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Fluid Journal : Fluid Journal 1999-2001
2 Fluid Journal Summer 2001 rapid re-greening of tissues is needed for aesthetic purposes. A significant commercial justification for the use of foliars is based upon the premise they offer specific advantages over soil fertilizers under certain condi- tions of high nutrient demand. Examples of conditions that prompt commercial use of foliars include 1) periods of peak nutrient demand such as during rapid fruit growth when nutrient demand can exceed nutrient supply even in a well- fertilized soil or 2) occasions when local- ized within-plant demand exceeds the capacity for within-plant nutrient redis- tribution. Although the use of foliars to over- come soil physical and chemical proper- ties is well defined and many examples of its implementation are available, use of foliars to prevent or overcome tran- sient deficiencies has received scant attention. In spite of this lack of sound experimentation it is the purported effec- tiveness of foliars at preventing and correcting transient deficiencies that is the basis for the sales of many commer- cial foliar fertilizers. What follows is experimental evidence supporting the occurrence of transient nutrient deficiencies and how they can be efficiently corrected by foliar fertiliza- tion. Also discussed are the broader implications of these results as a ratio- nale for the use of foliars. Pistachio response Table 1 compares the effectiveness of soil B applications with respect to foliar B applications. It can be seen that soil- applied B was most effective at raising tissue B levels. Plants supplied 6 or 10 oz Solubor in 1990 had tissue B concen- trations (in 1992) higher than trees that received foliar applications alone. Nev- ertheless, trees that received foliar B showed a positive yield response while those receiving soil B did not. This indicates that adequate leaf B sta- tus does not ensure optimal tree produc- tivity. Apparently foliar applications of B serve a unique role in enhancing pis- tachio fruit set. Figure 1 demonstrates that the most effective time for application of foliar B was the late dormant spray (Feb 28--- immediately pre-anthesis) in which a yield increase of as much as 20 percent over control trees was recorded. Later sprays effectively increased tissue B levels but did not increase fruit yield, even though all B sprayed trees yielded more than trees not receiving supple- mentation. The effectiveness of early but not late B sprays is evidence that B is critical for pollination or fertilization of pistachio flowers. Olive response Foliar B application immediately pre- anthesis significantly altered the ratio of perfect to imperfect flowers, increased Imperfect Flowers % Yield % of Imperfect flowers 52 36 0 246 491 737 Boron rate --ppm Figure 2. Influence of pre-anthesis foliar B on olive reproduction, Brown, U of Cal, 1999. 26 28 30 32 34 36 38 40 42 YIELD- lbs/tree 38 40 42 44 46 48 50 Table 1. Influence of B application on yield, bud and July leaf B, Brown, U of Cal. B Yield Binppm gal/tree lbs in-shell splits/tree Buds Leaves (July) Foliar 0 19 35 170 2 22 37 185 5 26 39 171 10 21 41 210 Soil 2 19 35 172 4 19 38 189 6 20 44 201 8 21 50 219
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