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Fluid Journal : Fluid Journal 2008-2009
by prevailing temperatures. Phosphorus plays an important role in plant metabolism. The most essential function of P in plants is in energy storage and transfer. Almost every metabolic reaction of any significance proceeds via P derivatives. Figure 1. Lint and seed yield as a function of P application method averaged across years, varieties, and water supplies. Figure 2. Lint yield as a function of P application method and N:P ratios using fertigation across irrigation water supply. Data are averaged across 3 years and 4 varieties. Fertigation is an ideal conduit for supplying nutrients to developing cotton plants throughout the growing season, thereby increasing seed production and quality, as well as maximizing water use efficiency. Water supply, which directly impacts the supply of reduced C and N for growth and development, determines the number of bolls retained on the plant. Nutrient uptake parallels dry matter accumulation rate. Nitrogen and P accumulation increase very rapidly beginning at first flower and reaching a peak about three weeks later. As a result of the uptake curve, it is highly probable that the P supply in the top third of the fruit of the plant limits seed growth rate more than temperature limitations. An adequate amount of P has been shown to be crucial to the development of reproductive parts and seed formation. Currently, the primary method of applying P is either by all preplant or a sidedress application (10-34- 0) after the crop has begun growing. Nutrient management in conjunction with water supply should increase retention of fruit from the first three to four weeks of flowering, which will allow seed and fiber development to occur under more optimal temperature conditions. Also, by providing a readily available, soluble supply of P throughout boll development, seed development of the late-set bolls may occur in a more normal manner.Fertigation Excels The three years of trials offered considerable difference in both rain and temperature, which affected seed and fiber yield and quality. Averaged across years and water supplies, fertigation produced the highest seed and fiber yields as compared to other methods of P applications (Figure 1). Preplant P out-yielded sidedress applications largely due to root pruning by sidedressing at the flowering stage. Within the fertigation treatments, 5:2 N:P ratio was always lower yielding than the 5:1 or 5:3 ratios. Interestingly, the most common
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