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Fluid Journal : Fluid Journal 1999-2001
3 Fluid Journal Spring 2000 At 3 and 5 GPM/A, lint yield responded to added P but increasing P rates did not significantly increase lint yields (Figure 1). The 5:1 ratio provided the largest yield increases and used less P fertilizer. Lack of a yield response at the higher N:P2O5 ratios was likely due to the number of boils (Figure 2). Increasing the N:P2O5 ratios did increase boll size (Figure 3). Increased boll size was a function of higher micronaire, owing to more mature fibers in the bolls (Figure 4). Methodology Location. The study was conducted at the Crop Production Research Lab in Terry County, TX on an Amarillo loamy fine sand (fine-loamy, mixed, superactive, thermic Aridic Paleustalf). Irrigation. The center pivot was equipped with LEPA application technology and nozzled to apply 2, 3 and 5 GPM/A, which corresponds with 33, 50, and 90 percent PET replacement, respectively. These water supplies represent the irrigation capabilities found throughout the Southern High Plains region. Irrigation was on a five-day schedule and adjustments were made according to rainfall to meet the crop water requirements. Application method. The four application methods used included a no P control, preplant, sidedress, and fertigation. Preplant N:P205 was banded with a sweep rig four weeks prior to planting. The sidedress N:P205 was banded with a sweep rig and split into three equal applications at preplant, first square, and first flower. Fertigation was applied at least four times starting at first square and continuing through peak bloom. All treatments received 100 lbs/A N through the irrigation water. The preplant, sidedress, and fertigation plots received 40 lbs/A P2O5. N:P2O5 ratios. The N:P2O5 ratios were 5:0, 5:1, 5:2, and 5:3 (lbs of N:lbs P2O5) per inch of total water. The 5:0 received only N. The 5:2 ratio supplied 40 lbs/A P2O5 in the 5 GPM/A water supply, which is the standard recommendation in the area. Each water supply received a different amount of N and P based on total water applied throughout the season. Yield determination. Cotton development and boll distribution was monitored during the season by plant mapping at first flower, peak bloom, and at harvest. Yields were determined by hand harvesting samples and ginned in a plot gin. Lint weight, seed weight, and lint percent were measured and used to calculate yield. Fiber samples were taken for fiber quality measurements at the International Textile Center in Lubbock, TX. Reiter is a Graduate Research Assistant and Dr. Krieg is a professor in the Plant and Soil Science Department at Texas
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