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Fluid Journal : Fluid Journal 2008-2009
Dr. Derrick Oosterhuis !"#$%&' !"#$%&'()*+,-&'(*"(./0(1'+%2(10,.%'%30,(1*+-2&.%*- !"#$%! !"#$%&'()*+%,--. /012%345%602%75%899:$%;<= !"#$%&'()%"*+',--%".*/")01'2$./"3&' !"#$%&'#()&*+%&'+%&, !""#$%&'$()*+*,(-#.+/0+1&.0+0$',02+0&2#3+1(2)$)4+(2+#&'0+&5'02)(()+5(2+1&6$1-1+057%$0)%38 Summary: Nutrient deficiencies often occur for a variety of reasons, but can be rectified by timely applications of the deficient nutrient. This usually entails some sort of soil application but, after canopy closure during flowering and fruit development, foliar applications may be more appropriate. Foliar fertilization is a viable means of applying certain fertilizers that can supplement traditional soil methods. It can be used to improve the efficiency of a nutrient urgently required by the plant to produce maximum growth, yield, and fiber quality. In this way, foliar fertilization supplements soil applications for a more efficient supply of nutrients to the developing cotton plant for optimum yields and fiber quality. In general, foliar applications should be made early morning or late evening for maximum efficiency, and no foliar applications should be made to water-stressed plants. As with any practice, certain precautions should be observed. Optimal productivity in cotton requires that nutrient deficiencies, which occur for a variety of reasons, be avoided. Most of these can be rectified by timely applications of the deficient nutrient. In crop production, this usually entails a soil application or foliar applications that may be appropriate after canopy closure during reproductive development or when a specific nutrient is urgently required. There is a wealth of literature about foliar fertilization that was first used as long ago as 1844 to correct plant chlorosis with foliar sprays of iron. Foliar fertilization has only caught on in row-crop production in the last two decades, although there is still some speculation about the benefits and correct implementation of this practice. Foliar application of specific nutrients is a method used to improve the efficiency of fertilizer use and increase yields. The increased use of foliar fertilizers in crop production in the last decade is due in part to changes in production philosophy. In cotton, for example, the change to cultivars that fruit in a shorter time and mature earlier has placed greater emphasis on understanding plant uptake and use of nutrients. Current crop monitoring techniques also focus attention on plant development and make it easier to combine concomitant nutrient monitoring, allowing remedial action on a timelier basis. Cotton also lends itself to foliar fertilization because of the large number of aerial applications that are already made for pest control. While there are many reports on research involving soil-applied fertilizer, there are relatively few definitive studies on the usefulness of foliar fertilization in cotton. Variable yield responses to foliar fertilization have been reported. These are probably associated with incorrect timing of applications, the use of inappropriate fertilizer materials, insufficient attention to soil- available nutrients, the size of the boll load, and environmental conditions. A reliable soil analysis constitutes the basis of a successful fertilizer program and tissue analysis plays an integral part of this program for fine-tuning midseason tissue nutrient concentrations and remedying any possible deficiencies. The efficiency of foliar fertilization can be influenced by type of fertilizer, concentration and pH of the solution, use of adjuvants, and compatibility with other agrochemicals. Attention also needs to be given to rate and timing and incorporation of foliar feeding into existing production practices. Beware water stress The basis for foliar fertilization is that certain fertilizer nutrients are soluble in water and may be applied directly to the aerial portions of plants. The nutrient enters the leaf mainly by penetrating the cuticle or possibly through the stomata before entering the plant cell where it will be metabolized. For foliar fertilization to work, nutrients must be applied to the leaf, penetrate the cuticle or stomata to enter cells and metabolic pathways. The cuticle is a waxy layer that protects all plant surfaces thereby presenting a barrier to the absorption of foliar-applied fertilizers. For example, in cotton, water deficit has been shown to increase cuticle thickness 33 percent. More importantly, water stress also changes the composition of lipid
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