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Fluid Journal : Fluid Journal 1999-2001
1 Fluid Journal Spring 2000 Summary: Multiple phosphorus applications in a complete nutrient mixture, including nitrogen (N) and sulfur (S) applied through center pivots using the LEPA mode, resulted in greater cotton yields than a single preplant application or split applications using sidedressing. The yield increase was due to a combination of greater fruit production and retention and larger fruit size (lint per boll). The 5:1 N:P2O5 ratio optimized lint yields while using less P fertilizer. Increasing N:P2O5 ratios from 5:1 to 5:3 resulted in a linear increase in lint per boll due to increased fiber mass per unit length (micronaire). Fertigation of complete N:P:S nutrient blends offers the irrigated cotton producer the flexibility to apply fertilizer based on yield potential and crop development stage. Increasing use of conservation tillage has resulted in greater usage of granular P-based fertilizer broadcast several months prior to planting cotton. The calcareous nature of Southern High Plains soils presents a major problem with P availability due to high pH (7.4 to 8.0) and the abundance of CaCO3. often at the soil surface. Under these conditions, Ca-P complexes rapidly form, reducing the availability of soluble P for plant use. Cotton yields on the Texas High Plains are limited first by water supply. The seasonal rainfall provides only 50 by J.S. Reiter and Dr. D. R. Krieg Cotton Yields Respond To Phosphorus Fertigation Texas research shows fertigation is a viable option to save cotton growers both time and money on fertilizer inputs. percent or less of the crop water requirement for maximum yield within the constraints of the growing season. When irrigation is used to supplement rainfall, nutrient supply becomes the next limiting factor, with N supply being of major importance. Previous research sponsored by the FFF has demonstrated the optimum water-to- nitrogen ratio for maximizing yields and maintaining lint quality. For each inch of total water available during the growing season, 5 lbs. of N are required to maximize water-use efficiency. Applying N through irrigation water at therateof10lbs.ofNperinchof irrigation water to account for rainfall (50% of available water) is the ideal approach and offers flexibility in management based on crop yield potential. Yield potential is largely a function of growing season length Figure 1. Effect of N:P2O5 ratio on lint yield, Reiter, et al., Texas Tech University, 1999. Figure 2. Effect of N:P2O5 ratio on boll number Reiter, et al., Texas Tech University, 1999.
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