Farm. Lambing Sheds. Winter Forage Crops. Agriculture Clubs in California. A Study of Farm Labor in California. Syrup from Sweet Sorghum. Helpful Hints to Hog Raisers. County Organizations for Rural Fire Control. Peat as a Manure Substitute. Blackleg. Jack Cheese. Summary of the Annual Reports of the Farm Advisors of California. The Function of the Farm Bureau. Suggestions to the Settler in California. Salvaging Rain-Damaged Prunes. CIRCULARS Continued No. No. 214. ^"^ Treatment for the Prevention of 236. eal Smuts. 215. r^^inz Dairy Cows in California. 217. Methods for Marketing Vegetables in 237. California. 218. Advanced Registry Testing of Dairy 238. Cows. 239. 219. The Present Status of Alkali. 223. The Pear Thrips. 240. 224. Control of the Brown Apricot Scale and the Italian Pear Scale on Decid- 241. uous Fruit Trees. 225. Propagation of Vines. 242. 227. Plant Diseases and Pest Control. 243. 228. Vineyard Irrigation in Arid Climates. 230. Testing Milk, Cream, and Skim Milk 244. for Butterfat. 245. 231. The Home Vineyard. 246. 232. Harvesting and Handling California Cherries for Eastern Shipment. 247. 233. Artificial Incubation. 248. 24. Winter Injury to Young Walnut Trees during 1921-22. 249. 235. Soil Analysis and Soil and Plant Inter- 252. relation!. . 253. The Common Hawks and Owls of Cali- fornia from the Standpoint of the Rancher. Directions for the Tanning and Dress- ing of Furs. The Apricot in California. Harvesting and Handling Apricots and Plums for Eastern Shipment. Harvesting and Handling Pears for Eastern Shipment. Harvesting and Handling Peaches for Eastern Shipment. Poultry Feeding. Marmalade Juice and Jelly Juice from Citrus Fruits. Central Wire Bracing for Fruit Trees. Vine Pruning Systems. Desirable Qualities of California Bar- ley for Export. Colonization and Rural Development. Some Common Errors in Vine Pruning and Their Remedies. Replacing Missing Vines. Supports, for Vines. Vineyard Plans. (INIVERSJTY of CALIFORNIA LOS ANGELES LIBRARY DIVISION Of SUHiROfWL HORIICULIURE COLLEGE OF AGRICULTURE BERKELEY. tAUFORNW ^Ms book is Df^ on the last date stamnf SB ^69 V19f UC SOUTHERN REGIONAL LIBRARY FACILITY A 001 095 398 2