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• W1963535877 abstract "The citrus industry recently added over 160 000 acres of new groves in south Florida. Young, densely-planted groves are typically fertilized in excess of current guidelines in an effort to accelerate fruit production. The objectives of this study were to develop an efficient N fertilization program for maximum initial orange (Citrus sinensis L. Osb.) production, to assess the use of controlled-release N, and to ascertain the effect of soil pH on tree growth and yield. ‘Hamlin’ orange trees on Carrizo citrange rootstock were planted at 194 trees/acre in 1989 on a sandy Alfisol, and were grown for 4 yr under four fertility levels. In the first 3 yr, four relative rates (12.5, 25, 50, and 100%) of a complete (N-P-K) fertilizer were applied using three N sources (ammonium nitrate [AN], a 50/50 mixture of AN and isobutylidene diurea [AN-IBDU] and a 60/40 mixture of AN and methylene urea [AN-MU]. The 100% rate consisted of 6, 12, and 18 lb/tree of 8-4-8 fertilizer applied in Years 1, 2, and 3, respectively. In the fourth year, N was applied at 41, 81,163, and 325 lb/acre to trees that received the same relative rates the previous 3 yr. Tree canopy volume and orange yield increased as N rate increased. In the fourth year, canopy volume at the lowest fertility level was 90% of that at the highest level (534 vs. 603 cu ft), but orange yield was only 63% as great (328 vs. 518 boxes/acre, where 1 box = 90 lb of oranges). A quadratic-plateau model suggested that maximum yield could be obtained with about 250 lb N/acre in the fourth year. However, 91% of maximum yield was obtained with 163 lb N/acre. A leaf N concentration of 2.35% or greater was associated with maximum yield. As N increased, orange peel color was greener, juice acid concentration increased, total soluble solids (TSS):acid ratio decreased, and TSS yield per acre increased. The major advantage of controlled-release N was lower application frequency compared with water-soluble N. No relationship between soil pH and tree canopy volume or orange yield was observed in the pH range of 4.6 to 8.0. Below pH 4.6, tree size and yield were depressed. Current guidelines for fertilization appear to be sufficient for maximum early orange yield in high-density new plantings on south Florida flatwoods soils. Research Question Planting of citrus trees occurs continuously, either as solid set new groves or replants in established groves. Since 1980, over 160 000 acres of new citrus groves have been planted in south Florida, where mild winter temperatures allow for uninterrupted growth. Young trees, which are planted at two to three times the traditional population per acre, have been fertilized in excess of current guidelines in an effort to accelerate fruit production. This study was designed to develop an efficient N fertilization program for maximum initial orange production in these groves, to assess the use of controlled-release N, and to examine the effect of soil pH on tree growth and yield. Literature Summary In Florida, replant volume alone can total up to 16 000 acres of new citrus trees each year. Fertilizer rate studies with young orange trees in the 1950s and ′60s led to the current recommendations for trees from 1 to 4 yr of age. Experiments carried out in a variety of locations in the 1980s suggested that the first-year N recommendation exceeded that required for maximum growth, especially where controlled-release N was used. These studies were terminated after the first or second year, however, and were not long enough to evaluate fertilizer treatments with respect to fruit yield. Soil pH, which is highly variable in south Florida, can affect tree performance. Research on Entisols of central Florida showed an increase in tree growth as the soil pH increased from 5.0 to 7.0. However, no studies of pH effects on citrus tree growth have been done on south Florida Spodosols or Alfisols, where soil chemical characteristics can differ. Worldwide, high performing citrus groves can be found on soils with pH ranging from 4.8 to 7.5. Study Description A subirrigated, high-density (194 trees/acre) new planting of ‘Hamlin’ orange trees on Carrizo citrange rootstock were grown on an Alfisol under four fertilization regimes beginning in March 1989. In the first 3 yr, fertilizer treatments included all combinations of four complete (N-P-K) fertilizer rates (relative rates of 12.5, 25, 50, and 100% of the recommended rate in each year) and three N sources (ammonium nitrate, a 50/50 mixture of ammonium nitrate and IBDU, and a 60/40 mixture of ammonium nitrate and methylene urea). The 100% rate was 6, 12, and 18 lb/tree of 8-4-8 fertilizer in Years 1 through 3. In the fourth year, N was applied at 41, 81, 163, and 325 lb/acre to trees which received the same relative rates the previous 3 yr. Potassium was applied at 230 lb/acre, and no P was applied. Fertilization regime effects were measured in terms of tree size, fruit yield, and fruit/juice quality. Applied Questions How did tree size and orange yield relate to N fertilizer regime, and how can the relationship be used to determine fertilizer rates for young orange trees? Tree canopy volume and orange yield increased as N rate increased, but the magnitude of their responses differed greatly (Fig. 1 and 2). while tree canopy volume differed by only 10% between the lowest and highest fertilizer rates at the end of 3 yr, corresponding orange yields measured 9 mo later differed by 37%. It is important to carry young-tree fertilization studies through to the bearing years, because the importance of fertilizer rate to tree performance was not adequately described by volume measurement alone. Current fertilization guidelines appear sufficient for maximum early orange yield in high-density new plantings; however, profitability might be increased by decreasing the N rate (especially in years of low fruit prices), since doubling the fertilization regime from 50 to 100% of maximum increased orange yield by only 9%. Fertilization decisions should be made on a year-to-year basis, because in years of high fruit prices, fertilizing for maximum yield may be the most profitable circumstance. Figure 1Open in figure viewerPowerPoint Response of spring 1992 orange tree canopy volume to application of varying percentages of the recommended fertilizer rate from 1 through 3 yr after planting. What was the effect of including controlled-release N in the fertilization programs? Controlled-release N was used successfully as a component of the fertilizer programs, but it offered no advantage in terms of higher yields at lower rates than all water-soluble N (Fig. 2). Its main benefit lies with decreased application frequency. The economics of controlled-release N are governed by its price relative to conventional N sources, and the fertilizer application method (e.g., mechanical vs. hand application). How did soil pH affect tree growth and yield? Figure 2Open in figure viewerPowerPoint Response of orange yield to application of N fertilizer in the fourth year after planting. Orange trees were planted in soil with pH between 4 and 8, but growth and yield were not detrimentally affected unless the pH was below 4.6. Excess soil Cu from fungicide applications apparently was not a factor, thus decreased growth possibly was due to Al toxicity. In new groves on previously uncultivated land, liming of soils which are below pH 4.6 is necessary for optimum growth and yield, but raising the pH up to the recommended level of 6.5 is probably not necessary until soil analysis detects an accumulation of Cu." @default.
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• W1963535877 date "1993-10-01" @default.
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• W1963535877 title "Program Fertilization for Establishment of Orange Trees" @default.
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• W1963535877 doi "https://doi.org/10.2134/jpa1993.0546" @default.
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