Bulletin 154 
 
 December, 1919 
 
 UNIVERSITY OF FLORIDA 
 
 Agricultural Experiment Station 
 
 CITRUS FERTILIZER EXPERIMENTS 
 
 By 
 S. E. COLLISON 
 
 The Station Bulletins will be sent free upon application to the Experiment 
 
 Station, Gainesville
 
 BOARD OF CONTROL 
 
 J. B. HODGES, Chairman, Lake City, Fla. 
 
 E. L. WARTMANN, Citra, Fla. 
 
 J. B. SUTTON, Tampa, Fla. 
 
 J. T. DIAMOND,* Tallahassee, Fla. 
 
 H. B. MINIUM, Jacksonville, Fla. 
 
 BRYAN MACK, Secretary, Tallahassee, Fla. 
 
 J. G. KELLUM, Auditor, Tallahassee, Fla. 
 
 *Resigned.
 
 CITRUS FERTILIZER EXPERIMENTS 
 
 By S. E. COLLISON 
 
 The judicious use of commercial fertilizers in the orange grove 
 has been one of the important problems confronting the Florida 
 citrus grower. In the expense involved and the effects upon the 
 tree and fruit, this problem ranks as of equal importance with 
 any of the other operations in the grove, such as spraying, har- 
 vesting, pruning or cultivation. At the time when the work re- 
 ported in this bulletin was begun, practically no experimental 
 work in this line had been carried out in the state. The existing 
 knowledge of the effects of the various fertilizers in use was 
 entirely the result of the practical experience of the growers 
 themselves and was of a more or less conflicting nature. In order 
 to obtain accurate knowledge of the effects of various fertilizers 
 over a comparatively long period, the experimental work dis- 
 cussed in this bulletin was undertaken. A young grove was 
 located on Lake Harris, about three miles from Tavares, in Lake 
 county, and used for the experiment. The piece of land was 
 selected with special reference to protection from cold, adapta- 
 bility to citrus culture and uniformity of type of soil. It is gen- 
 erally considered that the influence of the fertilizer treatment 
 given citrus trees may extend over a period of several years after 
 that particular treatment has been discontinued. In order to elim- 
 inate this disturbing factor from the experiment it was deemed 
 advisable to begin with young trees. Accordingly, one year old 
 budded trees, all of the same variety, especially selected with 
 regard to uniformity of size, and all from the same nursery, 
 were used in the work. They were set out in January, 1909, three- 
 quarters of a pound of bone meal being given each tree. 
 
 OBJECTS OF THE EXPERIMENT 
 
 The objects of the experiment were to determine the effects 
 of various fertilizers upon the chemical composition of the soil, 
 upon the growth and composition of the trees and upon the fruit. 
 The effects of lime and other alkaline materials, and of various 
 cultural treatments upon the soil and upon the trees were also 
 objects of study. To supplement the work in the grove with 
 fertilizers, a number of soil tanks were made use of on the horti- 
 cultural grounds of the Experiment Station. 
 
 PLAN OF EXPERIMENT 
 
 The grove was divided into 48 plots of ten trees each. These 
 trees were Valencia Late on sour stock, and were set 15 by 30 
 
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 Florida Agricultural Experiment Station 
 
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 Fig. 1. Diagram of plots in the ten year fertilizer experiment 
 
 TABLE 1. FERTILIZER MIXTURES USED 
 An application of two pounds per tree was taken as the standard amount. 
 
 ( Ammonia, 5 per cent., from sulphate of ammonia. 
 
 Standard formula J Phosphoric acid, 6 per cent., from acid phosphate, 
 (for young trees) I Potash, 6 per cent., from high-grade sulphate of 
 potash.
 
 Bulletin 154, Citrus Fertilizer Experiments 5 
 
 Variations from the Standard 
 
 Plot 1. Half the standard. 
 
 Plot 2. Standard. 
 
 Plot 3. Double the standard. 
 
 Plot 4. Four times the standard. 
 
 Plot 5. Phosphoric acid and ammonia increased by one half. 
 
 Plot 6. Phosphoric acid and potash increased by one half. 
 
 Plot 7. Ammonia and potash increased by one half. 
 
 Plot 8. Phosphoric acid and potash decreased by one half. 
 
 Plot 9. Phosphoric acid and ammonia decreased by one half. 
 
 Plot 10. Ammonia and potash decreased by one half. 
 
 Plot 11. Standard and finely ground limestone. 
 
 Plot 12. Standard and air-slaked lime. 
 
 Plot 13. Standard and mulch. 
 
 Plot 14. Standard. 
 
 Sources of Nitrogen 
 
 Plot 15. From nitrate of soda. 
 
 Plot 16. Half from nitrate of soda, and half from sulphate of ammonia. 
 
 Plot 17. From dried blood. 
 
 Plot 18. Half from sulphate of ammonia, and half from dried blood. 
 
 Plot 19. Half from nitrate of soda, and half from dried blood. 
 
 Plot 20. From cottonseed meal. 
 
 Plot 21. From cottonseed meal. (With ground limestone.) 
 
 Plot 22. Half from cottonseed meal, and half from sulphate of ammonia. 
 
 Plot 23. Half from cottonseed meal, and half from nitrate of soda. 
 
 Sources of Phosphoric Acid 
 Plot 24. From dissolved boneblack. 
 Plot 25. From steamed bone. 
 Plot 26. From steamed bone. (Double amount.) 
 Plot 27. From Thomas' slag. (Nitrogen from nitrate of soda.) 
 Plot 28. From Thomas' slag. (Double amount. Nitrogen from nitrate of 
 
 soda.) 
 Plot 29. From acid phosphate. (Potash, 7% per cent, in June, 7% in 
 
 October, and 3 in February.) 
 Plot 30. From acid phosphate. (Nitrogen from nitrate of soda. Potash 
 
 from hardwood ashes.) 
 
 Plot 31. From acid phosphate. (Standard.) 
 Plot 32. From dissolved boneblack. 
 Plot 33. From floats. 
 Plot 34. From floats. (Double amount.) 
 Plot 35. From floats. (Four times amount.) 
 Plot 36. From floats. (Four times amount. Nitrogen from cottonseed 
 
 meal.) 
 
 Sources of Potash 
 
 Plot 37. From low-grade sulphate. 
 
 Plot 38. From muriate. 
 
 Plot 39. From high-grade sulphate of potash. (With ground limestone.) 
 
 Plot 40. From kainit. 
 
 Plot 41. From high-grade sulphate of potash. (Standard.) 
 
 Plot 42. From nitrate of potash. (Balance of nitrogen from nitrate of 
 soda.) 
 
 Variations from the Standard 
 
 Plot 43. No fertilizer. 
 
 Plot 44. Standard. 
 
 Plot 45. Standard and mulch. 
 
 Plot 46. Standard and clean culture. 
 
 Plot 47. Nitrogen from dried blood. Clean culture. 
 
 Plot 48. Nitrogen from nitrate of soda. Clean culture.
 
 6 
 
 Florida Agricultural Experiment Station 
 
 feet. The diagram in Figure 1 shows the relation of the plots to 
 each other. The fertilizer and other treatment given these forty- 
 eight plots is shown in Table 1. A standard formula consisting 
 of 5 percent ammonia, 6 percent phosphoric acid, and 6 percent 
 potash, was used. In the fall this was changed to 21/2 percent 
 ammonia and 8 percent potash, the phosphoric acid remaining 
 the same. The standard mixture consisted of sulphate of am- 
 monia, acid phosphate, and high grade sulphate of potatsh. As 
 shown in Table 1 this mixture was varied for different plots by 
 substituting other sources of the three essential elements for 
 those in the standard mixture. The standard mixture was used 
 at first at the rate of 2 pounds per tree three times a year. This 
 amount was gradually increased so that at the end of the experi- 
 ment the "standard" plots were receiving an application of six 
 pounds instead of two. 
 
 TABLE 2. COMPOSITION OF GROVE SOIL. ANALYSIS OF COMPOSITE SAMPLE 
 
 Soil 
 
 Subsoil 
 
 Insoluble matter 
 
 94.09 
 
 94.81 
 
 Volatile matter 
 
 2.55 
 
 1.71 
 
 Nitrogen 
 
 .033 
 
 .018 
 
 Phosphoric acid 
 
 .10 
 
 .09 
 
 Potash 
 
 .047 
 
 .025 
 
 Soda 
 
 .134 
 
 .115 
 
 Lime 
 
 .13 
 
 .17 
 
 Magnesia . . .. 
 
 .14 
 
 .09 
 
 Manganese oxide 
 
 .10 
 
 .14 
 
 Ferric oxide . . 
 
 .98 
 
 .96 
 
 Aluminum oxide 
 
 2.30 
 
 2.40 
 
 Sulphur trioxide 
 
 trace 
 
 trace 
 
 Carbon dioxide 
 
 none 
 
 none 
 
 
 P2O5 
 
 
 1st foot 
 
 .12 
 
 
 2nd foot 
 
 .10 
 
 
 3rd foot 
 
 .09 
 
 
 4th foot 
 
 .09 
 
 
 5th foot 
 
 .09 
 
 
 N_ 
 .030 
 .015 
 .013 
 .012 
 .009 
 
 Plots 46, 47 and 48 were cultivated during the entire year. 
 Plots 13 and 45 were mulched with a mixture of forest leaves, 
 grass, etc. The remainder of the grove was cultivated up to 
 the rainy season (about June 1), and then a cover crop allowed 
 to occupy the land until in September, when it was either turned 
 under or cut for hay and the stubble plowed under. During the 
 early years of the experiment this cover crop consisted of beg- 
 garweed. The soil finally became too acid to support a good crop 
 of the beggarweed, and was at first supplemented with cowpeas, 
 and later on with velvet beans.
 
 Bulletin 154, Citrus Fertilizer Experiments 
 
 TABLE 3. NITROGEN AND PHOSPHORIC ACID IN SOIL 
 
 
 A 
 
 B 
 
 c 
 
 D 
 
 E 
 
 N 
 P2O5 
 
 .029 
 .09 
 
 .040 
 .12 
 
 .033 
 .08 
 
 .033 
 .11 
 
 .037 
 .12 
 
 F 
 
 G 
 
 Ave. 
 
 .030 
 .10 
 
 .028 
 .09 
 
 .033 
 .10 
 
 SUBSOIL 
 
 N 
 P205 
 
 .018 
 .09 
 
 .018 
 .12 
 
 .015 
 .08 
 
 .020 
 .09 
 
 .019 
 .11 
 
 .018 
 .08 
 
 .016 
 .08 
 
 .018 
 .09 
 
 The effects of the various treatments on the trees were meas- 
 ured by taking at regular intervals the diameter of the trunks 
 six inches above the bud. Notes on the size, general appearance 
 and character of growth of the trees were taken from time to 
 time. 
 
 COMPOSITION OF SOIL 
 
 The soil on which the grove is located is a rather coarse reddish 
 sand of the hammock type, verging on high pine, and rather 
 dry in character. At the time that the trees were set out com- 
 posite samples of the soil (0-9 inches) and of the sub-soil (9-21 
 inches) were taken and analyzed. In one place in the field 
 samples of the first five feet were taken and the phosphoric 
 acid and nitrogen contained in the samples were determined. 
 These analyses are given in Table 2. Samples of the soil and 
 subsoil were also taken in seven different places in the field and 
 analyzed for phosphoric acid and nitrogen. These analyses are 
 given in Table 3. They show that the soil over the field was of 
 a fairly uniform composition. The analyses of this soil as a 
 whole indicate that it is somewhat above the average in fertility 
 as compared with citrus soils in general. 
 
 Fip. 2. Sectional view of tai.ks
 
 Florida Agricultural Experiment Station 
 
 Fig. 3. Ground plan of tanks 
 
 LEACHING OF FERTILIZER 
 
 In order to supplement the work with fertilizer in the field, 
 soil tank experiments were begun on the Station grounds. 
 By this means it has been possible to more closely measure and 
 control conditions than where the work has been conducted on 
 the scale necessary in field experiments. Accurate estimates 
 of the losses of fertilizing materials in the drainage water under 
 different systems of fertilizing and the effect of long continued 
 use of fertilizers on the soil have been possible. In this way much 
 interesting light has been thrown upon the question of the 
 capacity of the average sandy Florida soil for retaining the 
 fertilizing ingredients added to it and which of these materials 
 are most subject to leaching. 
 
 Figures 2 and 3 illustrate the equipment used in the work. 
 The tanks were constructed of heavy galvanized iron, painted
 
 Bulletin 154, Citrus Fertilizer Experiments 9 
 
 inside and out with a chemically-resistant paint. Each tank had 
 an inside diameter of 5 feet 3*4 inches, with a maximum depth 
 of 4 l /2 feet, and a surface area of one two-thousandths of an 
 acre. As shown in the diagram, the bottom of the tank slopes 
 to one side, where there is a strainer opening into a two inch 
 tin-lined iron drainage pipe, the length of which is a little over 
 4 feet. Four such tanks open into a central collecting pit as 
 shown in Figure 3. Under the ends of the drainage pipes 
 entering at the four corners of the pit were placed large gal- 
 vanized cans for collecting the drainage waters. These cans 
 were coated on the inside with paraffine to prevent any chemical 
 action of the drainage water upon the metal. The collecting pit, 
 which is about 8 feet deep and 6 feet square inside, is built of 
 brick, with a concrete bottom, and is covered. The soil tanks 
 were sunk in the ground to within a few inches of the tops and 
 were filled with soil to within 3 inches of the rims. The soil 
 used was a rather coarse, gray sand of high hammock type. It 
 is described "by the Bureau of Soils as Norfolk sand. In filling 
 the tanks a layer of quartz pebbles was first placed over the 
 sloping part of the bottom in order to provide adequate drainage 
 and to prevent the soil from sifting thru the strainer and filling 
 the drainage pipe. Above the layer of pebbles was placed 45 
 inches of soil. In excavating for the tanks the soil was removed 
 in layers. First a 9 inch layer was removed and placed at one 
 side by itself. Then the soil was removed in one foot layers, each 
 foot being kept separate from the remainder. The last foot of 
 excavated soil was placed in the bottom of the tank, then the 
 remaining sections ending with the top 9 inches. Thus the 
 soil rested in the tank as it was in the original state. Each layer 
 of soil was well packed as it was placed in the tank, the same 
 weight of dry soil, 8,625 pounds, being used in each. The tanks 
 were then exposed to natural conditions, the drainage water 
 leaching thru the soil being collected from time to time as it 
 became necessary, and analyzed. This treatment was continued 
 for a period of 10 months during which time the soil received no 
 fertilizer, the results obtained representing the losses of plant 
 food from a bare, unfertilized soil. The results show that by far 
 the greatest loss of plant food falls on the nitrogen of the soil. 
 The thoro aeration which the soil received when the tanks were 
 filled would lead to more rapid nitrification of the soil organic 
 matter and thus to somewhat larger losses of nitrogen in the 
 drainage water at first, than would occur under natural condi-
 
 10 
 
 Florida Agricultural Experiment Station 
 
 TABLE 4. Loss OF NITROGEN FROM SOIL TANKS 
 
 Water 
 sampled 
 
 g-o 
 
 
 
 23 
 
 n 
 
 a* 
 
 Sulphate of 
 Ammonia 
 
 Nitrate of 
 Soda 
 
 Dried Blood 
 
 4J 
 
 
 O 
 
 
 
 Q 
 
 w 
 
 
 fc 
 
 c~ 
 
 Is 
 
 ^ " 
 
 z 
 
 -j 
 
 09 
 
 jD 
 
 fc 
 
 '8 
 
 to 
 
 .S 
 fc 
 
 c^ 
 g 
 ",2 
 *-i^ 
 
 fifc 
 3.05 
 15.63 
 33.28 
 54.21 
 35.44 
 10.59 
 16.04 
 20.95 
 18.10 
 
 *> 
 
 01 
 
 
 fc 
 
 1 
 
 .5 
 
 fc 
 
 Is 
 
 & 
 
 July 13 
 Aug. 23 
 Sept. 5 
 Nov. 22 
 Jan. 8 
 Mar. 12 
 April 13 
 June 10 
 July 16 
 Aug. 23 
 Oct. 21 
 April 1 
 July 14 
 Aug. 9 
 Oct. 31 
 Jan. 3 
 Jan. 24 
 Feb. 11 
 Mar. 6 
 Aug. 8 
 Oct. 10 
 Oct. 23 
 Dec. 21 
 Jan. 6 
 Jan. 25 
 April 5 
 May 17 
 
 74.74 
 
 .63 
 1.18 
 4.66 
 8.46 
 8.12 
 5.72 
 3.91 
 10.14 
 9.64 
 6.43 
 3.19 
 .65 
 1.61 
 
 74.11 
 72.93 
 68.27 
 78.49 
 70.36 
 64.64 
 98.09 
 87.95 
 115.68 
 109.25 
 124.75 
 161.46 
 159.85 
 197.23 
 
 .85 
 1.59 
 6.39 
 12.40 
 10.35 
 8.13 
 6.05 
 10.34 
 10.96 
 5.55 
 2.92 
 .52 
 1.00 
 
 2.28 
 11.32 
 20.34 
 22.07 
 13.26 
 2.56 
 3.46 
 11.63 
 7.94 
 
 72.46 
 61.14 
 40.79 
 37.41 
 24.15 
 21.59 
 55.50 
 43.87 
 73.29 
 73.29 
 
 1.47 
 4.16 
 11.98 
 16.59 
 9.35 
 2.06 
 .43 
 2.10 
 1.99 
 
 73.27 
 69.11 
 57.13 
 59.22 
 49.87 
 47.81 
 84.75 
 82.65 
 118.02 
 118.02 
 
 1.96 
 5.68 
 17.34 
 29.05 
 15.80 
 4.13 
 .90 
 2.48 
 2.41 
 
 
 18.69 
 
 37.37 
 
 37.37 
 
 
 18.69 
 37.37 
 37.37 
 
 3.46 
 4.23 
 2.38 
 
 88.52 
 121.65 
 119.28 
 156.65 
 
 4.72 
 4.78 
 1.95 
 
 1.38 
 .97 
 .27 
 
 135.33 
 171.72 
 171.45 
 208.82 
 
 1.17 
 .72 
 .16 
 
 18.69 
 
 2.53 
 1.72 
 .56 
 .59 
 .79 
 2.33 
 3.12 
 
 213.38 
 211.66 
 211.09 
 210.50 
 247.08 
 282.12 
 279.00 
 279.00 
 
 1.28 
 .80 
 .27 
 .28 
 .38 
 .94 
 1.11 
 
 2.17 
 .43 
 .29 
 .84 
 .93 
 4.25 
 1.20 
 
 173.16 
 172.73 
 172.44 
 171.60 
 208.04 
 241.16 
 239.96 
 239.96 
 
 1.39 
 .25 
 .17 
 .48 
 .54 
 2.05 
 .50 
 
 .22 
 .16 
 .27 
 .32 
 .34 
 .27 
 
 227.28 
 227.12 
 22685 
 226.53 
 263.57 
 300.66 
 30066 
 300.41 
 318.69 
 318.44 
 317.92 
 317.47 
 317.47 
 
 .11 
 .07 
 .12 
 .14 
 .15 
 .10 
 
 
 
 37.37 
 37.37 
 
 18.69 
 
 .25 
 .41 
 .25 
 .52 
 .45 
 
 .08 
 .14 
 .08 
 .16 
 .14 
 
 2.26 
 2.28 
 2.03 
 1.49 
 1.02 
 
 295.42 
 293.13 
 291.10 
 289.60 
 288.58 
 
 .81 
 .77 
 .69 
 .51 
 .35 
 
 2.22 
 1.52 
 1.63 
 .86 
 
 256.42 
 254.90 
 253.27 
 252.41 
 252.41 
 
 .92 
 .59 
 .64 
 .34 
 
 
 
 37.37 
 
 tions. Allowing for this factor, however, the losses of nitrogen 
 still remain very large. During the 10 month period a loss of 
 nitrogen equivalent to over 800 pounds nitrate of soda per acre 
 was noted. The losses of potash and phosphoric acid were much 
 smaller, in fact, almost negligible. The loss of potash per acre 
 amounted to about 14 pounds, and phosphoric acid to about a 
 half pound. These figures show that these two elements of plant 
 food are locked up in the soil in relatively insoluble forms which 
 become only slowly available. At the end of this period of 10 
 months, an orange tree was placed in each tank and fertilized 
 with a fertilizer of the same formula as that used in the grove 
 experiment. The trees in all the tanks received the same amounts 
 of phosphoric acid and potash in the form of acid phosphate and 
 high grade sulphate of potash, the source of nitrogen only being 
 varied. The trees in tanks 1 and 2 received sulphate of ammonia, 
 the tree in tank 3 nitrate of soda, the tree in tank 4, dried blood,
 
 Bulletin 154, Citrus Fertilizer Experiments 11 
 
 the same amount of actual nitrogen being used for each tree. 
 The same amount of fertilizer as was used in the grove was 
 applied to each tree three times per year. The results of the 
 analyses of the drainage water collected from these tanks from 
 time to time are given in Table 4. These figures indicate the 
 extent to which the nitrogen of the three materials used leaches 
 thru the soil. These losses are stated here in percentages of the 
 total amount of nitrogen applied less the amounts lost on pre- 
 ceding dates. For example, the table shows that on November 
 22, 1911, the drainage water from the nitrate of soda tank 
 contained an amount of nitrogen equivalent to over 54 percent 
 of the total nitrogen which had been applied up to that date, 
 less the quantity of nitrogen already leached out up to the 
 same date. In other words, the percentage of loss for each 
 date was figured on the amount of nitrogen still remaining in 
 the soil at that date, and not on the total amount which had 
 been applied. 
 
 LOSS OF NITROGEN 
 
 A study of the table brings out a number of interesting and 
 important facts. It will be noted that while the loss of nitrogen 
 varies with the material used, the percentages lost with all three 
 materials increase from the beginning up to November 22, and 
 continue large until August, 1913. For the period from July 
 13, 1911 to July 17, 1913, 41 percent of the sulphate of ammonia 
 applied to the soil leached thru and was lost in the drainage 
 water; 72.5 percent of the nitrate of soda, and 38.3 percent of 
 the dried blood were lost. This interval of about two years 
 represents a period during which the trees were becoming estab- 
 lished and when the root system was small and occupied but a 
 small portion of the soil. Consequently, much of the fertilizer 
 was not utilized and as a result leached thru the soil and was 
 lost. The fact that the losses became smaller as time went on 
 indicates that the larger root systems were able to utilize more 
 and more of the fertilizer. The table also brings out important 
 differences in the behavior of the three different sources of 
 nitrogen in the soil. It will be noted that the largest loss of 
 nitrogen occurred with the nitrate of soda, the losses from the 
 other two sources being considerably less. The larger loss of 
 nitrate of soda is explained by the fact that this material is 
 very readily soluble in the soil moisture and that the soil has 
 very little if any power to retain or fix nitrogen in the nitrate 
 form. Consequently, if the soil is moist and the rainfall is
 
 12 Florida Agricultural Experiment Station 
 
 sufficient to more than saturate the soil the nitrate of soda is 
 immediately dissolved and much of it is carried below the range 
 of the plant roots. Dried blood and sulphate of ammonia differ 
 from nitrate of soda in their behavior in the soil. 
 
 The nitrogen in these materials is not available for plants 
 until it is changed to the nitrate form thru the agency of various 
 soil bacteria in the process known as nitrification. In its original 
 form the nitrogen of dried blood is not readily soluble in the 
 soil water, and consequently very little is lost in the leaching 
 process until nitrification occurs. In this change the organic 
 nitrogen of the blood is changed first to ammonia, then to the 
 nitrite and finally to the nitrate form, when it becomes as 
 readily soluble as the nitrate of soda and is leached out as 
 readily. Nitrification of the dried blood is a gradual process, 
 extending over a period of time which may be of several weeks' 
 duration, depending on soil conditions. Because of this, some 
 of the nitrogen of dried blood, or for that matter, any similar 
 organic material, will remain in the soil a considerably longer 
 time and be available to the crop over a longer period, than 
 nitrate of soda. This is especially true where heavy rains occur 
 after the latter has been applied to the soil. 
 
 The behavior of sulphate of ammonia in the soil is different 
 from either of the two materials already discussed. While this 
 substance is readily soluble in the soil water the soil has the 
 power of fixing or absorbing at least a portion of the ammonia, 
 thus preventing it from leaching away. This takes place thru 
 chemical means and is common to all soils. Very sandy soils can 
 absorb only a small amount of ammonia; loam and clay soils 
 are able to absorb much larger quantities, due mainly to the clay 
 content of these soils. Therefore, when sulphate of ammonia is 
 applied to the soil at least a part of the ammonia is absorbed 
 by this clay present and fixed in a form which is not readily 
 washed out. This ammonia must be changed, thru the agency of 
 the nitrifying bacteria of the soil, to the nitrate form. Then 
 it gradually becomes available to the plant and, of course, is 
 then subject to leaching. These facts account for the smaller 
 loss of nitrogen as noted in the table, from the soil receiving 
 sulphate of ammonia as compared with that receiving nitrate 
 of soda. 
 
 It should be remembered that the three sources of ammonia 
 here discussed were used side by side, in the same equivalent 
 amounts, on the same type of soil and under identical conditions 
 so far as these could be brought about in the experimental work.
 
 Bulletin 154, Citrus Fertilizer Experiments 
 
 13 
 
 Accordingly, the behavior of each of these materials in the soil 
 as compared with the others may be taken as strictly compara- 
 tive not only in this experiment but under all usual conditions 
 where they are used. The actual amount of each which might be 
 lost in the drainage on different types of soil and under varied 
 conditions would in all probability differ more or less from the 
 results given in the table. However, the fact that nitrate of 
 soda for instance, leaches thru to a much larger extent than 
 sulphate of ammonia, would hold true under all ordinary con- 
 ditions. The important facts brought to light in the experimental 
 work here described regarding these nitrogenous materials and 
 which have a practical application in grove fertilization are as 
 follows: Nitrogen, the most expensive ingredient of fertilizers 
 under normal conditions and usually the element most deficient 
 in Florida soils, is the element which is lost in the largest 
 amounts by leaching. 
 
 TABLE 5. Loss OF POTASH BY LEACHING 
 
 Tank 1 
 
 Tank 3 
 
 > a 
 
 > tn 
 
 July 13 
 AU'K. 23 
 Sept. 5 
 Nov. 22 
 Jan. 8 
 Mar. 12 
 April 13 
 June 10 
 July 16 
 AUK. 23 
 Oct. 21 
 April 1 
 July 14 
 AUK- 9 
 Oct. 31 
 Jan. 3 
 Jan. 24 
 Feb. 11 
 Mar. 6 
 AUK. 8 
 Oct. 10 
 Oct. 23 
 Dec. 21 
 Jan. 6 
 Jan. 25 
 April 5 
 May 17 
 
 
 o . 
 
 "S o 
 
 o c 
 
 c o 
 
 _5 
 
 
 
 sS 
 
 
 
 ^0 
 
 : w ^ 
 
 M ) 
 
 -, C^J 
 
 ^1 "^J 
 
 "M 
 
 o s 
 
 
 CH* 
 
 UJ W 
 
 
 108.86 
 
 .10 108.76 
 
 .09 
 
 .30 108.56 
 
 .27 
 
 
 .10 108.66 
 
 .09 
 
 .70 107.86 
 
 .64 
 
 
 .70 107.96 
 
 .64 
 
 1.20 106.66! 
 
 1.11 
 
 72.57 
 
 1.30 179.23 
 
 1.20 
 
 2.30176.93' 
 
 2.15 
 
 
 2.40 176.83 
 
 1.34 
 
 4.20 172.73 
 
 2.37 
 
 54!43 
 
 3.50 173.33 
 
 1.98 
 
 3.90 168.83 
 
 2.26 
 
 
 2.90 224.86 
 
 1.67 
 
 4.10219.16 
 
 2.43 
 
 54.43 
 
 9.60 215.26 
 
 4.27 
 
 8.40210.76 
 
 3.83 
 
 
 11.80257.89 
 
 5.48 
 
 4.30 260.89 
 
 2.04 
 
 
 10.80247.09 
 
 4.19 
 
 260.89 
 
 
 72.57 
 
 11.10308.56 
 
 4.49 
 
 12.20321.26! 
 
 4.68 
 
 54.43 
 
 7.10355.89 
 
 2.30 
 
 6.80 368.89 
 
 2.11 
 
 54.43 
 
 6.50 349.39 
 
 1.83 
 
 6.60 362.29 
 
 1.79 
 
 
 403. S2 
 
 
 . 416.72 
 
 
 72.57 
 
 10.10466.29 
 
 2.50 
 
 17.00472.29 
 
 4.08 
 
 
 16.00450.29 
 
 3.43 
 
 22.50 449.79 
 
 4.76 
 
 
 7.50 442.79 
 
 1.66 
 
 14.70435.09 
 
 3.27 
 
 
 7.00 435.79 
 
 1.58 
 
 11 20423.89 
 
 2.57 
 
 54.43 
 
 8.30 481.92 
 
 1.90 
 
 10.20 46S. 12 
 
 2.41 
 
 54.43 
 
 13.40522.95 
 
 2.78 
 
 11.20 511.35 
 
 2.39 
 
 
 19.80503.15 
 
 3.79 
 
 6.20 505.15 
 
 1.21 
 
 72.57 
 
 ... 503.15 
 
 
 505.15 
 
 
 
 14.60561.12 
 
 2.90 
 
 13.40 564.32 
 
 2J55 
 
 
 12.40548.72 
 
 2.21 
 
 11.40 552.92 
 
 2.02 
 
 
 13.40535.32 
 
 2.44 
 
 11.80 541.12 
 
 2.13 
 
 54.43 
 
 16 50 518.82 
 
 3.08 
 
 13.90 527.22 
 
 2 57 
 
 
 9.60 573.25 
 
 1 .85 
 
 5S1.65 
 
 
 Tank 4 
 
 .40 
 
 .50 
 
 .80 
 
 .80 
 
 1.10 
 
 2.20 
 
 2.00 
 
 5.40 
 
 3.90 
 
 5.10 
 6.60 
 6.90 
 
 ""3/20 
 
 6.70 
 
 10.90 
 
 13.60 
 
 10.20 
 
 5.50 
 
 3.90 
 
 10.30 
 
 8.40 
 
 8.10 
 
 12.00 
 
 108.46 
 
 107.96 
 
 107.16! 
 
 178.93 
 
 177.83 
 
 175.63 
 
 228.06 
 
 222.66 
 
 273.19 
 
 273.19 
 
 340.66 
 
 388.49 
 
 381.59 
 
 436.02 
 
 505.39 
 
 498. 69 
 
 487.79 
 
 474.19 
 
 518.42 
 
 567.35 
 
 567.35 
 
 563.45 
 
 625.72 
 
 617.32 
 
 609.22 
 
 597.22 
 
 651.65 
 
 .37 
 
 .46 
 
 .74 
 
 .74 
 
 .61 
 
 1.24 
 
 1.14 
 
 2.37 
 
 1.75 
 
 1.86 
 1.94 
 
 1.77 
 
 !?3 
 
 1.32 
 2.18 
 2.79 
 2.15 
 1.06 
 
 .69 
 1.83 
 1.34 
 1 .3 1 
 1.97
 
 14 Florida Agricultural Experiment Station 
 
 The various sources of nitrogen differ greatly in their tendency 
 to leach out of the soil, much more of the nitrogen of nitrate of 
 soda than of sulphate of ammonia being lost in this way. 
 
 The greatest losses take place when heavy rains occur soon 
 after an application of nitrogenous fertilizers. 
 
 These losses decrease to a great extent as the trees become 
 older and more of the soil becomes permeated with tree roots. 
 
 LOSS OF POTASH 
 
 Table 5 shows that a considerable loss of potash has taken 
 place. The figures in the potash column represent the average 
 losses for three soil tanks. The losses for the first two years 
 are small, after which they increase considerably. This would 
 indicate that during the first period part of the potash applied 
 was absorbed by the soil, but that after the second year the 
 soil had reached its maximum capacity for holding the potash 
 and became saturated, so to speak, so that succeeding applica- 
 tions were not absorbed to any extent. 
 
 It is well known that practically all soils have some power to 
 retain soluble potash. Sandy soils exhibit this capacity in the 
 least degree, while heavy clay soils will absorb large amounts. 
 The power of a soil to fix or absorb potash depends largely upon 
 the presence of certain silicates which are associated with the 
 clay present. When absorbed by the soil, water-soluble potash 
 assumes a form which is not easily leached out by water but 
 which is still generally regarded as being more available to 
 plants than the potash combinations originally present. Since 
 Florida soils as a general rule contain very little clay their power 
 to absorb potash is limited. In the work here described it was 
 found that at the end of four years about 30 percent of the 
 potash applied had leached out, the remaining 70 percent being 
 used by the trees or absorbed by the soil. In bearing groves the 
 loss by leaching would undoubtedly be under rather than over 
 the 30 percent found here. 
 
 LOSS OF PHOSPHORIC ACID 
 
 No table is included to show the loss of phosphoric acid since 
 this loss has been extremely small. At the end of four years it 
 was found that only .05 of one percent of the amount applied was 
 lost in the drainage water. This indicates that the soil is able 
 to absorb large amounts of soluble phosphoric acid. That this 
 is true is shown by the fact that the soil used contained 50 per- 
 cent more phosphoric acid at the end of five years than it did at 
 the beginning of the experiment.
 
 Bulletin 154, Citrus Fertilizer Experiments 
 TABLE 6. INCREASE IN PHOSPHORIC ACID CONTENT OP SOIL 
 
 15 
 
 o 
 
 E 
 1 
 
 Source of 
 Phosphoric Acid 
 
 Acid phosphate 
 
 o-g 
 
 (M-5 
 
 PL, CM 
 2859 
 
 . 
 
 O a) 
 
 2633 
 
 S3 
 
 a "o 
 
 226" 
 
 . Increase 
 
 tO . A J 
 
 o in Acid- 
 
 Snliihlft 
 
 2 
 
 Acid phosphate 
 
 3601 
 
 3002 
 
 599 
 
 480 
 
 3 
 
 Acid phosphate 
 
 4532 
 
 3449 
 
 1083 
 
 850 
 
 4 
 
 Acid phosphate 
 
 4750 
 
 3037 
 
 1713 
 
 1660 
 
 5 
 
 Acid phosphate 
 
 3701 
 
 3037 
 
 664 
 
 750 
 
 6 
 
 Acid phosphate 
 
 4080 
 
 3449 
 
 631 
 
 720 
 
 7 
 
 Acid phosphate 
 
 3513 
 
 3002 
 
 511 
 
 450 
 
 8 
 
 Acid phosphate 
 
 3082 
 
 2633 
 
 449 
 
 300 
 
 9 
 
 Acid phosphate 
 
 3720 
 
 3238 
 
 482 
 
 320 
 
 10 
 
 Acid phosphate 
 
 3213 
 
 2895 
 
 318 
 
 310 
 
 11 
 
 Acid phosphate 
 
 3783 
 
 3356 
 
 427 
 
 390 
 
 12 
 
 Acid phosphate 
 
 3357 
 
 3177 
 
 180 
 
 380 
 
 13 
 
 Acid phosphate 
 
 3916 
 
 3177 
 
 739 
 
 630 
 
 14 
 
 Acid phosphate 
 
 3659 
 
 3356 
 
 303 
 
 440 
 
 15 
 
 Acid phosphate 
 
 3396 
 
 2895 
 
 501 
 
 530 
 
 16 
 
 Acid phosphate 
 
 4372 
 
 3469 
 
 903 
 
 600 
 
 17 
 
 Acid phosphate 
 
 4286 
 
 3794 
 
 492 
 
 290 
 
 18.. . 
 
 Acid phosphate 
 
 3861 
 
 3554 
 
 307 
 
 280 
 
 19 
 
 Acid phosphate 
 
 3598 
 
 2959 
 
 639 
 
 450 
 
 20. 
 
 Acid phosphate 
 
 3472 
 
 2839 
 
 633 
 
 310 
 
 21. . 
 
 Acid phosphate 
 
 3456 
 
 2839 
 
 617 
 
 410 
 
 22 
 
 Acid phosphate 
 
 3516 
 
 2959 
 
 557 
 
 630 
 
 23 . 
 
 Acid phosphate . 
 
 4210 
 
 3554 
 
 656 
 
 370 
 
 24.. . 
 
 Dis. bone black 
 
 4115 
 
 3794 
 
 321 
 
 430 
 
 25 
 
 Steamed bone 
 
 3609 
 
 3098 
 
 511 
 
 230 
 
 26 
 
 Steamed bone 
 
 4524 
 
 3651 
 
 873 
 
 510 
 
 27 
 
 Basic slag 
 
 3643 
 
 3033 
 
 610 
 
 340 
 
 28 
 
 Basic slag 
 
 3901 
 
 3236 
 
 665 
 
 630 
 
 29 
 
 Acid phosphate 
 
 3559 
 
 3236 
 
 323 
 
 340 
 
 30 
 
 Acid phosphate 
 
 3434 
 
 3037 
 
 397 
 
 400 
 
 31 
 
 Acid phosphate 
 
 4145 
 
 3651 
 
 494 
 
 440 
 
 32 
 
 Dis. bone black 
 
 3530 
 
 3098 
 
 432 
 
 450 
 
 33 
 
 Floats 
 
 3197 
 
 2904 
 
 293 
 
 330 
 
 34 
 
 Floats 
 
 4095 
 
 3191 
 
 904 
 
 650 
 
 35 
 
 Floats 
 
 4091 
 
 3035 
 
 1056 
 
 1010 
 
 36 
 
 Floats 
 
 4466 
 
 2795 
 
 1671 
 
 1400 
 
 37 
 
 Acid phosphate 
 
 3270 
 
 2795 
 
 475 
 
 420 
 
 38 
 
 Acid phosphate 
 
 3877 
 
 3035 
 
 842 
 
 540 
 
 39 
 
 Acid phosphate 
 
 3507 
 
 3191 
 
 316 
 
 420 
 
 40 
 
 Acid phosphate 
 
 3529 
 
 2904 
 
 625 
 
 510 
 
 41. 
 
 Acid phosphate 
 
 3432 
 
 2997 
 
 435 
 
 300 
 
 42 
 
 Acid phosphate 
 
 3510 
 
 2820 
 
 690 
 
 520 
 
 43.. . 
 
 No fertilizer 
 
 3348 
 
 3348 
 
 
 
 30 
 
 44.. . 
 
 Acid phosphate 
 
 3815 
 
 3142 
 
 673 
 
 380 
 
 45.. 
 
 Acid phosphate 
 
 3735 
 
 3142 
 
 593 
 
 490 
 
 46 
 
 Acid phosphate 
 
 3716 
 
 3348 
 
 368 
 
 320 
 
 47 
 
 Acid phosphate . 
 
 3192 
 
 2860 
 
 332 
 
 400 
 
 48.... 
 
 Acid nhosnhate .. 
 
 3529 
 
 2997 
 
 532 
 
 460 
 
 PHOSPHORIC ACID 
 
 In studying the effect of the fertilizers used on the composition 
 of the soil, especial attention was given to the phosphoric acid. 
 Work at the Experiment Station with soil tanks has shown that 
 the loss of phosphoric acid in the drainage water where acid
 
 16 Florida Agricultural Experiment Station 
 
 phosphate was used was so small as to be negligible, and that 
 practically all the phosphoric acid applied was retained by the 
 soil. The work with the grove soils has confirmed these results. 
 Samples of soil from the fertilized plots and from the middle of 
 the tree rows were taken from time to time to a depth of 9 inches, 
 and determinations made of the phosphoric acid. Work else- 
 where has shown that the greater part of the phosphoric acid 
 absorbed by soils is retained in the upper plowed soil, so in this 
 work sampling to a depth of 9 inches was considered sufficient. 
 The difference between the amount of phosphoric acid in the 
 soil of the plot and that in the corresponding middle would show 
 the quantity fixed by the soil. These results for the different 
 plots are given in Table 6. In order to make the results easily 
 comparable they have been calculated to pounds per acre. The 
 figures in the table represent in every instance the average of 
 the results obtained from three different samplings of soil, the 
 third being taken in July, 1915. The second column from the 
 right shows the increase in phosphoric acid content, due to the 
 absorption by the soil of the phosphate fertilizer applied. It 
 will be noted that these figures vary considerably among them- 
 selves, even where the amount and form of phosphoric acid 
 applied has been identical. This variation can be accounted for 
 by the difficulty of obtaining samples of soil which are perfectly 
 representative of the plots. However, it will be noted that those 
 plots receiving the largest applications of fertilizer also show 
 the greatest amounts of phosphoric acid retained. Plot 4, re- 
 ceiving four times the standard quantity of fertilizer shows 
 the greatest fixation, an increase of 1713 pounds per acre being 
 noted. The source of the phosphoric acid on this plot was acid 
 phosphate. Plot 36 receiving the same amount of actual phos- 
 phoric acid as plot 4, but in the form of floats, shows a gain 
 practically the same as plot 4. Both these plots show an increase 
 of over 50 percent. Altho five different sources of phosphoric 
 acid were used on the plots, the form in which it was used does 
 not appear to have had any influence on the power of the soil 
 to absorb this material, the water-soluble form being retained 
 as thoroly as the insoluble forms. 
 
 CHANGES OF PHOSPHORIC ACID IN SOIL 
 
 It is believed that the figures in the last column of Table 6 
 throw some light on the question as to what forms the phos- 
 phoric acid assume after being incorporated with the soil. It is 
 generally agreed upon among soil investigators that the phos-
 
 Bulletin 154, Citrus Fertilizer Experiments 17 
 
 phoric acid of the soil exists mainly in three forms, namely, the 
 phosphates of lime, iron, and alumina. It is generally considered 
 that the last two forms are much less available to plants than 
 the first form. Indeed it is held by many that the phosphates 
 of iron and alumina are but very slightly available because of 
 their practical insolubility in the soil water. Phosphate of lime, 
 on the other hand, dissolves slowly in the soil water containing 
 carbonic acid gas and other weak acids and is thus considered 
 more available to plants. The fixation of soluble phosphoric acid 
 in the soil is explained by the fact that it combines with one or 
 more of the compounds of iron, aluminum or lime present and 
 thus assumes an insoluble form. It then becomes a matter of 
 some practical importance to know whether the phosphoric acid 
 added to the soil assumes the form of the insoluble iron and 
 aluminum phosphates or the more readily available phosphate of 
 lime. A method of treatment which it is believed will distinguish 
 between the different forms has been developed by soil chemists 
 and has been used to some extent. It depends upon digesting the 
 soil in a weak solution of nitric acid, which will dissolve the 
 phosphate of lime present but which has no effect upon the 
 phosphate of iron and alumina. A given weight of soil was 
 treated with fifth-normal nitric acid (about 1.26 percent acid) 
 and the amount of phosphoric acid dissolved out determined, this 
 dissolved phosphoric acid being regarded as coming entirely 
 from the phosphate of lime present. The soil samples used were 
 those on which the total phosphoric acid had been determined as 
 shown in the table. The results given in the table represent the 
 difference between the amounts dissolved from the plot soils 
 and those of the corresponding middles, thus representing the 
 increase in the acid soluble phosphoric acid of the fertilized 
 plots, and are calculated to pounds per acre. 
 
 Some interesting facts are brought out by comparing these 
 results with the figures representing the increase in total phos- 
 phoric acid. Those plots showing the greatest increase in total 
 phosphoric acid also show the greatest increase in acid-soluble. 
 Plot 4 again shows the greatest increase, followed by plot 36. 
 The average increase in acid-soluble phosphoric acid for all the 
 plots (omitting plot 43) is 494 pounds, as compared with an 
 average increase in total of 586 pounds. Assuming that the 
 acid used dissolved out only phosphate of lime and no iron or 
 aluminum phosphate, these figures indicate that about 80 percent 
 of the increase in phosphoric acid content in the plots has been 
 fixed in the form of phosphate of lime.
 
 18 
 
 Florida Agricultural Experiment Station 
 
 TABLE 7. NITROGEN CONTENT OF PLOT SOILS 
 
 Plot 
 
 : Nitrogen 
 
 in Plot 
 
 Nitrogen 
 in Middle 
 
 Plot 
 
 Nitrogen 
 in Plot 
 
 Nitrogen 
 in Middle 
 
 1 
 
 1140 
 
 780 
 
 25 
 
 1350 
 
 1020 
 
 2 
 
 1170 
 
 990 
 
 26 
 
 1080 
 
 930 
 
 3 
 
 1080 
 
 1050 
 
 27 
 
 1110 
 
 1080 
 
 4 
 
 810 
 
 1140 
 
 28 
 
 1140 
 
 1140 
 
 5 
 
 870 
 
 1140 
 
 29 
 
 1290 
 
 1140 
 
 6 
 
 1170 
 
 1050 
 
 30 
 
 1020 
 
 1080 
 
 7 
 
 1140 
 
 990 
 
 31 
 
 1230 
 
 930 
 
 8 
 
 1140 
 
 780 
 
 32 
 
 1440 
 
 1020 
 
 9 
 
 1080 
 
 840 
 
 33 
 
 1200 
 
 1050 
 
 10 
 
 990 
 
 1110 
 
 34 
 
 1140 
 
 1050 
 
 11 
 
 1170 
 
 990 
 
 35 
 
 1170 
 
 1140 
 
 12 
 
 1140 
 
 1020 
 
 36 
 
 1230 
 
 1050 
 
 13 
 
 1410 
 
 1020 
 
 37 
 
 1320 
 
 1050 
 
 14 
 
 1440 
 
 990 
 
 38 
 
 1410 
 
 1140 
 
 15 
 
 1410 
 
 1110 
 
 39 
 
 1080 
 
 1050 
 
 16 
 
 1230 
 
 840 
 
 40 
 
 1110 
 
 1050 
 
 17 
 
 1170 
 
 960 
 
 41 
 
 1230 
 
 810 
 
 18 
 
 1260 
 
 1080 
 
 42 
 
 1380 
 
 1140 
 
 19 
 
 1260 
 
 1080 
 
 43 
 
 900 
 
 990 
 
 20 
 
 1230 
 
 990 
 
 44 
 
 1230 
 
 1290 
 
 21 
 
 1320 
 
 990 
 
 45 
 
 1920 
 
 1290 
 
 22 
 
 1350 
 
 1080 
 
 46 
 
 720 
 
 990 
 
 23 
 
 1260 
 
 1080 
 
 47 
 
 780 
 
 1140 
 
 24 
 
 1440 
 
 960 
 
 48 
 
 720 
 
 810 
 
 NITROGEN 
 
 Table 7 gives the amount of nitrogen in pounds per acre to a 
 depth of 9 inches. The soil samples were taken from the plots 
 and from the middles at the end of the experiment in 1918. One 
 fact brought out here is the considerably smaller amount of 
 nitrogen in the clean culture plots, 46, 47 and 48, as compared 
 with the remaining forty-five plots. The average amount of 
 nitrogen in these three plots is 740 pounds per acre, as compared 
 with an average for the others of 1220 pounds an acre, indicating 
 a loss of 480 pounds or 39 percent. This loss must be attributed 
 largely to the effects of the continuous cultivation. This practice 
 leads to more rapid nitrification of the organic nitrogen of the 
 soil, changing the insoluble nitrogen to the soluble nitrate form 
 which is easily leached out. This loss of organic matter also 
 means a decrease in the capacity of the soil for holding moisture 
 and soluble fertilizers added to it. 
 
 The average of the forty-eight soils taken from the middles 
 is 1030 pounds of nitrogen per acre. It is interesting to compare 
 this figure with the average of fifteen samplings taken at the 
 beginning of the experiment in 1909. These samples were taken 
 at various places over the field and probably give a fair average 
 of the nitrogen content at that time. The amount of nitrogen
 
 Bulletin 154, Citrus Fertilizer Experiments 
 
 19 
 
 found in this way was 1080 pounds per acre. This is so close 
 to the average for the middles (1030 pounds) at the end of the 
 experiment that it is reasonable to assume that the unfertilized 
 soil between the tree rows neither gained nor lost in nitrogen 
 during the ten years. In other words, the loss of nitrogen thru 
 leaching was counterbalanced by the addition of nitrogen by 
 means of the leguminous cover crop. The fertilized plots have 
 gained slightly in nitrogen as compared with the soils from the 
 middle of the rows. Omitting the clean culture plots and the no 
 fertilizer plot, the average is 1220 pounds per acre, a gain over 
 the middles of 190 pounds. 
 
 TABLE 8. POTASH CONTENT OF PLOT SOILS AT END OF EXPERIMENT -IN 1918 
 
 Plot 
 
 Potash 
 
 Plot 
 
 Potash 
 
 1 
 
 1620 
 
 25 
 
 2160 
 
 2 
 
 1800 
 
 26 
 
 1530 
 
 3 
 
 2010 
 
 27 
 
 2070 
 
 4 
 
 2040 
 
 28 
 
 1950 
 
 5 
 
 1740 
 
 29 
 
 1620 
 
 6 
 
 1830 
 
 30 
 
 2040 
 
 Y 
 
 1740 
 
 31 
 
 1950 
 
 8 
 
 1740 
 
 32 
 
 2040 
 
 9 
 
 1830 
 
 33 
 
 1440 
 
 10 
 
 1530 
 
 34 
 
 1950 
 
 11 
 
 1740 
 
 35 
 
 1530 
 
 12 
 
 1950 
 
 36 
 
 1830 
 
 13 
 
 1830 
 
 37 
 
 1830 
 
 14 
 
 1950 
 
 38 
 
 2160 
 
 15 
 
 1620 
 
 39 
 
 1440 
 
 16 
 
 1740 
 
 40 
 
 1680 
 
 17 
 
 1530 
 
 41 
 
 1950 
 
 18 
 
 1740 
 
 42 
 
 1830 
 
 19 
 
 2160 
 
 43 
 
 1140 
 
 20 
 
 1950 
 
 44 
 
 1830 
 
 21 
 
 2250 
 
 45 
 
 1620 
 
 22 
 
 1950 
 
 46 
 
 1620 
 
 23 
 
 1440 
 
 47 
 
 1440 
 
 24 .. 
 
 2040 
 
 48 
 
 1530 
 
 Unfertilized soil 1140 
 
 
 
 
 POTASH IN GROVE SOIL 
 
 The amount of potash present in the different plots at the 
 end of the experiment in 1918 is given in Table 8. The results 
 are calculated in pounds per acre to a depth of 9 inches, and 
 represent the total amount of potash in the soil to that depth. 
 The unfertilized middles were also sampled, and potash deter- 
 mined in seven of these soils. The average of these seven soils 
 amounts to 1140 pounds per acre. By comparing this figure with 
 those for the various plots, the increase in the latter due to the 
 potash in the fertilizer may be determined. It will be noted that
 
 20 
 
 Florida Agricultural Experiment Station 
 
 TABLE 9. GAIN IN DIAMETER OF TREES FOR 10 YEARS 
 
 Gain 
 
 Fertilizer Treatment 
 
 139 
 138 
 136 
 134 
 133 
 132 
 130 
 130 
 128 
 127 
 127 
 127 
 126 
 125 
 124 
 124 
 123 
 123 
 122 
 121 
 120 
 118 
 114 
 114 
 114 
 113 
 112 
 112 
 111 
 111 
 
 110 
 110 
 110 
 109 
 109 
 108 
 107 
 106 
 105 
 104 
 103 
 102 
 101 
 96 
 
 90 
 88 
 75 
 65 
 
 Standard. 
 
 One-half standard. 
 
 Standard and air-slaked lime. 
 
 Standard. Mulched. 
 
 Nitrogen from dried blood. Clean culture. 
 
 Standard. Clean culture. 
 
 Nitrogen, % nitrate of soda, % sulphate of ammonia. 
 
 Standard. Mulched. 
 
 Standard. 
 
 Nitrogen from nitrate of soda. Clean culture. 
 
 Potash from low-grade sulphate. 
 
 Phosphoric acid from steamed bone. 
 
 Nitrogen, ^ cottonseed meal, % sulphate of ammonia. 
 
 Phosphoric acid and potash decreased by one-half. 
 
 Acid phosphate, nitrate of soda, hardwood ashes. 
 
 Standard. 
 
 Phosphoric acid and potash increased by one-half. 
 
 Phosphoric acid from floats. (4 times amt.) Cottonseed meal. 
 
 Phosphoric acid from floats. (4 times amt.) 
 
 Phosphoric acid and nitrogen decreased by one-half. 
 
 Potash from muriate. 
 
 Standard. 
 
 Nitrogen from cottonseed meal. Ground limestone. 
 
 Nitrogen, Vz cottonseed meal, Vz nitrate of soda. 
 
 Twice standard. 
 
 Nitrogen from cottonseed meal. 
 
 Phosphoric acid from steamed bone. (2 times amt.) 
 
 Phosphoric acid from dissolved bone black. 
 
 Phosphoric acid from floats. (2 times amt.) 
 
 Potash from nitrate of potash. Balance nitrogen, nitrate of 
 
 soda. 
 
 Nitrogen, Vz nitrate of soda, Vz dried blood. 
 Standard and ground limestone. 
 Phosphoric acid from dissolved bone black. 
 Nitrogen from nitrate of soda. 
 
 Phosphoric acid from Thomas slag. Nitrate of soda. 
 Nitrogen and potash increased by one-half. 
 Phosphoric acid from floats. 
 
 Nitrogen, % sulphate of ammonia, Vz dried blood. 
 IVz percent potash in June, TVz in October, 3 in February. 
 Potash from kainit. 
 Standard. 
 
 Nitrogen and potash decreased by one-half. 
 No fertilizer. 
 Phosphoric acid from Thomas slag. (2 times amt.) Nitrate of 
 
 soda. 
 
 Nitrogen from dried blood. 
 Standard. Ground limestone. 
 
 Phosphoric acid and nitrogen increased by one-half. 
 Four times standard. 
 
 all the fertilized plots show an increase over the unfertilized 
 soil, thus indicating that this soil was able to retain at least 
 a portion of the soluble potash applied. The average increase 
 for the forty-seven plots amounts to 660 pounds per acre, or an 
 increase of over 50 percent for the ten years of the experiment. 
 A large proportion of the potash in the plot soils is held in
 
 Bulletin 154, Citrus Fertilizer Experiments 
 
 21 
 
 a very insoluble form, probably largely as feldspar. Treatment 
 of these soils with strong hydrochloric acid dissolved on the 
 average only 15 percent of the total potash present. 
 TABLE 10. RANK OF PLOTS 
 
 Rank 
 
 1910 
 
 1911 
 
 1912 
 
 1913 
 
 1914 
 
 1915 
 
 1916 
 
 1917 
 
 1918 
 
 1 
 
 40 
 
 46 
 
 46 
 
 47 
 
 2 
 
 2 
 
 2 
 
 2 
 
 2 
 
 2 
 
 30 
 
 47 
 
 47 
 
 46 
 
 1 
 
 47 
 
 1 
 
 1 
 
 1 
 
 3 
 
 45 
 
 35 
 
 35 
 
 36 
 
 47 
 
 1 
 
 46 
 
 47 
 
 12 
 
 4 
 
 41 
 
 41 
 
 41 
 
 37 
 
 46 
 
 13 
 
 13 
 
 48 
 
 13 
 
 5 
 
 29 
 
 44 
 
 48 
 
 13 
 
 13 
 
 12 
 
 12 
 
 12 
 
 47 
 
 6 
 
 24 
 
 36 
 
 2 
 
 41 
 
 36 
 
 48 
 
 47 
 
 13 
 
 46 
 
 7 
 
 26 
 
 48 
 
 36 
 
 48 
 
 41 
 
 36 
 
 48 
 
 25 
 
 16 
 
 8 
 
 5 
 
 37 
 
 37 
 
 12 
 
 12 
 
 37 
 
 45 
 
 46 
 
 45 
 
 9 
 
 13 
 
 43 
 
 22 
 
 22 
 
 37 
 
 46 
 
 25 
 
 8 
 
 31 
 
 10 
 
 35 
 
 16 
 
 44 
 
 2 
 
 45 
 
 22 
 
 37 
 
 31 
 
 48 
 
 11 
 
 31 
 
 22 
 
 30 
 
 35 
 
 48 
 
 30 
 
 22 
 
 37 
 
 37 
 
 12 
 
 22 
 
 2 
 
 43 
 
 30 
 
 22 
 
 41 
 
 36 
 
 9 
 
 25 
 
 13 
 
 23 
 
 8 
 
 42 
 
 31 
 
 30 
 
 25 
 
 30 
 
 36 
 
 22 
 
 14 
 
 43 
 
 42 
 
 12 
 
 45 
 
 44 
 
 35 
 
 31 
 
 11 
 
 8 
 
 15 
 
 47 
 
 6 
 
 13 
 
 38 
 
 21 
 
 31 
 
 41 
 
 35 
 
 30 
 
 16 
 
 19 
 
 30 
 
 1 
 
 44 
 
 38 
 
 21 
 
 8 
 
 6 
 
 41 
 
 17 
 
 36 
 
 45 
 
 38 
 
 34 
 
 43 
 
 44 
 
 35 
 
 22 
 
 6 
 
 18 
 
 42 
 
 26 
 
 20 
 
 8 
 
 35 
 
 38 
 
 11 
 
 30 
 
 36 
 
 19 
 
 17 
 
 25 
 
 31 
 
 26 
 
 8 
 
 45 
 
 9 
 
 44 
 
 35 
 
 20 
 
 30 
 
 38 
 
 8 
 
 43 
 
 9 
 
 11 
 
 6 
 
 45 
 
 9 
 
 21 
 
 21 
 
 12 
 
 16 
 
 21 
 
 29 
 
 6 
 
 16 
 
 16 
 
 38 
 
 22 
 
 49 
 
 11 
 
 34 
 
 29 
 
 31 
 
 43 
 
 21 
 
 20 
 
 44 
 
 23 
 
 37 
 
 19 
 
 26 
 
 25 
 
 23 
 
 9 
 
 26 
 
 24 
 
 21 
 
 24 
 
 14 
 
 34 
 
 6 
 
 23 
 
 16 
 
 29 
 
 29 
 
 23 
 
 23 
 
 25 
 
 15 
 
 31 
 
 29 
 
 42 
 
 32 
 
 23 
 
 38 
 
 32 
 
 3 
 
 26 
 
 8 
 
 33 
 
 33 
 
 20 
 
 42 
 
 8 
 
 32 
 
 29 
 
 20 
 
 27 
 
 27 
 
 39 
 
 23 
 
 32 
 
 25 
 
 16 
 
 23 
 
 26 
 
 26 
 
 28 
 
 44 
 
 20 
 
 11 
 
 6 
 
 24 
 
 32 
 
 44 
 
 21 
 
 32 
 
 29 
 
 32 
 
 24 
 
 32 
 
 28 
 
 20 
 
 34 
 
 20 
 
 38 
 
 34 
 
 30 
 
 34 
 
 29 
 
 19 
 
 1 
 
 11 
 
 26 
 
 24 
 
 42 
 
 42 
 
 31 
 
 6 
 
 1 
 
 45 
 
 33 
 
 6 
 
 24 
 
 3 
 
 3 
 
 19 
 
 32 
 
 38 
 
 7 
 
 25 
 
 9 
 
 39 
 
 15 
 
 34 
 
 19 
 
 11 
 
 33 
 
 35 
 
 13 
 
 7 
 
 11 
 
 34 
 
 20 
 
 19 
 
 15 
 
 24 
 
 34 
 
 4 
 
 27 
 
 21 
 
 39 
 
 33 
 
 42 
 
 43 
 
 10 
 
 15 
 
 35 
 
 3 
 
 9 
 
 39 
 
 24 
 
 26 
 
 28 
 
 28 
 
 14 
 
 27 
 
 36 
 
 25 
 
 32 
 
 9 
 
 19 
 
 15 
 
 10 
 
 42 
 
 34 
 
 7 
 
 37 
 
 16 
 
 14 
 
 24 
 
 7 
 
 7 
 
 3 
 
 15 
 
 27 
 
 33 
 
 38 
 
 10 
 
 23 
 
 14 
 
 3 
 
 3 
 
 33 
 
 27 
 
 33 
 
 18 
 
 39 
 
 18 
 
 21 
 
 27 
 
 10 
 
 19 
 
 39 
 
 33 
 
 43 
 
 29 
 
 40 
 
 40 
 
 3 
 
 3 
 
 15 
 
 10 
 
 19 
 
 7 
 
 18 
 
 40 
 
 41 
 
 11 
 
 5 
 
 28 
 
 18 
 
 14 
 
 27 
 
 10 
 
 7 
 
 14 
 
 42 
 
 21 
 
 28 
 
 10 
 
 14 
 
 40 
 
 7 
 
 14 
 
 40 
 
 10 
 
 43 
 
 9 
 
 17 
 
 40 
 
 27 
 
 17 
 
 14 
 
 18 
 
 41 
 
 43 
 
 44 
 
 12 
 
 10 
 
 15 
 
 40 
 
 27 
 
 40 
 
 40 
 
 28 
 
 28 
 
 45 
 
 28 
 
 40 
 
 17 
 
 16 
 
 18 
 
 18 
 
 39 
 
 17 
 
 17 
 
 46 
 
 2 
 
 15 
 
 5 
 
 5 
 
 28 
 
 5 
 
 17 
 
 39 
 
 39 
 
 47 
 
 1 
 
 18 
 
 18 
 
 17 
 
 5 
 
 17 
 
 5 
 
 5 
 
 5 
 
 48 
 
 7 
 
 4 
 
 4 
 
 4 
 
 4 
 
 4 
 
 4 
 
 4 
 
 4 
 
 EFFECT OF FERTILIZERS ON GROWTH 
 
 The effect of the various fertilizer treatments used in pro- 
 ducing growth was measured each year by taking the diameter 
 of the tree trunks. Table 9 gives the average measurements of
 
 22 Florida Agricultural Experiment Station 
 
 the trees in the various plots at the end of the experiment. The 
 measurements are given in thirty-seconds of an inch. These 
 figures were obtained by subtracting the original diameter of 
 the tree when set out from the final measurement at the end of 
 1918. In each case they are the average of the ten trees in each 
 plot, and give the actual increase made by the trees. Similar 
 measurements were taken every year during the continuation of 
 the experiment. The standing of the different plots from year 
 to year, beginning with 1910 is shown in Table 10. 
 
 In Table 9 the plots are arranged in the order of the increase 
 in growth made at the end of the ten years, the plot making the 
 largest increase being placed at the head of the list. This table 
 brings out the fact that in this experiment a number of sources 
 of materials have proven almost equally valuable in producing 
 growth and that several have had an injurious effect. Among 
 the fertilizers used on the plots making the most growth no 
 single source has shown any remarkable superiority over others 
 used, altho there is a considerable variation in the effect of the 
 different materials. The results of this work emphasize the fact 
 that the citrus grower need not be restricted in his choice of 
 fertilizers to one particular material, but that there are a number 
 of sources of the three essential elements which can be used to 
 advantage. It should be stated that the soil on which this ex- 
 periment was located was somewhat above the average in fer- 
 tility, especially in phosphoric acid content. This fact has served 
 to minimize differences which might otherwise have developed 
 between the fertilizers used and especially the sources of phos- 
 phoric acid. The behavior of plot 43, which received no fertilizer 
 during the time the experiment continued brings out the fact 
 that the soil was unusually well supplied with plant food. How- 
 ever, a study of the table brings out the fact that the plots making 
 the best growth have received the standard mixture of sulphate 
 of ammonia, acid phosphate and high grade sulphate Of potash. 
 Of the best 16 plots, all but one have received acid phosphate as 
 the source of phosphoric acid. The one exception is plot number 
 25, receiving steamed bone and ranking twelfth in the list. All 
 but two plots in these sixteen have received high grade sulphate 
 of potash as the source of potash. The two exceptions are plot 
 number 37 receiving low grade sulphate of potash and plot 
 number 30 receiving hard wood ashes, and ranking eleventh and 
 fifteenth, respectively. Of the five different sources of nitrogen 
 used, all are represented in the best 10 plots. Sulphate of am-
 
 Bulletin 154, Citrus Fertilizer Experiments 23 
 
 monia, nitrate of soda, and the nitrogen of steamed bone have all 
 produced good growth. It will be noted that plot number 2, 
 receiving the standard mixture, stands at the head of the list. 
 As stated elsewhere, this standard mixture consisted of sulphate 
 of ammonia, acid phosphate, and high grade sulphate of potash. 
 This mixture was applied at the rate of 2 pounds per tree three 
 times per year. The amount was increased as the trees increased 
 in size, the application finally being at the rate of 6 pounds three 
 times per year. 
 
 Plot number 1, receiving one-half the standard amount, or 
 at the beginning 1 pound per tree three times per year, shows 
 practically the same increase in growth as plot 2. Plot number 
 3, receiving twice the standard amount, or 4 pounds per tree at 
 the beginning ranks twenty-fifth, while plot number 4, receiving 
 four times the standard amount or 8 pounds per tree, ranks at 
 the foot, having made less growth than any of the plots. The 
 standing of this series of four plots brings out the fact that in 
 this experiment plot number 1 was receiving about the optimum 
 amount of fertilizer which it would pay to apply to trees of 
 this age, and that plot number 2 received the maximum amount 
 which could be applied without inducing injury. The fact that 
 plots 2 and 1 made practically the same amount of growth indi- 
 cates that the former was receiving more fertilizer than the 
 trees could profitably use, altho not enough to injure them in 
 any way. The appearance of these two plots was very similar, 
 the eye not being able to detect any difference in size, character 
 of growth, or appearance of the leaves. Plot number 3, receiving 
 twice the standard amount of fertilizer has developed consider- 
 able injury. This injury was shown soon after the beginning of 
 the experiment, was quite severe for several years, but finally 
 became much less apparent. This would indicate that 4 pounds 
 per tree three times per year was about the maximum amount of 
 fertilizer which could be applied to young trees and not kill them 
 outright. The injury was severe during the first few years but 
 the trees managed to survive and finally to overcome the inju- 
 rious effects. The behavior of this plot in thus overcoming the 
 injurious effects of too much fertilizer is shown in Table 10. It 
 will be noted that in 1911 and 1912 this plot ranked number forty 
 in the list. In 1913 and 1914 it rose to thirty-eighth; in 1915 to 
 thirty-seventh; in 1916 and 1917 to thirty-first; and in 1918 
 to twenty-fifth. This rise in rank indicates that as the trees 
 became older they were better able to withstand the effects pro-
 
 24 Florida Agricultural Experiment Station 
 
 duced by too much fertilizer. The early injury, however, re- 
 sulted in a permanent stunting of the trees. At the end of the 
 experiment they were about three-fourths as large as the trees 
 of plots 1 and 2. 
 
 Plot 4 shows the maximum injury from the use of too much 
 fertilizer. These trees were stunted from the beginning and have 
 made very little growth. By the winter of 1912 half of the 
 trees in this plot were dead and had to be replaced by others. 
 In the spring of 1913 the excessive applications were discon- 
 tinued and from that time on only one pound per tree was used 
 three times per year. The new trees used to replace those killed 
 by the fertilizer have failed to make much growth. At the end 
 of the experiment this plot was less than one-fourth the size 
 of plots 1 and 2 and consisted of almost worthless trees which 
 will probably never amount to much. Photographs of plots 2, 
 3 and 4 are reproduced in Fig. 4. 
 
 The behavior of plots number 5, 6 and 7 is interesting in this 
 connection, because of its bearing on the question as to which 
 of the fertilizing elements used was chiefly responsible for the 
 injury produced. In this series of three plots two of the elements 
 were increased by one-half, the third being used in the standard 
 amount. In the mixture applied to plot 6 the acid phosphate and 
 high grade sulphate of potash used was one and one-half times 
 the amount used in the standard mixture, the sulphate of am- 
 monia remaining the same as in the latter. Plot 7 received H/s 
 times the nitrogen and potash of the standard and plot 5 
 received l 1 /^ times the nitrogen and phosphoric acid of the 
 standard. It will be noted that the least amount of growth was 
 made by plot 5 which ranks forty-seventh in the list. This plot 
 showed all the signs of severe injury caused by too much ferti- 
 lizer. In the table showing the rank of the plots by years plot 
 5 stood forty-first in 1911 and dropped still lower from year to 
 year, until for the last three years it stood next to the lowest. 
 
 Plot 7, where the nitrogen and potash were increased, has 
 made a better growth than plot 5 but not as much as plot 6. 
 The latter plot shows no injury from the increased phosphoric 
 acid and potash used. The trees in plot 7 show some injury 
 caused by too much fertilizer but the injury is not quite so 
 marked as in plot 5. The behavior of these three plots brings 
 out the fact that excessive quantities of nitrogen are much more 
 injurious than similar quantities of phosphoric acid and potatsh 
 and that increased ratios of nitrogen and potash are less inju-
 
 ?S*' 
 
 ifcd 
 
 Fig. 4.- 
 
 -Plots 2, :? and 4 show the effect on the orange trees when 
 
 too much fertilizer is used 
 Plot 2 was fertilized with the standard mixture. Plot :< received t 
 this amount and. from the smaller size of the trees shows that some injury 
 was caused. Plot 4 received four times the standard mixture and consi 
 largely of new trees, the original trees being practically killed by the 
 excessive quantities of fertilizer used. Plot '2 is the best plot of the forty- 
 eight; plot 3 ranked twenty-fifth, and plot 4 forty-eighth.
 
 26 
 
 Florida Agricultural Experiment Station 
 
 . 
 
 Fig. 5. Results of plots when two elements in the standard mixture 
 
 were increased.
 
 Bulletin 154, Citrus Fertilizer Experiments 27 
 
 rious than similar increases of nitrogen and phosphoric acid. 
 See Fig. 5 for photographs of these plots. 
 
 The mulched plots and the plots which received clean culti- 
 vation the entire year are among the best in the grove. This 
 treatment has been of benefit in two ways : by conserving mois- 
 ture and supplying additional nitrogen. The cultivation thru 
 the year has led to increased nitrification of the organic matter 
 of the soil thus liberating a supply of available nitrogen in 
 addition to that supplied in the fertilizer. Determinations on 
 several occasions during the early years of the experiment have 
 shown that these plots contained more nitrates in the soil than 
 was found in the soil of adjacent plots. The soil on which the 
 plots were located was naturally a rather dry soil so that the 
 continuous cultivation and the mulch of dry leaves and weeds 
 have aided in conserving moisture during dry periods. Table 
 10 shows that the clean culture plots made more growth than 
 any others during the early years of the experiment but that 
 after 1913 they did not do quite so well. This would indicate 
 that for young trees continuous clean cultivation is of benefit in 
 promoting good vigorous growth, but after a few years it is 
 possible to cultivate too much. Determinations made at the 
 end of the experiment show that the soil of the clean culture 
 plots has lost about 18 percent of the organic matter due to the 
 continuous cultivation as compared with the soil of adjacent 
 plots. (See Fig. 6 for photograph of plot 46.) 
 
 SOURCES OF NITROGEN 
 
 Sulphate of ammonia and nitrate of soda are the most com- 
 monly used sources of nitrogen for citrus trees. They are usually 
 the least expensive per pound of nitrogen and as a rule have 
 given the best results in practice. It has been pointed out else- 
 where that the continued use of sulphate of ammonia increases 
 the acidity of the soil while nitrate of soda decreases acidity, 
 and this opposite tendency of the two materials has been pre- 
 sented as an argument for using them together or alternating 
 one with the other. Additional important reasons for thus 
 using them can be given. In the discussion on soil tanks it was 
 pointed out that the loss of nitrate of soda by leaching was much 
 greater than sulphate of ammonia, and that the losses wore 
 greatest after heavy rains. In order to get the maximum benefit 
 from the use of nitrate of soda it should be used in small appli- 
 cations during the drier season of the year. Its nitrogen being
 
 Fig. 6. Plot 43, no fertilizer; Plot 32, dissolved bone black; 
 
 Plot 46, standard and clean culture 
 
 Plot 43 received no fertilizer during the period of the experiment. It 
 ranks forty-third. On plot 32 dissolved bone black was used instead of 
 acid phosphate. This plot ranked twenty-eighth. Plot 46 was fertilized 
 with the standard mixture, and in addition was cultivated thru the entire 
 year. It ranked sixth at the end of the experiment.
 
 Bulletin 154, Citrus Fertilizer Experiments 
 
 29 
 
 Fig. 7. This figure shows effects of excessive amounts of fertilizer
 
 30 Florida Agricultural Experiment Station 
 
 immediately available to the tree it is an excellent material to 
 use in the spring application of fertilizers. At this time the 
 tree is preparing to put out the spring growth and produce bloom 
 and more nitrogen is needed at this time than during any other 
 period of the year. Nitrate of soda supplies this need in a form 
 which the trees can use as soon as it is placed in the soil. Later 
 on in the season if the trees have a yellow color and show lack 
 of nitrogen a light top dressing of nitrate of soda will usually 
 be of considerable benefit, not only in putting the trees into 
 healthy growing condition but in assisting in the development 
 of the fruit. The only disadvantage likely to occur in using 
 nitrate of soda in this way comes when it is applied to a very 
 dry soil. It may remain unused in the soil for some time, until 
 a rain occurs, making it at once available, and the trees absorb 
 so much of it that injury results. This is not likely to happen if 
 small amounts are used. From 2 to 3 pounds of nitrate of 
 soda to trees bearing ten boxes of fruit may be considered a 
 rather light application. 
 
 Sulphate of ammonia may be expected to be of greater benefit 
 during the wet season. It has been shown that this material is 
 much less liable to be leached out of the soil than nitrate of soda. 
 Therefore, during the rainy season its effects will be more lasting 
 and extend over a longer period than nitrate of soda. In other 
 words, it will furnish a more constant and uniform supply of 
 nitrogen during the wet period. The ammonia of this material 
 becomes available to the plant only after it has been changed 
 to the nitrate form thru the process of nitrification. This change 
 is brought about gradually and thus the effects of the sulphate 
 of ammonia are extended over a longer period. It will be noted 
 in Table 9 that plot 16 which received one-half of the nitrogen 
 in the form of sulphate of ammonia and the other half as nitrate 
 of soda made a better growth than any plot receiving nitrate of 
 soda exclusively, thus emphasizing the point brought out that 
 the two materials used together will give better results than 
 where nitrate of soda is used alone. 
 
 ORGANIC SOURCES OF NITROGEN 
 
 Two plots, 25 and 26, received steamed bone as the source of 
 phosphoric acid and as this material carried a little over 3 
 percent ammonia this was taken into account. As the quantity 
 of steamed bone required to supply the proper amount of phos- 
 phoric acid furnished less than one-fourth enough nitrogen the 
 balance was made up of sulphate of ammonia, so that the main
 
 Bulletin 154, Citrus Fertilizer Experiments 31 
 
 source of nitrogen for these trees was the latter material. The 
 behavior of steamed bone as a source of phosphoric acid is 
 discussed in the section on Sources of Phosphoric Acid. 
 
 With one or two exceptions the plots receiving dried blood or 
 cottonseed meal are not among the best. Plot 47, one of the 
 best in the experiment, received clean cultivation in connection 
 with dried blood, during the entire period. It has already been 
 pointed out that this cultivation was of marked benefit in pro- 
 ducing growth, especially during the early years of the experi- 
 ment. On plot 22 cottonseed meal was used in connection with 
 sulphate of ammonia, the amount of the latter being the same 
 as was used on plot 1 which ranked second in the series. While 
 these materials have not brought about any actual injury and, 
 contrary to the general opinion, have not produced dieback, this 
 experiment has shown that they should not be relied upon as the 
 sole source of nitrogen for citrus trees. Experience has shown 
 that an occasional application of one or the other may be of 
 benefit probably in stimulating the growth of the beneficial soil 
 bacteria, but when used continuously they are distinctly inferior 
 to the mineral sources of nitrogen. 
 
 SOURCES OF PHOSPHORIC ACID 
 
 Of the five sources of phosphoric acid used, acid phosphate 
 has given the best results. The eleven best plots all received 
 this material. Steamed bone has also given good results, plot 
 25, which received this material, ranking twelfth in the list. 
 No explanation can be given for the poor behavior of dissolved 
 bone black in this experiment. As Table 10 shows, neither of 
 the two plots, 24 and 32, fertilized with this material, have ever 
 ranked above twenty-third during the ten 1 years of the experi- 
 ment. The same thing may be said with regard to plots 27 and 
 28, fertilized with Thomas slag. These two plots have stood 
 near the bottom of the list during the ten years' work. The trees 
 in both these plots have shown evidence of malnutrition, such 
 as frenching, and in some years have produced but a small 
 amount of new growth. Plot 28, receiving twice as much 
 Thomas slag as plot 27, consists on the average of somewhat 
 smaller trees, showed more frenching from time to time, and in 
 general showed more pronounced symptoms of poor nutrition 
 during the period of the experiment than did plot 27. 
 
 I'SK OF FLOATS 
 
 Plots 33, 34, 35 and 3(> wore fertilized with finely ground raw 
 rock phosphate, commonly known as floats. The formulas used
 
 32 Florida Agricultural Experiment Station 
 
 were as follows: Plot 33, 5-6-6, from sulphate of ammonia, 
 floats and high grade sulphate of potash; plot 34, 5-12-6, from 
 the same materials; plot 35, 5-24-6, from the same materials; 
 plot 36, 5-24-6, from cottonseed meal, floats and high grade sul- 
 phate of potash. 
 
 At the end of the experiment plots 35 and 36 were receiving 
 a quantity of floats equivalent to a yearly application of over 
 1300 pounds per acre. It will be noted that these two plots made 
 the best growth among the float plots. In 1912 they ranked 
 third and seventh respectively. From 1913 on they gradually 
 declined as compared with other plots, until at the end of the 
 experiment in 1918 they were in the nineteenth and eighteenth 
 places. Plot 36 made somewhat more growth on the average 
 than plot 35. The rank of plot 36 from year to year is shown 
 graphically in Fig. 8. It will be noted that plot 36 was at its 
 best in 1913, and that from that year on there was a gradual 
 decline in comparative growth. This decline may probably be 
 attributed to the inability of the trees to obtain sufficient phos- 
 phoric acid from the floats to make maximum growth. However, 
 both 35 and 36 were among the best half of the plots at the 
 end of 1918. 
 
 AVAILABILITY OF PHOSPHATES 
 
 The better results obtained by the use of acid phosphate over 
 other sources of phosphoric acid, should in all probability be 
 attributed to its more ready availability. A large proportion of 
 the phosphoric acid which it carries is soluble in water, while 
 such materials as bone, Thomas slag and floats contain no water- 
 soluble phosphoric acid. So far as known the phosphoric acid 
 of the soil is absorbed by the plant roots in only one form, namely, 
 the mono-calcium phosphate, or the so-called water-soluble form 
 found in acid phosphate. This form contains one part of lime 
 combined with two parts of phosphoric acid. When acid phos- 
 phate is added to the soil the mono-calcium phosphate combines 
 with more lime to form the di-calcium phosphate, or the so- 
 called "reverted" phosphate, which contains two parts of lime 
 combined with two parts of phosphoric acid. The reverted form 
 is fairly soluble in water containing carbon dioxide. Usually 
 an additional change takes place later on and the reverted form 
 combines with still more of the lime of the soil and forms tri- 
 calcium phosphate, containing three parts of lime combined with 
 two of phosphoric acid. This is the form of phosphoric acid 
 found in floats and bone.
 
 Bulletin 154, Citrus Fertilizer Experiments 
 
 33 
 
 19/0 
 
 iff. 8. Comparative jrrowth of plots 27, 4-'?, .'?!', 3<> and !('
 
 34 Florida Agricultural Experiment Station 
 
 The thought might occur that since acid phosphate after 
 being added to the soil ultimately assumes the form of the tri- 
 calcium phosphate, it would be reasonable to expect as good 
 results from a direct application of the latter form of material. 
 The difference in availability is explained by the fact that when 
 acid phosphate is added to the soil it dissolves in the soil water 
 and is soon distributed uniformly and widely among the soil 
 particles. When it changes to the reverted form it remains as 
 a thin film deposited over the surface of the particles of soil and 
 thus is in the best possible condition to go into solution thru the 
 action of the soil water and to come into contact with the tree 
 roots. 
 
 Where the insoluble phosphates are used it is impossible to 
 obtain as thoro and uniform a distribution of the solid particles 
 of the material, even if very finely powdered, as it is in the case 
 of a solution. 
 
 The phosphoric acid of steamed bone, altho in the form of 
 tri-calcium phosphate, is more readily available than the same 
 form as contained in floats. In the former material the phos- 
 phoric acid is intimately associated with the organic material 
 of the bone. When this decays it acts on the insoluble phosphate 
 and makes it gradually available. Steamed bone has usually 
 given excellent results as a source both of nitrogen and of phos- 
 phoric acid, and while not as quick acting as some other mate- 
 rials, its effects are usually more lasting. It is usually considered 
 that about one-half of the phosphoric acid of steamed bone be- 
 comes available the first season, the remainder gradually be- 
 coming available in succeeding years. 
 
 SOURCES OF POTASH 
 
 Of the six sources of potash used in this experiment, the high 
 grade and low grade sulphates and hard wood ashes have all given 
 excellent results. The best ten plots all received high grade 
 sulphate of potash. Plot 37 to which low grade sulphate of 
 potash was applied, ranked eleventh at the end of the work. 
 The hard wood ashes plot ranked fifteenth. One objection to 
 the continuous use of the latter material has been brought out 
 in this experiment, and is discussed in the section dealing with 
 lime and other alkaline materials. The frenched condition of the 
 trees brought on by the ashes was not so severe as on other plots, 
 but was sufficient to interfere somewhat with normal growth. 
 An occasional application of ashes to citrus trees would probably
 
 Bulletin 154, Citrus Fertilizer Experiments 35 
 
 give very little if any trouble. The muriate and the nitrate of 
 potash gave only fair results. The trees on these two plots did 
 not produce quite the thrifty, vigorous growth characteristic of 
 the best plots. 
 
 The trees in plot 40, which received kainit as the source of 
 potash, made very poor growth during the entire period of the 
 experiment. Compared with plots receiving the high and low 
 grade sulphate and ashes, they were smaller in size, growth was 
 less abundant, and appeared much less thrifty and vigorous. 
 This plot received the same treatment as plot 41 in the next row, 
 excepting the source of potash, but the trees were not more 
 than two-thirds the size of those in plot 41. 
 
 SOIL ACIDITY 
 
 Table 11 gives the lime requirement of the various plots for 
 four different dates, samples of soil being taken in March, July, 
 and December of 1913 and in July, 1915. By the term "lime 
 requirement" is meant the amount of lime necessary to be added 
 to the soil to bring about an alkaline reaction. In the method used 
 the soil is treated with varying quantities of lime water of 
 standard strength until the proper amount necessary to give an 
 alkaline reaction is reached. The figures in the table represent 
 pounds of calcium carbonate (ground limestone) per acre. 
 Samples of soil were taken from the plots where the fertilizers 
 had been applied and also in the middle of the tree rows where 
 the soil had never been fertilized. The difference between the 
 lime requirement of any plot and the corresponding middle would 
 show the effect of the fertilizer used on the plot in increasing or 
 decreasing the acidity of the soil. It will be noted from the 
 table that plots 11, 12, 21 and 39, receiving ground limestone, 
 and plot 30, receiving hardwood ashes, all show an alkaline 
 reaction, due to the effect of these basic materials in neutralizing 
 the acidity originally present and also that which may have de- 
 veloped from time to time. Plots 27 and 28, receiving basic slag 
 and nitrate of soda, show a marked decrease in lime require- 
 ment as compared with the corresponding checks. Basic slag 
 has an alkaline reaction and contains usually a small excess of 
 lime over and above that in combination with the phosphoric 
 acid in it. This excess of lime is seldom over 5 to 10 percent. 
 Hence, basic slag in the amounts ordinarily applied in practice 
 would not supply sufficient lime to neutralize the acid condition 
 of a sour soil except in a limited degree as is here shown. The
 
 36 
 
 Florida Agricultural Experiment Station 
 
 TABLE 11. LIME REQUIREMENT. POUNDS PER ACRE, 9 INCHES 
 
 Plot No. 
 
 March 
 ~Plot 
 
 , 1913 
 Middle 
 
 July, 
 Plot 
 
 1913 
 
 Middle 
 
 Dec., 
 Plot 
 
 1913 
 Middle 
 
 July, 
 Plot 
 
 1915 
 Middle 
 
 1 
 
 1600 
 
 1070 
 
 2140 
 
 1070 
 
 1600 
 
 1070 
 
 2140 
 
 2140 
 
 2 
 
 2670 
 
 1600 
 
 3210 
 
 2670 
 
 3210 
 
 1600 
 
 3740 
 
 2670 
 
 3 
 
 2670 
 
 1070 
 
 3210 
 
 2670 
 
 3210 
 
 2140 
 
 4810 
 
 2140 
 
 4 
 
 3210 
 
 1070 
 
 3740 
 
 2140 
 
 2670 
 
 2140 
 
 4810 
 
 1600 
 
 5 
 
 2670 
 
 1070 
 
 3740 
 
 2140 
 
 3740 
 
 2140 
 
 5350 
 
 1600 
 
 6 
 
 4280 
 
 1070 
 
 3740 
 
 2670 
 
 3740 
 
 2140 
 
 4810 
 
 2140 
 
 7 
 
 2670 
 
 1600 
 
 3740 
 
 2670 
 
 3210 
 
 1600 
 
 3740 
 
 2670 
 
 8 
 
 2670 
 
 1070 
 
 3210 
 
 1070 
 
 2140 
 
 1070 
 
 3740 
 
 2140 
 
 9 
 
 2670 
 
 1070 
 
 3210 
 
 2140 
 
 2140 
 
 1600 
 
 2670 
 
 1600 
 
 10 
 
 2870 
 
 2140 
 
 3210 
 
 2670 
 
 3210 
 
 2140 
 
 3210 
 
 3210 
 
 11 
 
 Alk.* 
 
 2670 
 
 Alk.* 
 
 3210 
 
 Alk.* 
 
 3210 
 
 Alk.* 
 
 2670 
 
 12 
 
 Alk.* 
 
 2670 
 
 . Alk.* 
 
 3210 
 
 Alk.* 
 
 3210 
 
 Alk.* 
 
 4280 
 
 13 
 
 3740 
 
 2670 
 
 4280 
 
 3210 
 
 4280 
 
 3210 
 
 4810 
 
 4280 
 
 14 
 
 2670 
 
 2670 
 
 3740 
 
 3210 
 
 3740 
 
 3210 
 
 4810 
 
 2670 
 
 15 
 
 2670 
 
 2140 
 
 3740 
 
 2670 
 
 2670 
 
 2140 
 
 2670 
 
 3210 
 
 16 
 
 2670 
 
 1070 
 
 2140 
 
 2140 
 
 2670 
 
 1600 
 
 3740 
 
 1600 
 
 17 
 
 2670 
 
 2670 
 
 3210 
 
 3210 
 
 3210 
 
 2670 
 
 4810 
 
 3210 
 
 18 
 
 2670 
 
 2670 
 
 3740 
 
 4810 
 
 2670 
 
 2670 
 
 4280 
 
 2670 
 
 19 
 
 2670 
 
 2140 
 
 4280 
 
 3210 
 
 2140 
 
 2670 
 
 4280 
 
 3740 
 
 20 
 
 2670 
 
 2670 
 
 3740 
 
 4280 
 
 2670 
 
 2670 
 
 3740 
 
 3210 
 
 21 
 
 Alk.* 
 
 2670 
 
 Alk.* 
 
 4280 
 
 Alk.* 
 
 2670 
 
 Alk.* 
 
 3210 
 
 22 
 
 2670 
 
 2140 
 
 5350 
 
 3210 
 
 4280 
 
 2670 
 
 4280 
 
 3740 
 
 23 
 
 2670 
 
 2670 
 
 4810 
 
 4810 
 
 2670 
 
 2670 
 
 5350 
 
 2670 
 
 24 
 
 2670 
 
 2670 
 
 5890 
 
 3210 
 
 3740 
 
 2670 
 
 4280 
 
 3210 
 
 25 
 
 2670 
 
 2670 
 
 3740 
 
 3740 
 
 2670 
 
 2670 
 
 3210 
 
 3210 
 
 26 
 
 2140 
 
 2670 
 
 4810 
 
 2670 
 
 3210 
 
 2670 
 
 3210 
 
 2670 
 
 27 
 
 1600 
 
 2140 
 
 2140 
 
 3740 
 
 2140 
 
 2140 
 
 1600 
 
 2140 
 
 28 
 
 1070 
 
 2670 
 
 3210 
 
 3740 
 
 1070 
 
 2670 
 
 2140 
 
 5350 
 
 29 
 
 2670 
 
 2670 
 
 4810 
 
 3740 
 
 4280 
 
 2670 
 
 4810 
 
 5350 
 
 30 
 
 Alk.* 
 
 2140 
 
 Alk.* 
 
 3740 
 
 Alk.* 
 
 2140 
 
 Alk.* 
 
 2140 
 
 31 
 
 3210 
 
 2670 
 
 4810 
 
 2670 
 
 3210 
 
 2670 
 
 4810 
 
 2670 
 
 32 
 
 3210 
 
 2670 
 
 4810 
 
 3740 
 
 3210 
 
 2670 
 
 4280 
 
 3210 
 
 33 
 
 2140 
 
 3210 
 
 3740 
 
 2670 
 
 2670 
 
 2140 
 
 3740 
 
 3210 
 
 34 
 
 2140 
 
 2140 
 
 4280 
 
 3210 
 
 2670 
 
 2670 
 
 3740 
 
 3210 
 
 35 
 
 2140 
 
 2670 
 
 4280 
 
 3210 
 
 3740 
 
 2670 
 
 5350 
 
 3740 
 
 36 
 
 2670 
 
 2140 
 
 4280 
 
 4280 
 
 3210 
 
 2140 
 
 3740 
 
 2670 
 
 37 
 
 3740 
 
 2140 
 
 4810 
 
 4280 
 
 2670 
 
 2140 
 
 5350 
 
 2670 
 
 38 
 
 3210 
 
 2670 
 
 4280 
 
 3210 
 
 3740 
 
 2670 
 
 4280 
 
 3740 
 
 39 
 
 Alk.* 
 
 2140 
 
 Alk.* 
 
 3210 
 
 Alk.* 
 
 2670 
 
 Alk.* 
 
 3210 
 
 40 
 
 3210 
 
 3210 
 
 4810 
 
 2670 
 
 2670 
 
 2140 
 
 3740 
 
 3210 
 
 41 
 
 2670 
 
 2140 
 
 3740 
 
 2670 
 
 2670 
 
 1600 
 
 3740 
 
 2670 
 
 42 
 
 2140 
 
 2140 
 
 3740 
 
 2140 
 
 2140 
 
 1600 
 
 2670 
 
 2140 
 
 43 
 
 2140 
 
 2670 
 
 3740 
 
 2670 
 
 2140 
 
 2140 
 
 3210 
 
 4280 
 
 44 
 
 4280 
 
 2140 
 
 5350 
 
 6420 
 
 3740 
 
 3740 
 
 5350 
 
 4280 
 
 45 
 
 4280 
 
 2140 
 
 7490 
 
 6420 
 
 5890 
 
 3740 
 
 6960 
 
 4280 
 
 46 
 
 3210 
 
 2670 
 
 4280 
 
 2670 
 
 3740 
 
 2140 
 
 3740 
 
 4280 
 
 47 
 
 2670 
 
 2140 
 
 3740 
 
 2140 
 
 3210 
 
 1600 
 
 2670 
 
 2140 
 
 48 
 
 2140 
 
 2140 
 
 3210 
 
 2670 
 
 2140 
 
 1600 
 
 3210 
 
 2670 
 
 *Alkaline. 
 
 neutralizing effect shown in these two plots is also influenced 
 by the nitrate of soda used in connection with the basic slag. 
 Nitrate of soda also has an alkaline reaction in the soil due to 
 the fact that the NO3 or nitrate part of the material is used 
 up by the tree much faster than the NA or sodium portion.
 
 Bulletin 154, Citrus Fertilizer Experiments 37 
 
 This leads to more or less of an accumulation in the soil of the 
 sodium element, which by combining with the carbonic acid 
 gas of the soil water forms carbonate of soda, a material having 
 an alkaline reaction. 
 
 The effect of nitrate of soda on an acid soil is also brought 
 out by a study of the lime requirement of plots 15 and 48 which 
 received this material as the source of nitrogen. In both plots 
 the tendency of the nitrate of soda to decrease acidity is clearly 
 shown. In plot 15 there is an actual decrease in the acid condi- 
 tion of the soil, while in plot 48 the soda has at least prevented an 
 increase. In the soil of plot 42, receiving nitrate of potash and 
 nitrate of soda, the tendency also is for the acidity to decrease. 
 
 ACID FERTILIZERS 
 
 The well known tendency of sulphate of ammonia to increase 
 the acid condition of the soil is shown here in the majority of 
 the plots receiving this material as the source of nitrogen. The 
 plots showing the highest degree of acidity nearly all receive 
 this material. It is true that some form of phosphoric acid and 
 of potash were used on each plot in connection with the sulphate 
 of ammonia and it might be argued that these materials were in 
 part responsible for the acid condition present. The work of 
 other investigators, however, where sulphate of ammonia was 
 used alone, has shown that this material must be held as the 
 chief cause of acidity. The absorption and nitrification of the 
 ammonia of this material is comparatively rapid, being followed 
 by its final utilization by the tree. This leaves the sulphuric acid 
 portion in the soil, thus bringing about acid conditions. The 
 potash of the muriate and sulphate of potash disappears much 
 more slowly from the soil as the latter has ;the power of retaining 
 for some considerable time the potash or basic element of these 
 materials. Therefore, while the tendency of these materials 
 would be to produce in the long run an acid condition, their action 
 would be much slower than sulphate of ammonia. Similarly, it 
 has been shown that the continuous use of acid phosphate does 
 not increase acidity. On the contrary, it seems to decrease some- 
 what the acidity already present in the soil. The figures in 
 Table 11 for the plots receiving floats or raw rock phosphate 
 are not very conclusive. In three plots out of four sulphate of 
 ammonia was used with the floats so that the influence of the 
 latter on the acidity of the soil would be over-shadowed by that 
 of the sulphate of ammonia. In general, however, it may be said 
 that the use of floats would have a tendency to decrease the 
 
 210J85
 
 38 Florida Agricultural Experiment Station 
 
 acidity of the soil. The various forms of raw rock phosphate 
 on the market contain more or less carbonate of lime as an 
 impurity and their influence on the acid condition of the soil 
 would be proportional to the amount of this material present. 
 
 EFFECT OF ACIDITY ON GROWTH 
 
 So far as could be noted an acid soil has no injurious effect 
 on the growth of the orange tree. On some of the most acid 
 plots in the grove the trees are vigorous and have made very good 
 growth ranking well up among the best plots in the grove. These 
 experiments would seem to show that so far as growth is con- 
 cerned the citrus tree is very little influenced by an acid condition 
 of the soil. Where a leguminous cover crop is desired during the 
 rainy season the situation is different. During the early years of 
 the experiment a beggarweed cover crop was allowed to occupy 
 the soil during the summer months. After a time the soil became 
 so acid that a fair stand could not be obtained and cowpeas and 
 velvet beans were used instead. These crops appear to be much 
 less susceptible to acidity than beggarweed and will do fairly 
 well on soils on which the beggarweed almost refuses to grow. 
 A study of Table 11 brings out the interesting fact that the 
 acidity varies with the season, being greater in summer than in 
 winter. The average number of pounds per acre of carbonate of 
 lime required for the plots receiving the standard mixture of 
 sulphate of ammonia, acid phosphate and high grade sulphate of 
 potash is 4360 for the summer months and 3050 for the winter 
 months, a difference of over half a ton. A probable explanation 
 of this fact is that during the summer months the high tem- 
 peratures and abundant rainfall lead to more rapid chemical and 
 biological changes in the soil. This brings about greater decay 
 of organic matter and more rapid transformations in the fertiliz- 
 ing materials present, resulting in a more rapid formation of 
 acids. 
 
 NATURE OF SOIL ACIDITY 
 
 Soils may become acid or sour (1) thru an accumulation of 
 organic acids produced in the decay of vegetable matter; (2) 
 thru the depletion of the alkaline or basic constituents of the 
 soil; (3) thru the addition of fertilizers leaving an acid residue 
 in the soil. Most muck and peat soils are acid in character before 
 being brought into cultivation. This is also true of many virgin 
 soils of a more sandy nature. The decay of the vegetable matter 
 present in such soils leads to the formation of organic acids, 
 which tend to accumulate, especially if these soils are naturally
 
 Bulletin 154, Citrus Fertilizer Experiments 39 
 
 deficient in lime or if they are ill drained. After such soils are 
 cleared, drained and brought under cultivation this acid condi- 
 tion disappears to a considerable extent, due to the aeration or 
 introduction of oxygen into the soil thru cultural treatment. 
 Where a crop of green material is turned under, as in the prac- 
 tice of green manuring, the soil may become acid for a time 
 due to the formation of organic acids in the decay of the vege- 
 table matter plowed under. In any case where acids are formed 
 they lead to a depletion of the lime of the soil. It might be said 
 that all soils tend to become acid in time due to the removal of 
 lime and other basic materials in the drainage water. Both the 
 lime in carbonate of lime and that in certain silicate compounds 
 present in soils are dissolved by the soil acids and are leached 
 out. When these forms of lime finally disappear from the soil an 
 acid condition, so far as plant growth is concerned, is produced. 
 An application of lime in some form is required to bring back 
 the alkaline reaction. Florida high pine and flat woods soils, 
 as a general rule, contain relatively small quantities of lime 
 (usually very little if any in the carbonate form), yet the amount 
 of this material appearing in the drainage water is surprising. 
 In experiments carried out by the Florida Experiment Station 
 it has been found that in the course of 10 months lime equivalent 
 to 250 pounds of calcium carbonate has leached out and appeared 
 in the drainage water from an acre of land. Such a loss of lime 
 if continued for a few years would bring about acid conditions 
 in the soil. 
 
 The use of fertilizers such as sulphate of ammonia, which 
 leave an acid residue in the soil, is a frequent cause of soil 
 acidity under Florida conditions. The acid residue combines 
 with the lime of the soil and changes it to a soluble form which 
 readily leaches out. In studying the loss of lime where different 
 sources of ammonia were applied to the soil, the Experiment 
 Station has found that where sulphate of ammonia was used 
 the loss was over two times as much as where nitrate of soda 
 was used. This tendency of nitrate of soda to decrease acidity, 
 in other words, to conserve the lime of the soil, has already been 
 mentioned in connection with the discussion of the loss of ferti- 
 lizers by leaching. 
 
 An important feature in the use of these two materials is 
 thus brought out. It is an advantage to use them together or 
 alternately, as, for example, nitrate of soda as the source of 
 ammonia in the spring and sulphate of ammonia in the summer.
 
 
 Fig. 9. Phosphate plots 
 
 Plots 27 and 28 were fertilized with Thomas slag instead of acid phos- 
 phate. The source of nitrogen was nitrate of soda. Plot 28 received twice 
 as much slag as plot 27. The trees in both these plots showed considerable 
 frenching, plot 28 being much more severely affected. Most of the trees 
 in plot 28 show the type of growth usually characteristic of badly frenched 
 trees. Plot 36 received its phosphoric acid in the form of floats, four times 
 the standard amount or 24 percent being used in the mixture. At the end of 
 the experiment this plot ranked eighteenth. Plot 27 ranked thirty-fifth and 
 plot 28 ranked fortv-fourth.
 
 Bulletin 154, Citrus Fertilizer Experiments 41 
 
 Thus the nitrate of soda would counteract the acid condition 
 brought about by the sulphate of ammonia. Other and greater 
 advantages in thus using the two materials are discussed else- 
 where. 
 
 LIME AND OTHER ALKALINE MATERIALS 
 
 Lime and other alkaline materials \ised in this experiment have 
 proven distinctly injurious to growth. This injury consisted, 
 in its .mildest form, of a light attack of frenching; in the severest 
 type, of chronic, severe frenching, partial defoliation, and 
 a permanent retarding of growth, resulting in stunted under- 
 sized and unhealthy trees. The alkaline materials and the ferti- 
 lizers used in connection with the plots were as follows: 
 
 Plot 11, 5-6-6, from sulphate of ammonia, acid phosphate, high 
 grade sulphate of potash ; ground limestone, 10 pounds per tree. 
 
 Plot 12, 5-6-6, same fertilizer treatment as plot 11, with lime- 
 stone replaced by air-slaked lime, 5 pounds per tree. 
 
 Plot 21, 5-6-6, from cottonseed meal, acid phosphate, high- 
 grade sulphate of potash ; ground limestone, 10 pounds per tree. 
 
 Plot 27, 5-6-6, from nitrate of soda, Thomas slag, high-grade 
 sulphate of potash. 
 
 Plot 28, 5-12-6, from same materials as plot 27. 
 
 Plot 30, 5-6-6, from nitrate of soda, acid phosphate, hard wood 
 ashes. 
 
 Plot 39, 5-6-6, same treatment as plot 11. 
 
 The ground limestone and air-slaked lime were applied in the 
 spring about two months after the spring application of ferti- 
 lizers, and were distributed about the tree to about the same 
 distance from the trunk as the fertilizers. The slag and hard- 
 wood ashes were applied mixed with the other fertilizers. The 
 limestone and air-slaked lime were applied every year, beginning 
 with 1909, until 1913, when the injury produced became quite 
 noticeable and their use was discontinued for the remainder of 
 the period of the experiment. The slag and ashes were used 
 during the entire ten years. 
 
 During the early years of the experiment considerable french- 
 ing was found in all parts of the grove. As the trees suffered 
 from dieback during these years the frenching was attributed to 
 the same causes which produced the former disease. In 1913 it 
 was noticed that the trees on some of the plots receiving alkaline 
 materials were more severely fronched than the remainder of 
 the grove. The worst injury was found on the ground limestone
 
 
 
 Fig. 10. Plots 11, 12 and 21, on which lime was used 
 The plots illustrated here were treated with lime in addition to the 
 fertiliser. Plot 11 received the standard fertilizer mixture and ground 
 limestone. Plot 21 received the standard mixture with the sulphate of am- 
 monia replaced by cottonseed meal and ground limestone in addition. This 
 plot showed much more frenching than plot 11. Plot 12 was fertilized with 
 the standard mixture and air-slaked lime in addition. The trees showed 
 very little frenching.
 
 Bulletin 154, Citrus Fertilizer Experiments 43 
 
 plots and on the plot receiving a double quantity of slag. The 
 trees on the air-slaked lime plot and on the ashes plot also showed 
 considerable frenching, which, however, almost completely dis- 
 appeared after 1915, while the trees on the limestone and slag 
 plots developed the more severe symptoms of the disease, such as 
 the narrow pointed leaves, partial defoliation, and general un- 
 thrifty appearance. The disease continued to manifest itself 
 in this aggravated form in these particular plots, until the clos- 
 ing out of the experiment. It seriously interfered with normal 
 growth, the trees on the most severely affected plots appearing 
 stunted, undersized and unhealthy. 
 
 Photographs of plots 11, 12, 21, 27 and 28 are reproduced in 
 Figs. 9 and 10. 
 
 For a more detailed discussion of the injury induced by ground 
 limestone, the reader is referred to Fla. Exp. Sta. Bulletin No. 
 137, Injury to Citrus Trees by Ground Limestone, by B. F. Floyd. 
 
 DIEBACK IN THE GROVE 
 
 In July, 1910, eighteen months after they had been set out, 
 it was noticed that many of the trees exhibited the early stages 
 of the disease known as dieback. At this time the symptoms 
 were mainly the presence of gum pockets and the S-shaped 
 branching. An examination showed about 78 percent of the 
 trees thus affected. At the same time the trees presented a 
 generally unhealthy appearance, much of the growth coming 
 from the lower parts of the tree and from suckers. No measures 
 for combatting the disease were adopted at this time, since it 
 was considered very undesirable to introduce such complications 
 in the experiment unless absolutely necessary. The grove was 
 thoroly examined again in March, 1911, and in the fall of that 
 year when it was evident that the disease had gained much 
 headway and was causing serious damage. Table 12 shows the 
 extent to which the grove was affected with the disease. In this 
 table the number of the plot and the fertilizer treatment is 
 given, in column I the number of trees in each plot showing 
 symptoms of dieback in July 1910; in column II those showing 
 symptoms in March 1911, and in column III those developing 
 the symptoms in the growth made in the spring of 1911. (The 
 writer is indebted to B. F. Floyd, Plant Physiologist, for this 
 table.) 
 
 RELATION OF DISEASE TO FERTILIZER 
 
 The use of organic nitrogenous fertilizers has usually been 
 regarded as a cause of dieback. A study of Table 12 however,
 
 TABLE 12. TREES AFFECTED BY DIEBACK 
 FERTILIZERS APPLIED 
 
 Different amounts I [ II 
 
 "Half" the standard." .'...: I....:. 4 
 
 Standard .... 2 
 
 Double the standard 6 
 
 Four times the standard 9 
 
 Phosphoric aci'd and ammonia increased by one-half.... 9 
 
 Phosphoric acid and potash increased by one-half 8 
 
 Ammonia and potash increased by one-half 10 
 
 Phosphoric acid and potash decreased by one-half 9 
 
 Phosphoric acid and ammonia decreased by one-half.... 9 
 
 Ammonia and potash decreased by one-half 9 
 
 Standard and finely ground limestone 7 
 
 Standard and air-slacked lime , , _. 9 
 
 Standard and mulch 7 
 
 Standard ....'. 8 
 
 Nitrogen from different sources 
 
 From nitrate of soda 1 9 9 
 
 Half from nitrate of soda, and half from sulphate of 
 
 ammonia 9 9 
 
 From dried blood 8 8 
 
 Half from sulphate of ammonia, and half from dried 
 
 blood 9 8 
 
 Half from nitrate of soda, and half from dried blood.. 7 7 
 
 From cottonseed meal 4 4 
 
 From cottonseed meal. (With ground limestone.) 6 5 
 
 Half from cottonseed meal, and half from sulphate of 
 
 ammonia 8 9 
 
 Half from cottonseed meal, and half from nitrate of 
 
 soda , 10 9^ 
 
 Phosphoric acid from different sources 
 
 From dissolved bone black 7 10 
 
 From steamed bone 10 9 
 
 From steamed bone. (Double amount.) 9 10 
 
 From Thomas' slag. (Nitrogen from nitrate of soda.).. 8 8 
 From Thomas' slag. (Double amount. Nitrogen from 
 
 nitrate of soda.) 4 6 
 
 From acid phosphate. (Potash, 7% percent in June, 
 
 TVz percent in October and 3 percent in February.) 8 7 
 From acid phosphate. (Nitrogen from nitrate of soda. 
 
 Potash from hardwood ashes.) 4 4 
 
 From acid phosphate. (Standard.) 10 10 
 
 From dissolved boneblack 8 9 
 
 From floats 10 10 
 
 From floats. (Double amount.) 9 10 
 
 From floats. (Four times amount.) 9 10 
 
 From floats. (Four times amount. Nitrogen from 
 
 cottonseed meal.) 8 10 
 
 Potash from, different sources 
 
 From low-grade sulphate 9 9 
 
 From muriate 9 8 
 
 From high-grade sulphate. (With ground limestone.) 10 10 
 
 From kainit 6 10 
 
 From high-grade sulphate. (Standard.) 7 9 
 
 From nitrate of potash. (Balance of nitrogen from 
 
 nitrate of soda.) 8 9_ 
 
 Different culture, etc. 
 
 No fertilizer 3 4 
 
 Standard 7 10 
 
 Standard and mulch 8 8 
 
 Standard and clean culture 10 10 
 
 Nitrogen from dried blood. Clean culture 9 10 
 
 Nitrogen from nitrate of soda. Clean culture 7 6 
 
 Total number of trees affected with dieback |373 1411 |241
 
 Bulletin 154, Citrus Fertilizer Experiments 45 
 
 brings out the fact that in this instance plots receiving a strictly 
 mineral fertilizer were as badly affected with the disease as 
 were those receiving cottonseed meal, dried blood and other 
 organic sources of nitrogen. At no time during the progress 
 of the disease could any definite relation be established between 
 the disease and any particular fertilizer. In other words, the 
 disease appeared to be entirely independent of the fertilizers 
 used. It has been mentioned elsewhere that when they were set 
 out three-fourths of a pound of steamed bone meal was used 
 under each tree. It is possible that the organic nitrogen in the 
 bone meal may have been the primary cause of the disease, but 
 as every tree in the grove was treated in this way this theory was 
 impossible of proof. 
 
 TREATMENT OF DIEBACK 
 
 In the spring of 1912 the disease had reached a serious stage 
 and it became evident that measures for combatting it must be 
 taken. The more advanced symptoms, such as bark excrescences, 
 stained terminal branches, and multiple buds, were quite abun- 
 dant, and a few trees were in such bad condition that it was 
 necessary to replace them with others. The fertilizer applica- 
 tions for the spring and summer of 1912 were omitted and the 
 trees were sprayed with Bordeaux mixture in February and 
 April. In order to get at the effect of this spray in controlling 
 the disease, the fifth tree in every plot was left unsprayed as a 
 check. In the latter part of the year it was evident that the 
 disease was much less prevalent than before the treatment. In 
 January, 1913, B. F. Floyd made a careful examination of the 
 
 TABLE 13. DIEBACK ON EXPERIMENTAL PLOTS IN JANUARY, 1913 
 
 3 52 
 
 5 __ O W2 22 
 
 Affected trees among 
 
 sprayed Ill 20 , 10 4 
 
 Affected trees among un- 
 sprayed .. 13 
 
 Percentage affected trees 
 
 among sprayed 25.7 
 
 Percentage affected trees 
 
 among unsprayed 56.2 31.3 27.1 2.1 2.1 
 
 Total number trees af- 
 
 4.6 2.3 0.93 
 
 fected 
 
 138 
 
 35 23
 
 46 Florida Agricultural Experiment Station 
 
 trees for symptoms of dieback. Table 13 summarizes his notes 
 made at that time. This table shows that over 56 percent of the 
 unsprayed trees still showed dieback in the gum pocket stage as 
 compared with 25.7 percent of the sprayed trees. While a total 
 of 138 trees showed this symptom, none were at all severely 
 affected or were being injured by the disease. The superficial 
 symptoms such as stained terminal branches, bark excrescences 
 and multiple buds, were quite scarce. It will be noted that in 
 November, 1911, 81.7 percent of the trees showed gum pockets, 
 while in January, 1913, the unsprayed trees showed 56.2 percent 
 affected. This indicates a decrease in the disease during this 
 period from causes other than the spray treatment. Probably 
 the omission of the fertilizer application or other natural causes 
 were of influence here in bringing about a decrease in the disease. 
 Nevertheless it may be concluded from the data given that the 
 Bordeaux treatment was quite effective in this instance in the 
 control of dieback. In June, 1913, the trees appeared to be 
 practically free from the disease, but in June, 1915, slight indi- 
 cations of it were again noted. Gum pockets were found on the 
 new growth on 52 trees. They were not numerous on any of 
 the trees, in most cases a careful search being necessary to find 
 them. Of the 52 trees affected, 28 were the fifth tree in the 
 plot, trees which had been left unsprayed at the time of treatment 
 with Bordeaux mixture. No further treatment was given at this 
 time and the symptoms of the disease disappeared from natural 
 causes later in the year. From the end of the year 1915 on to 
 the close of the experiment, no further trouble was experienced 
 with the disease. 
 
 FREEZE OF 1917 
 
 During the first week of February, 1917, a cold wave swept 
 over the state bringing freezing temperatures, especially on the 
 3rd and 4th, and causing considerable damage to the citrus and 
 truck industries. 
 
 In the experimental grove temperatures of 21 on the 3rd, and 
 22 on the 4th were noted. A reproduction of the air and soil 
 temperature records for the grove for the week ending February 
 5 is given in Fig. 11. In order to ascertain the extent and 
 nature of the cold injury the grove was carefully examined dur- 
 ing the first week of March. It was particularly desired to find 
 out what effect, if any, the various fertilizer treatment had in 
 making the trees more or less resistant to cold injury. The
 
 Bulletin 154, Citrus Fertilizer Experiments 
 
 47 
 
 criteria used in this study were the amount of defoliation, the 
 number of twigs killed back and the distance to which they were 
 killed, and the amount and character of the new growth produced 
 after the freeze. 
 
 The individual plots showed considerable variation in the 
 amount of injury caused by the cold, plots 28, 5, 7, 27, 21, 43 and 
 39 being the most seriously injured. At the time of the freeze 
 the trees in these plots were in a weakened and unthrifty condi- 
 tion, owing to various causes, such as over-fertilization and the 
 effect of alkaline materials, discussed in detail elsewhere. The 
 fact that they were unthrifty was undoubtedly the cause of their 
 more serious injury from cold. It is difficult to express the 
 degree of injury in definite figures, but these trees showed ap- 
 proximately 85 percent defoliation, with 70 percent of the twigs 
 killed back on the average about 9 inches. The new growth 
 which was coming out was rather scanty and was weak in 
 character. 
 
 
 
 Fitf. 11- Reproduction of air and soil temperature records for the i;rove 
 during the freeze of February, 11M7 
 
 These figures may be compared with similar ones for plots 
 showing the least amount of injury. Plots 2, 1, 47, 48, 12, 13 
 and 1G were selected for this comparison. These trees averaged 
 approximately 65 percent defoliation with 30 percent of the 
 twigs killed back a distance of about 5 inches. The new growth 
 coming out was considerably more abundant and more thrifty
 
 48 
 
 Florida Agricultural Experiment Station 
 
 than on the other plots. These figures show that trees in good 
 healthy condition are more able to withstand a freeze than are 
 those in an unthrifty condition, and that the former make a 
 quicker recovery. This statement was borne out by the general 
 appearance of the trees and their subsequent behavior. No con- j 
 elusive evidence could be obtained indicating that any special 
 fertilizer treatment among those used on the better plots was 
 more effective than another in making the trees resistant to| 
 frost. 
 
 CONCLUSIONS 
 
 1. In this experiment sulphate of ammonia, acid phosphate,! 
 and high-grade sulphate of potash gave somewhat better! 
 results as measured by increase in growth, than any other| 
 mixture. 
 
 2. Good results were obtained from the use of nitrate of sodal 
 as a source of ammonia, from steamed bone and floats 
 sources of phosphoric acid, and from the low-grade sulphate, 
 hardwood ashes and the muriate, as sources of potash. 
 
 3. The use of ground limestone and Thomas slag have causec 
 injury, indicated by frenching. 
 
 4. Clean cultivation thruout the year was of considerable benefit 
 to young trees, but after a few years leads to a loss of soil 
 organic matter. It is not a desirable practice with trees ovei 
 five or six years old. 
 
 5. A large proportion of the phosphoric acid applied in the 
 fertilizer is retained in the upper nine inches of soil. Prac-l 
 tically none is leached out. 
 
 6. Much of the potash applied in the water-soluble form is re 
 tained by the soil. 
 
 7. Nitrogen, both in the organic and the in-organic form, i 
 lost in large quantity by leaching as shown by the lysemetei 
 experiments and by the analyses of the grove soils. There 
 was a slight increase of nitrogen in all plots excepting tht 
 clean culture and the unfertilized ones. 
 
 l!N'TVEl?F;!TY r.f CALiFOKNIA 
 
 iS ANGELJ3S 
 LI BRAKY