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Fluid Journal : Fluid Journal 2008-2009
Figure 4. Fiber micronaire as affected by water supply as well as P application method and rate. recommendation of private and public labs is 5:2. Again, as water supply increased, both seed and fiber yields increased with the response to method of application being consistent (Figure 2). Increasing N:P ratios increased yields only slightly, with the 5:2 consistently being the lowest producer of the three ratios being compared. Seed index Seed yield increases were due to both more harvested bolls/A and increased seed size as indicated by the seed index (Figure 3). Seed index responses to P differed from that seen for total seed yield. The anomaly seen in the 5:2 N:P ratio was due to fewer harvested bolls resulting in heavier seed weights for each fruit. Fiber Micronaire Fiber and seed maturity as measured by fiber micronaire and seed density were significantly affected by both application method and N:P ratio within the fertigation treatments (Figure 4). Fiber maturity declined with increasing yield as water supply increased for both the control and the preplant P treatments. Sidedress applications significantly increased fiber maturity due to both reduced boll numbers (resulting from root pruning) and enhanced P supply during the fruiting period as compared to the preplant treatment. Increasing the P supply during the fruiting period through fertigation resulted in increases in micronaire as water supply increased yield. Increased seed and fiber maturity means better prices for both seed and lint from the producer perspective and better finished products from the consumer perspective. Seed Density Figure 3. Seed index 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. Seed density is indicative of seed maturity and seedling vigor. Seed density less than 1.0 g/cm3 is indicative of immaturity and results in reduced viability and reduced seedling vigor. Averaged across years and varieties, seed density was found to be greater when in-season P was fertigated on the cotton crop (Figure 5). As lint and seed yields increased due to increasing water supplies, seed maturity remained fairly constant when fertigated, whereas fiber
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