328 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 SOME EFFECTS OF NITROGEN, PHOSPHORUS AND POTASSIUM FERTILIZATION ON THE GROWTH, YIELD AND FRUIT QUALITY OF PERSIAN LIMES Seymour Goldweber, Manley Boss, and S. John Lynch University of Miami Coral Gables A paper published before this society in 1953 reported some effects of nitrogen, phos phorus and potassium fertilization on the con stituents of Persian lime fruits (3). At that time, the first full crop year, the harvest had not been completed for the year, therefore no yield data were available. At this reporting, complete yield records for the crop years of 1953, 1954, and 1955 are available and are used in this paper. In addition to yield data, yearly growth records from 1951 to 1956 have been compiled and are herein reported. - Citrus responds to fertilization on the oolitic limestone soils of South Florida. Nitrogen has been found to have a strong effect on tree growth, yield, and quality of citrus fruit (6, 8 & 9). Heavy nitrogen fertilization increased tree growth and yield; however, it decreased citrus fruit size, anbl also tended to depress slightly the soluble solids of the juice in some years (5). The effect of phosphorus on.citrus trees has been difficult to measure in field trials, except where deficiencies occurred. In California, the responses of citrus trees to phosphate fertiliza tion were conspicuous. Phosphate applications increased yields and reduced fruit sizes (1 & 2). Malcolm (4) reported that in groves where a relatively low and uniform supply of water soluble phosphorus was maintained, trees were in excellent condition. In areas where a high water soluble phosphorus level was maintained, the trees showed no evidence of injury, but showed no benefit. The exact roll of potassium is not known in plant nutrition. Citrus trees exhibit a marked response to varying levels of this nutrient. Sites (7) reports that under field conditions a potassium deficiency in the Duncan grape fruit depressed growth, produced small fruit, and decreased soluble solids, citric acid and Vitamin C. The acid content of the juice in creased, and the solids/acid ratio decreased in fruit produced by trees supplied with pot ash applications ranging up to 10 per cent in the fertilizer mixture. A low rate of potas sium fertilization produced a high proportion of early maturing, well colored, small citrus fruit having a relatively high total soluble solids content of the juice and a low total acid (6). Experimental Methods The data contained in this report are a continuation of the investigations initiated in 1950. The report presented before this Society in 1953 covered experimental design, analyti cal methods, and preliminary findings (3). The fertilizer tests on the Idemore variety have been discontinued, and this paper deals with data on Persian limes. Nitrogen, phosphorus, potassium and cal cium analyses of lime juice have been discon tinued, but the levels of these elements in the tree as represented by foliar analysis will be investigated and reported upon at a later date. Increases in trunk growth between the years 1951 and 1956 were obtained by measuring the trunk circumferences in inches, using a flexible steel tape, at a permanently marked level on the trunk. These measurements were then converted to transverse area. Tree con dition was estimated by giving a relative value from 1 to 10, for each treatment, with respect to the tree size. Another similar value was given with respect to depth of green color in the leaves and foliage density. The rate of application of fertilizer has in creased with tree size. Interval of application is continuing at 60 days, at the present time. Magnesium calculated as MgO, has been in creased to 4 per cent in all fertilizer mixes.
GOLDWEBER, ET AL: LIME FERTILIZATION 329 Experimental Results Per Cent of Juice in Fruits, 1956 Crop: In crease in fertilizer nitrogen levels resulted in an increase in the percentage of juice in the fruit (Table 1). A greater difference in per cent juice occurred between the 2 to 4 per cent nitrogen levels than between the 4 to 6 per cent levels. High nitrogen levels seemed to be most effective when coupled with high potassium levels. Heavier applications of potassium also favored increases in per cent juice content, but to a much lesser degree than nitrogen. At present no effect of\phosphorus can be ob served. Soluble Solids, 1956 Crop: Higher m'trogen levels seemed to cause an increase in per cent soluble solids (Table 1). Potassium had the opposite effect in that the higher the potassium level, the lower the percentage of soluble solids. Again, phosphorus seemed to have no effect on this juice constituent. Titratable Acid, Solids/Add Ratio, 1956 Crop: Titratable acid was apparently in creased with increasing nitrogen levels and especially so when coupled with high potas sium (Table 1). Increasing levels of potassium also yielded a positive increase in titratable acid. Phosphorus seemed to be ineffective on the percentage of titratable acid in lime juice. Variation of nitrogen, phosphorus, and potas sium levels in fertilizer application did not show any observable changes in the solids/ acid ratio of lime juice. Number of Fruit Per Tree (1953-54-55 Crops): An increase of nitrogen in the fertili zer generally results in a marked increase in table i. effects of fertilize}* treatments on some CONSTITUENTS OF PERSIAN LIME FRUIT. (1956 Crop) TREATMENTS JUICE BY WT. SOLUBLE SOLIDS TITRATABLE ACID SOLIDS ACID N P K Ratio 2-6-0 2-9-3 2-0-6 2-6-6 2-3-9 2-9-9 4 47.7 50.0 47.2 46.2 51.4 9.4 9.6 9.4 9.6 5.6 5.7 1.* 4-9-0 4-9-3 4-6-6 4-0-9 4-3-9 4-9-9 5 51.9 53.8 54.3 51.2 49.6 5.4 6.3 6-3-0 6-6-0 6-9-3 6-0-6 6-6-6 6-3-9 51.4 53.2 53.6 53.2 55.5 55.6 10.5 9.8 5.4 6.3 6.2 6.1 1.9
330 FLORIDA STATE HORTICULTURAL SOCIETY, 4956 the number of fruit per tree (Table II). Ap proximately 100 per cent increase in fruit number occurred between the 2 to 4 and 4 to 6 per cent nitrogen levels when the phos phorus and potassium levels were held at 9 and 3 per cent respectively. Increased levels of potassium also yielded a greater number of fruit per tree. The most positive results of fruit number from potassium effect were ob tained when comparatively high nitrogen levels were present. Variations of phosphorus levels in the fertilizers produced no conclusive results on fruit number. Fruit Yield Per Tree (1953-54-55 Crops): Total yield was greatest with high nitrogen levels (Table II). Generally, the yield in creased horn approximately 75 to 300 per cent with each 2 per cent increment increase in nitrogen fertilizer level. Increasing levels of potassium also resulted in higher yields. The 6 and 9 per cent potassium fertilizers generally increased production 50 to 125 per cent over 0 per cent levels. Phosphorus fertili zation seemed to show no consistent yield in crease. Individual Fruit Weight (1953-54 - 55 Crops): Variations in the levels of nitrogen fertilizers evidenced no conclusive results as to effects upon individual fruit weight (Table II). Heavier fruit were obtained, however, with increased potassium fertilization. High levels of potassium produced the greatest re sults when coupled with high levels of nitrogen and phosphorus. Phosphorus fertilization in creased the individual fruit weight slightly. Growth and Tree Condition: The rate of growth as represented by per cent increase in transverse area of tree trunks between the TABLE II. EFFECTS OF FEhTILIZER TREATl^NTE» ON YIELD, GROWTH, AND TREE CONDITION OF PERSIAN LIfciES. 1953-54 - 55 TRUNK TREE COND., 1-10, 1956 TREAT MENTS avg./tree/yr. NO. OF YIELD FRUITS IN LBS. AVG. 1ST. PER FRUIT IN LBS. AREA INCREASE 1951-56 RELATIVE SIZE RELATIVE LEAF COLOR NPK 2-6-0 2-9-3 2-0-6 2-6-6 2-3-9 2-9-9 58 107 134 100 51 372 11.14 22.56 31.56 21.29 10.39 26.42 0.24 0.20 723 663 509 661 575 691 3.8 4.8 5.0 4.3 4.7 4.8 4.7 5.0 4.5 6.7 4-9-0 4-9-3 4-6-6 4-0-9 4-3-9 4-9-9 381 624 1200 456 699 636 27.81 39.87 77.14 35 48.88 45.46 0.22 780 682 835 401 1055 748 7.0 5.3 7.5 3.5 3.8 * 7.2 5.5 8.0, 3.5 7.2 6-3-0 6-6-0 6-9-3 6-0-6 6-6-6 6-3-9 729 492 1239 744 966 975 43.55 30.97 78.42 50.18 69.71 67.09 0.18 0.20 0.22 869 912 1600 821 999 670 8.2 8.8 8.0 2.3 7.8 6.8 4.2 8.3
GOLDW.EBER, ET AL: LIME FERTILIZATION 331 years 1951 and 1956 was greater with the higher levels of nitrogen in the fertilizer (Table II). Generally the rate of trunk growth increased approximately 15 per cent with each 2 per cent nitrogen increment in crease depending upon phosphorus and potas sium levels. A greener leaf and a relatively greater tree size were also the results of higher nitrogen fertilization. Higher levels of potas sium seem to have a depressant effect on trunk growth, relative tree size, and leaf color. However; field observations have shown marked die-backs all the way to major branches in 0 per cent potassium levels. This was es pecially noted in the concomitant high nitro gen levels. Increases in phosphorus levels seemed to increase trunk growth and relative tree size as much as nitrogen, but did not seem to affect leaf color. Discussion The general trends of fruit composition and fruit weight resulting from fertilizer variations were observed with the first crop year in 1953. Subsequent observations during the succeed ing years have confirmed many of the initial findings. Fruit harvested from the 1956 crop year have shown the importance of moderate to high nitrogen fertilization. Per cent juice, soluble solids, titratable acid, number of fruit, and total yield were increased with higher levels of nitrogen. However, the greatest dif ferences between any two levels of nitrogen generally occurred between the 2 to 4 per cent applications. It was quite evident from tree condition, tree size, and fruit yield that fertilizing at the 2 per cent nitrogen level was decidedly uneconomic. Not only is the fruit yield too low to be considered practical, but tree loss, heavy incident of dead wood, and general poor appearance of the fruit were further evidence that this low nitrogen range is only of academic interest on the oolitic soils of Dade County. General fruit composition and production were also favorably affected by increased levels of potassium fertilization. Observations indicated that high levels of this nutrient, coupled with high nitrogen, are necessary for maximum production. The present fruit composition and yield data have shown no conclusive effects from phosphate fertilization above the 3 level. This finding is of both practical and academic in terest when it is considered that the test trees are now six years old. An interesting observation on the aspect of limiting factors may be noted in Table II. The absence of phosphorus or potassium usual ly results in comparatively low yields. Tree growth and tree condition were di rectly affected by variations in nitrogen, which, of course, shows the importance of this nutrient in the South Florida grove soils. The great increase in growth and better tree con dition which resulted from each additional increment of nitrogen seems to indicate, at present, that optimum nitrogen levels have not been approached. The present positive effect of phosphorus on tree growth and its ineffectiveness on fruit composition and yield seems an apparent anomoly. Continuing field observations and data will be necessary to resolve this ques tion. Also, the present depressant effect oi increased potassium on tree growth and con dition will be assured only with time. The possibility of a detrimental chloride effect from muriate of potash should not be over looked. Summary Nitrogen level increases (2-4-6) in the fertilizer treatments of Persian limes on oolitic limestone soils resulted in increases in per cent juice, soluble solids, and titratable acid in fruit, but had little effect on the solids/acid ratio of the juice. The same nitrogen varia tions resulted in increased number of fruit per tree and total yield, but did not affect individual fruit weight. Also, the rate of growth, relative tree size, and general leaf color were increased by increasing nitrogen. Phosphorus level increases (0-3-6-9) in the fertilizer treatments on Persian limes on oolitic limestone soils had no observable ef fect on per cent juice, soluble solids, titratable acid, or solids/acid ratio in the fruit. How ever, phosphorus level did affect positively trunk growth and relative tree size of the Persian lime trees under treatment. Increas ing phosphorus levels did not increase the number of fruit per tree or total yield of fruit. Potash level increases (0-3-6-9) in the fertilizer treatments of Persian limes on oolitic limestone soils increased per cent juice and titratable acid, but decreased soluble solids of the fruit. Increasing levels of potassium in-
332 FLORIDA STATE HORTICULTURAL SOCIETY, 1956 creased the number of fruit per tree, total yield, and individual fruit weight of Persian limes. Potassium seemed to have a depressant effect on trunk growth, relative tree size and leaf color. LITERATURE CITED 1. Embleton, T. W., J. D. Kirkpatrick, Winston W. Jones, and Clarence B. Cree. Influence of applica tions of dolomite, potash, and phosphate on yield and size of fruit and on composition of leaves of Valencia orange trees. Proc. A. S. H. S., 67:188-190. 1956. 2 W. W. Jones, and J. D. Kirk patrick. Influence of applications of dolomite, potash, and phosphate on quality, grade, and composition of Valencia orange fruit. Proc. A. S. H. S., 67: 191-201. 1956. 3. Lynch, S. John, Seymour Goldweber, and Clar ence E. Rich. Some effects of nitrogen, phosphorus and potassium fertilization on v the constituents of Persian lime fruits. Proc. Fla. State Hort. Soc, ft?: 224-227. 1954. 4. Malcolm, J. L. Water soluble phosphorus and potassium in the soil of lime and avocado groves in Dade County. Proc. Fla. State Hort. Soc, 64:285-292. 1951. 5. Reuther, Walter and Paul F. Smith. Relation of fertilizer treatment to fruit quality of Valencia oranges. Proc. Fla. State Hort. Soc, 64:29-35. 1951. 6. Sites, John W. The effect of variable potash fertilization on the quality and production of Duncan grapefruit. Proc. Fla. State Hort. Soc, 63:60-61. 1950. 7 and Edward J. Deszyck. Effect of varying amounts of potash on yield and quality of Valencia and Hamlin oranges. Proc. Fla. State Hort. Soc, 65:92-98. 1952. 8. Smith, Paul F. and Walter Reuther. Mineral nutrition of fruit crops. Norman F. Childers (Editor). Somerset Press, Somerville, N. J. Chapter 6, pp. 223-256. 1954. 9. van der Merwe, A. J. Nitrogen nutrition of citrus in the nitrate and ammonium form. Sci. Bull. No. 299, Hort. Series No. 14. Union of South Africa Dept. of Agr. Govt. Printer, Pretoria. 1952-1953.