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Fluid Journal : Fluid Journal 1996-1998
1 Fluid Journal Fall 1996 Summary: During a four-year trial on grapefruit trees, fertigation, combined with a broadcast treatment, outproduced three conventional broadcast applica-tions in three of the four years. The four-year cumulative fresh fruit yield advantage of the combined treatmentaveraged 44 boxes/ A per year over the conventional treatment. The production increases by the combined treatment over the conventional treatment represented an 8 percent advantage. The combination treatment also provided a high-er fertilizer-use efficiency (greater production for similar application rates) than the conventional treatments. This experiment took place in the Flatwoods of Florida. Flatwoods is the term given to the level, low- lying coastal areas of the Florida peninsula that are underlain by shallow water tables. Nearly all Flatwoods citrus groves are planted on beds raised from 18 to 42 inches above the water furrow. These beds are required to allow for drainage from high-intensity summer rains and provide an improved root zone over non-bedded conditions. Even with such bedding, the rooting depth of citrus on Flatwoods Spodosols is typically lim-ited to about 18 inches. Irrigation is required on most Flatwoods soils because of low water- holding capacities of the sandy surface layers in combination with the shallow root zones. Fertigation is a common practice on young citrus trees, since they are pushed to rapidly achieve the size required to be economically productive. However, fertigation is less common on mature trees where the emphasis is more on fruit production than growth. For a variety of reasons, microsprinkler sys-tems are the predominant type of irriga-tion system. The objective of this experiment was to compare conventional broadcast fertilization with a combination of broadcast and fertigation treatments (via the microsprinkler system) on mature "Ruby Red" grapefruit trees. Responses Yield. The fertilization treatments produced significant differences in yields per tree in favor of the combination treatments during all except the first year of the study, as by Dr. Brain J. Boman Fertigation Enhances Grapefruit Yield When combined with single broadcast fertilization, fertigation of orchards pro- duces results superior to several conventional broadcast applications. shown in Figure 1. The total yield for the four years of the study was 2,071 boxes/A for the combination treatments compared to 1,897 boxes/A for the conventional treatments. The cumulative advantage for the combination treatments was 174 boxes/ A or an average annual increase of 44 boxes/A/year, as shown in Figure 2. TSS. The difference in total soluble solids (TSS) produced between the two fertilization programs was significant only in the 199 1/92 season. However, the four-year total was highly significant. Cumulative TSS produced over four years for the combination treatments averaged 9,744 lbs/A versus 9,048 lbs/A for the conventional treat-ments (Figure 2). The difference in TSS of 696 lbs/A/year resulted in an average of 174 lbs/A/year more TSS for the combination treatments compared Table 1. Fertilization dates for "Ruby Red" grapefruit trees, Boman, University of Florida, 1988-92. Treatment 1988/89 1989/90 1990/91 1991/92 Conventional Broadcast 13 Apr 21 Feb 21 Feb 27 Feb application 21 June 13 June 30 May 26 June dates 26 Oct 18 Oct 16 Oct 6 Nov Total N & K2O (lbs/A) 155 160 158 158 Combination Broadcast N & K2O (lbs/A) 52 52 52 52 No. fertigations 18 17 17 17 Fertigated N & K2O (lbs/A) 113 107 107 107 Total N & K2O (lbs/A) 165 159 159 159
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