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Fluid Journal : Fluid Journal 1993-1995
2 Fluid Journal Spring 1995 the role it plays in the flowering process. To accomplish this and better assess the behavior of boron in plants, experiments were designed and conducted on pistachio trees by our research team from 1990 through 1992. Site of the study was the central valley of California. The results of our work, as reported in this article, are helping us to better under-stand the role of boron in plants. Foliar feeding superior It is clear from our trials that foliar applications of boron on pistachio trees are the most effective method to ensure adequate boron for the flowers and increase yields (Figure 1). Trees that received foliar applications through the three years of trial continue to respond to supplemental sprays. Note in Figure 1 that the three-year cumulative yield per tree increased with foliar boron concentrations up to 5 lbs/I 00 gals, but decreased at the higher rate. It is significant that 5 lbs was shown to be the optimum rate in two of the three years. This was true even in trees growing in different soils with inherently different boron levels in their tissues. The three-year cumulative yield for pistachio demonstrates that treatment with 5 lbs Solubor/100 gals resulted in an approximate overall 20 percent increase in yield for this period. Soil treatments did not significantly increase yield, though July boron levels should not be reduced below 120 ppm. The 20 percent yield increase is a significant economic benefit. Notably, these results were obtained in soils that were not particularly boron deficient. Greater yield response in boron- deficient regions would be expected. Foliar sprays of boron also resulted in a decrease in the number of blanks and non-split nuts (Figure 2), which may account for part of the yield increase. Preliminary calculations suggest that the reduced number of blank nuts in the 5-lb foliar treatment may account for 65 percent of the observed yield difference. This finding clearly suggests that foliar boron increases crop yield through its effect on pollination or fertilization of the pistachio flower. It is also evident at all times and in all treatments that the yield of trees 012345678910 B Application Rat (lbs Solubor/100 gal.) PGI Atlantic Average % Blanks 30 28 26 24 22 20 18 16 14 12 10 012345678910 B Application Rat (lbs Solubor/100 gal.) PGI Atlantic Average Tree Yield (lbs) 75 70 65 60 55 50 45 40 Figure 2. Effect of boron foliar treatment on percent of blanks in pistachio, Brown, et al., University of California. Figure 3. Effect of boron foliar treatment on yield of pistachio, comparing Atlantica and PGI rootstocks, Brown, et al., University of California. using the Atlantica root stock was from 10 to 25 percent less than PGI (Figure 3). Carryover Soil. Two years after soil boron appli-cation, July leaf analysis showed a small residual effect of the earlier application. In sites with heavier soils, this carryover was even more evident. Soil applications of boron did not increase bud boron levels until one year or (in the case of heavier soils) two years after application. This indicates that soil applications of boron may not be effective in increasing bud boron concentrations in the following season.
Fluid Journal 1996-1998