EFFECT OF TREE SPACING ON FRUIT PRODUCTION AND NET RETURNS OF 'PINEAPPLE1 ORANGES

Proc. Fla. State Hort. Soc. 95:29-33. 1982. EFFECT OF TREE SPACING ON FRUIT PRODUCTION AND NET RETURNS OF 'PINEAPPLE1 ORANGES R. C. J. KOO AND R. P. MURARO University of Florida, IF AS, Agricultural Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850 Abstract. 'Pineapple' orange (Citrus sinensis (L) Osb.) trees on rough lemon (Citrus jambhiri Lush) rootstock were planted at spacings of, and on Astatula fine sand. fruit production over a 1 period showed that the close spaced () trees pro duced the most fruit on a per acre basis with the intermediate () and wide () spaced trees producing 95 and 75%, respectively, of the fruit produced in the close spaced trees. During last 5 yr, fruit production was highest for the intermediate spaced () trees with the wide () and close () spaced trees producing 85 and 81%, respectively, of the fruit produced in the inter mediate spaced trees. The yield of soluble solids followed the trends of fruit production. Using the yield data, past fruit price structures and grove care costs, net returns per acre were analyzed. During the first 5 yr of the experiment, the close spaced had the highest net returns per acre with the intermediate and wide spaced trees having 70% and 48%, respectively, of the close spaced trees' and net returns. The trend changed during the last 5 yr of the experiment. The intermediate spaced trees had the highest net returns per acre with the wide and the close spaced trees having 83% and 74%, respectively, of the inter mediate spaced trees' net returns. Over the entire 15 yr of the experiment, the intermediate spaced trees had the highest net return per acre with the close and the wide spaced trees having 89% and 78%, respectively, of the intermediate spaced trees' net returns. The ever increasing costs of land, production and har vesting have led Florida citrus growers to seek more efficient use of their resources. High density plantings are a common approach towards increasing this efficiency. Higher initial yields obtained by increasing the number of trees per acre could recover the high investment and development costs over a shorter period of time. The direct correlation between the number of trees per acre and fruit production at early stages of grove development have been reported (2, 8, 9, 10). The early yield advantage tends to diminish as the trees in crease in size and competition for space, light, water and nutrients becomes more intensified through time. This paper reports 15 yr of fruit production data from a tree spacing experiment initiated in 1960. Initial yield re sults have already been published (9, 10). The economic assessment of costs and returns from different tree spacings are calculated. Materials and Methods 'Pineapple' orange trees on rough lemon rootstock were planted at spacings of (6.1 x 7.6 m), (4.6 x 6.1 m) and (3.0 x 4.6 m) at the Agricultural Research and Education Center grove at Barnum City in iflorida Agricultural Experiment Stations Journal Series. 4261. 2The authors are grateful to Orange Service Company, of Clermont, Florida for providing the annual hedging and topping service in the tree spacing experimental block. Central Florida. These spacings are equivalent to, and trees per acre (215, 358, 716 per ha), respectively. Experimental design and plot layout were reported earlier (9, 10). Annual hedging was started in 1966 in the spacing and started in 1971 in the spacing. Hedg ing has not yet been necessary in the spacing. In 1975 every fifth tree in the spacing was removed to facilitate harvesting. Adjustments were made in fruit pro duction calculations to represent trees per acre. Between 1975 and 1981, fruit samples were collected an nually, juice quality measurements made and the yield of soluble solids calculated. Fruit production data were col lected at time of harvest. Results and Discussion Previously reported fruit production (9, 10) is repeated in Table 1 in order to show the trends continuing over the past 15 yr. Although the trees were planted in 1960, they were frozen to the soil bank in December 1962. All the top growth has occurred since growth resumed in 1963. Between 1967 and 1981, total fruit production per tree was highest for the wide spaced trees and least for the close spaced trees (Table 1). On a per acre basis, however, the close spaced trees () produced more fruit than the two wider spacings. The close spaced trees produced 5% more fruit than the intermediate spacing () and 37% more fruit than the wide spacing (). The relationship between tree spacing, tree density and fruit production during increments is illustrated in Fig. 1. The closely spaced trees produced twice as much fruit as the wide spaced trees and 30% more fruit than the inter mediate spaced trees between 1967 and 1971. These differ ences became less in the next 5 yr (1972-1976) when the close spaced trees produced 34% more fruit than those of the wide spaced trees and 10% more fruit than the intermediate spaced trees. The intermediate spaced trees produced the most fruit for the first time in 1977. The highest fruit pro duction ever recorded in the block was produced by the close spaced trees in 1976 which exceeded 1000 boxes per acre. In the last 5 yr () the intermediate spaced trees produced the most fruit. It was followed by wide and close spacings in that order. Should present production trends continue, the wide spaced trees may eventually equal and surpass the fruit pro duction of the two closer spaced trees. Fruit production in the close spacing may remain constant or continue to de crease unless a systematic tree removal and size management program is maintained to alleviate the crowded situation and maximize light penetration into the lower canopy. Juice quality measurements due to tree spacing were in consistent and showed little difference. Yields of soluble solids calculated for a 7-yr period between 1975 and 1981 (Table 2) reflected the trends in fruit production. Soluble solids data prior to 1975 were not available. Economic Analysis Net returns per acre were analyzed for each tree spacing using the above yield data, historical prices (3) and grove care costs (6, 7). Grove care costs were adjusted to reflect the additional equipment, labor, and materials required by the intermediate and close tree spacings (Table 3) as the grove care practices were actually performed at the grove 29

Table 1. Yield of 'Pineapple' orange as affected by tree spacing. Yearz 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1.7 by 1.5 b 3.3 b 5.2 c 3.5 c 5.5 c 4.3 b 6.0 c 8.7 c 7.5 c 6.1c 7.4 c 5.6 c 6.3 c 75.0 Boxes per tree 1.5 b 1.4 b 2.3 a 3.0 b 4.1b 3.0 b 4.9 b 4.0 b 4.5 b 6.6 b 5.9 b 4.5 b 5.3 b 2.9 b 4.7 b 58.6 1.2 a 0.9 a 2.1a 2.0 a 2.8 a 2.0 a 2.1a 3.9 a 1.8 a 1.4 a 30.7 144 a 128 a 212 a 285 a 450 a 305 a 480 a 376 a 520 a 755 a 654 b 528 a 642 b 4 b 547 a 6513 Boxes per acre 222 b 203 b 326 b 434 b 599 b 436 b 703 b 573 b 648 c 958 b 855 c 651b 772 c 417 a 682 b 8479 360 c 269 c 619 c 551c 708 c 583 c 812 c 582 b 600 b 1119c 534 a 704 c 549 a 407 a 554 a 8951 z"year" refers to production season; for example, 1967 is the 1967-68 season. ymean separation within the spacing treatments by Duncan's multiple range test, 5% level. site. Due to the small percentage acreage of the tree spacing experiment, sprayer gallonage calibration rate was the same as the remaining acreage of the 130 acre experiment station grove. Grove care costs for the intermediate and close tree spacings were usually 125% and 165%, respectively, of the cost of the wide spacing. The exceptions were cultivation where one-way discing was performed and fertilization and irrigation where the same quantity was applied to each tree spacing. Since no reset trees were planted during this 1 study, tree replacement costs were excluded from the anal ysis. Costs involving land investment and grove establishment were not included in the analysis. This cost information would be required to provide a complete investment analysis. However, such an investment analysis requires incorporating the effects of the federal income tax laws during the 1960's to derive after tax cash flows and rate of return on investment. An after tax cash flow analysis for citrus grove establishment is currently being developed for microcomputers and will be available in 1983. Table 2. Soluble solids production at different tree spacings. Year 1975 1976 1977 1978 1979 1980 1981 2680 az 3826 a 3041b 3062 a 4081b 2684 b 3050 a (lb./acre) 3370 c 4946 b 3911c 3886 b 4845 c 2301a 3682 b 3030 b 5740 c 2320 a 4238 c 3300 a 2246 a 3179 a 22424 26941 24053 zmean separation within spacing treatments of each year by Duncan's multiple range test, 5% level. The average costs and returns per acre are summarized in three periods in Table 4. Fruit prices for the period were more than double those during the and periods. This price increase was due in part to the Table 3. Schedule of grove care practices by tree spacing. Trees/ acre Cultivation disc Herbicide Pest control Post Summer Fall bloom oil miticide gal/acre Fertillb./acre Hedge General Tree Overhead grove replace- springier work, ment irrigation devine : [ 1971 only : [ I : [ Cost Adjustment Multiplication Factor Over Trees Per Acre (both ways) (one-way) Same (one-way) 1.025z 1.07z 2.15 Same Same zthe adjustment multiplication factor for fertilizer represents the additional application cost only. 30

1982 95: Hort. Fla. State Soc. Table 4. Five-year average cost and returns per acre for 'Pineapple' orange tree spacing experiment. Tree spacing Trees/ acre Delivered in price per boxz ($) Pickfc haul ($/box)y Yield per acre (boxes) Culti vation Herbi cide Pest control Fertil ization Grove care cash COStS ($)x Irri Gen. work Hedging gation & devine cost Harvest cost revenue Net income ^ 10x15 ft 243.80 356.80 501.40 4.71 5.88 4.71 10.36 12.95 17.09 35.50 44.37 58.57 28.26 38.62 40.32 0.00 1.50t 9.22 5.09 6.36 8.40 96.63 122.41 15 188.91 275.16 375.05 564.90 817.45 1,131.68 279.36 419.88 605.61 v 4.20 663.60 739.20 7.20 5.40 7.20 13.44 16.80 22.18 77.42 96.78 127.75 71.20 72.98 76.19 0.00 13.05 17.22 7.50 9.37 12.37 199.03 236.65 285.17 510.49 694.34 764.33 1,134.73 1,545.52 1,703.23 425.21 614.53 653.73 ^ 571.60 675.40 549.60 11.72 8.79 11.72 18.93 23.66 31.23 137.52 171.90 226.90 90.64 92.90 96.98 0.0. 18.71 60.01 12.35 15.44 20.38 339.73 399.97 515.80 828.75 973.83 799.16 3,015.42 3,600.60 2,969.15 1,846.95 2,226.80 1,654.19 zsource: reference (3) with 1981 preliminary price estimate. ysource: reference (4) with 1980 and 1981 preliminary cost estimates. xsource: references (5, 6) with costs indexed prior to 1972. ^Effective age 5-9 yr. veffective age 10-14 yr. ^Effective age 15-19 yr. 1 Hedging was performed only in 1971.

800, _ 600 _ g 400 200 49% 20lx25I I5'x20' rt 71% IO'xl5l S //?* 1 '<'''//. 85%?'4 'Sss. Fig. 1. Average annual fruit production in 5-year increments at 3 tree spacings. freezes incurred since January, 1977 as well as the increased demand for citrus products. Harvesting and grove care costs increased steadily throughout the three periods. During the first period, trees at the close spacing had the highest net returns per acre with the intermediate and the wide spacings having 70% and 48%, respectively, of the close tree spacing net return. In the second period net returns for trees of the intermediate and wide spacing in creased to 95% and 66% of the close tree spacing net re turns. The intermediate tree spacing net returns were high est for the last period with the wide and close tree spac ings having 83% and 74%, respectively, of the intermedi 81% ate three spacing net returns. Over the entire 15 yr of the experiment, the intermediate tree spacing had the highest net return per acre with the close and wide tree spacings having 89% and 78%, respectively, of the intermediate tree spacing net returns. Table 5 presents total and accumulative net returns per acre in actual and discounted dollars. Discounting is the method by which future dollars are equated to present dol lar values. The base year for the analysis was 1967. To develop the concept of discounting, consider its more familiar counterpart, compounding (1). Suppose an investor possesses a sum of money, say X dollars, which he can invest at an annual interest rate of r, compounded annually for n years. At the end of n years, his investment has grown to a value R where R = X(l +r)... (1 +r) n-terms R = X(l+r)n. Equivalently, a sum R received n years from today has a present value X given by x This expression is known as the present value formula. The cash flow benefit to higher early year returns is dem onstrated by the discounted values. At the 10% present value rate, the 1 accumulated net returns for the close tree spacing increased to 99% of the intermediate tree spac ing as compared to 89% of the actual dollar amount. Like wise, the wide tree spacing discounted net returns decreased to 75% of the intermediate 1 net returns as compared to 78 % of the actual dollar amount. The benefits of higher early returns is demonstrated more drmatically when a 15% present value rate is used. The intermediate tree spacing 1 net return decreased to 96% of the close tree spacing 1 net return while the wide tree spacing decreased to 66%. There are many factors to consider when selecting a tree spacing for a new citrus planting. Yield, grove care, harvest ing costs, and total future returns have been discussed and analyzed in this paper. Other factors, such as suitability of scion and rootstock combinations for high density plantings, cost of trees, planting, young tree care, fresh vs. processed fruit and after tax cash flows, should also be evaluated for high vs. low density plantings before grove establishment begins. R Table 5. Five-year total and accumulative net income per acre.... Actual dollars 1,397 2,126 9,235 3,523 12,758 2,099 3,073 11,134 5,172 16,306 2,989 3,220 8,271 6,209 14,480 Discounted dollars.. Present value rate 1,073 1,075 3,021 2,148 5,169 1,639 1,571 3,210 3,669 6,9 2,389 1,669 2,718 4,058 6,776 Present value rate 956 786 1,742 3,548 1,472 1,155 2,200 2,627 4,827 2,169 1,236 1,627 3,405 5,032

Literature Cited 1. Abbitt, Ben, R. P. Muraro, and T. H. Spreen. 1979. A method for estimating net total loss from losing a citrus tree. Inst. Food Agr. Sci. Econ. Information Rep. 105. February. 2. Boswell, S. B., E. M. Nauer and D. R. Atkin. 1982. Performance of 'Navel' oranges at different spacings. Calif. Citrog. 67:207-212. 3. Boswell, S. B., C. D. McCarty, K. W. Hench and L. N. Lewis. 1975. Effect of tree density on the first ten years of growth and produc tion of Washington navel orange trees. J. Amer. Soc. Hort. Sci. 100: 370-373. 4. Florida Citrus Processors Assoc. 1981. Statistical Summary, 1980-81 Season. Winter Haven, FL. 5. Hooks, R. C. and Richard L. Kilmer. 1981. Estimated costs of picking and hauling fresh Florida citrus, 1979180 season. Inst. Food Agr. Sci. Econ. Information Rep. 151. 6. Muraro, R. P. 1982. Budgeting costs and returns: central Florida citrus production. Inst. Food Agr. Sci. Econ. Information Rep. 160. 7. Muraro, R. P. 1972-1982. Comparative citrus budgets. Univ. Florida, Agr. Educ. Center, Lake Alfred, FL. 8. Passos, D. S., A. P. Cunha, Y. S. Coelho and E. M. Rodriques. 1977. Behavior of orange trees under three spacings in the state of Bahia, Brazil. Proc. Int. Soc. Citriculture 1:169-171. 9. Phillips, R. L. 1969. Performance of closely spaced trees. Proc. Fla. State Hort. Soc. 81:48-51. 10. Phillips, R. L. 1974. Performance of 'Pineapple* orange at three spacings. Proc. Fla. State Hort. Soc. :81-84. Proc. Fla. State Hort. Soc. 95:33-37. 1982. DEVELOPMENT OF THE ROOT SYSTEM OF YOUNG 'VALENCIA1 ORANGE TREES ON ROUGH LEMON AND CARRIZO CITRANGE ROOTSTOCKS1 Kenneth B. Bevington2 University of Florida, Institute of Food and Agricultural Sciences, Fruit Crops Department, Gainesville, FL 32611 William S. Castle University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850 Additional index words, citrus, root observation chamber, morphology, seasonal periodicity. Abstract. Root observation chambers were used to study the seasonal pattern of root growth and the morphological development of the root system of young citrus trees. The trees were 'Valencia' orange (Citrus sinensis (L.) Osb.) on rough lemon (C. jambhiri Lush.) and Carrizo citrange (Poncirus trifoliata (L) Raf. x C. sinensis) and were planted in the chambers August 1981. New root growth was evident within 2 to 3 wk of planting and after 3 months had reached a depth of 90 cm. By April 1982, root growth was evident below 150 cm. Replacement roots, which developed from the ends of the taproots and main laterals severed during transplanting from the nursery, were largely responsible for the rapid expansion of the root system. The rate of root growth declined during peak periods of shoot growth but increased markedly immediately following the cessation of each shoot flush, especially the emergence of higher order laterals. root growth was apparent during winter. Dif ferences between rootstocks were evident in the rate of root growth and in the morphology of the root system. The citrus tree root system is comprised of a relatively shallow, well-branched framework of woody laterals bearing bunches of fine fibrous roots (1, 7). The fibrous roots grow in all directions from the woody framework and are usually most densely concentrated near the soil surface. The main lateral roots radiate out from the trunk and may extend up iflorida Agricultural Experiment Stations Journal Series. 4356. Specif &&\&s to Roland L. Dilley, Florida Citrus Nursery, Avon Park, for providing the trees for this study. agraduate Research Assistant. to 2 to 3 times the spread of the canopy. The taproot is cut back during transplanting and is usually not well developed. However, several vertically oriented smaller roots may arise from the severed taproot and penetrate to considerable depth (9). Characteristic differences in root system morphol ogy exist between rootstocks; but, the development of the root system is modified by soil conditions and cultural practices (1). The growth dynamics of the root system in relation to environmental factors and the developmental relationships between the various types of roots that comprise the root system have been little studied in citrus. These aspects of root growth are important because the rate of elongation determines the rate at which the root system exends into new areas, while the relative amount of elongation of the different types of laterals determines the pattern and ef ficiency with which the soil volume is exploited (10). The lack of information reflects the technical difficulties involved in observing root growth under field conditions. At the Agricultural Research and Education Center, Lake Alfred, large root observation chambers were in stalled at a field site with the objective of studying the seasonal pattern of root growth and the rate of development of the root system. This paper describes the early morpholog ical development of the root system of young citrus trees. Materials and Methods Root observation chambers. Six root observation cham bers were constructed. Each chamber consists of 2 sheets of 6.4 mm Plexiglas attached to the front and rear of a timber frame. The Plexiglas sides are covered with removable metal shutters to exclude light. The internal dimensions of each chamber are 180 cm top to bottom, 88 cm wide, and 15 cm front to rear. The viewing surface is 3.2 m2 and the soil vol ume 0.25 m3. Drainage is provided by a single, mesh-covered outlet in the bottom of the chamber. The chambers are in stalled in underground metal retaining frames at a field site (Fig. 1). A manually operated hoist system is used to peri odically lift the chambers from beneath the soil surface for root observation. For this particular study, each chamber was filled with untreated Candler fine sand so that the original soil profile was maintained. The 6 chambers were planted in August 1981 with 16-month-old bare-root nursery trees obtained from a commercial nursery. The trees were 'Valencia' or ange budded on rough lemon and Carrizo citrange and 33