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Fluid Journal : Fluid Journal 1999-2001
3 Fluid Journal Summer 2001 fruit set (results not shown), and in- creased final yield (Figure 2). Soil B sta- tus did not influence the response of plants to foliar B (results not shown). Tobacco response Following removal of B from the growth medium, significant flower abor- tion and subsequently reduced seed production occurred in both wild-type and antisense tobacco plants where a gene is put in backwards as an experi- mental control (in which B is immobile), demonstrating that a brief deficiency of B can have a profound effect on flower- ing (Figure 3). The application of foliar B had no beneficial effect on these plants. Tobacco plants with the capacity to transport B in the phloem to flowers (transgenic) did not exhibit rapid flower abortion and in all cases produced sig- nificantly more seed than plants with limited phloem B mobility (Figure 3). With the application of foliar B, the transgenic tobacco equaled the perfor- mance of the control plants, showing that effective use of foliar fertilizers can entirely replace the need for soil B sup- ply. Reduced seed set in the transgenic tobacco grown for an extended period in 0 ppm B is a consequence of the deple- tion of all remobilizable B and the ulti- mate occurrence of B deficiency throughout the plant. Conclusions Each of these experiments demon- strates the potentially significant effect of short-term nutrient deficiencies and the role fluid fertilizers can play in main- taining a balanced nutrient supply. The results of experimentation in both pistachio and in olive, as well as many other experiments, demonstrates that foliar B application can result in correc- tion of an apparent deficiency that is not responsive to soil B application. This is most apparent in pistachio where foliar B fertilization applied pre-anthesis in- creases pollen germination, reduces blanking and non-splits (results not shown), and consequently increases yield. This stimulation occurs even in trees with summer B concentrations in excess of 150 ppm, indicating that there is a specific requirement for B in the de- veloping flower. The most effective method to ensure adequate B for flowers is through foliar application. Soil appli- cations of B are effective at raising leaf B levels but are not as effective as foliar sprays at increasing yield. Adequate leaf B levels are not a guarantee of opti- mal yield. The apparent superiority of foliar B can best be explained as a consequence of a transient inadequacy in B supply to the reproductive tissues from the soil. This may occur as a consequence of low root activity in cool soils, high B re- quirement in developing flowers, or low transport of B to the reproductive tis- sues. All of these explanations suggest that transient deficiencies of B can oc- cur and they may not be efficiently cor- rected through soil fertilization. To our knowledge, this is the clearest example of a transient nutrient deficiency and a justification for application of foliar fer- tilizers. The results here clearly demonstrate that transient nutrient deficiencies occur and can be important determinants of yield. The evidence also suggests that foliar fertilizers can, on occasions, be uniquely effective at correcting these deficiencies. Based upon these results, we conclude that transient deficiencies of nutrients may occur as a conse- quence of a combination of spatial and temporal variations in plant nutrient de- mand and supply, and will be influenced by the relative mobility of the nutrient in the plant. From our extrapolations, we further conclude it is likely that fluid fertilizers represent a powerful technique to de- liver nutrients in a balanced, effective, and efficient manner that minimizes peri- ods of transient deficiencies. Further research must be conducted to determine if transient deficiencies of other nutrients occur and if fluid fertiliz- ers play a unique role in their correction. Dr. Brown is professor in the Department of Pomology at the University of California. Figure 3. Seed yield of tobacco lines grown for 28 days with adequate B then transferred to growing medium that supplied either 0 ppm B, 0.05 ppm B to roots, or 100 ppm B spray applied to three mature leaves, Brown, U of Cal. Boron Treatment 0 ppm 0 1 2 3 Seed Yield (grams per plant) 4 Transgenic Wild-Type Antisense control 5 100 ppm foliar 0.05 ppm
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