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Fluid Journal : Fluid Journal 2002-2004
Spring 2004 Will Continuous Supply of NH4+ -N Increase Irrigated Crop Production? Dr. D. R. Krieg Summary: Purpose of this project was to determine if maintaining a relatively high supply of ammoniacal nitrogen (NH4+-N) throughout the major demand period of agronomic crops would reduce the biological cost of nitrogen (N) acquisition and reduction, allowing more of the daily photosynthate to be used for growth. Results obtained from our studies supported this hypothesis in the case of cotton but not for sorghum. The two species differ in photosynthetic systems with the C-4 system of sorghum being more effective than the C-3 of cotton. The two species also differ in N concentration per unit of dry matter production with cotton being higher than grain sorghum. Fertigating a majority of the crop N requirements makes good sense. Providing the proper NH4+:NO3- ratio for the most efficient use of N supply also increased yield and the efficient use of both water and N, the two most expensive inputs of irrigated agriculture. Results of studies in the Texas South Plains showed positive responses with cotton but not sorghum. Fluid Journal 1 Specific objectives of this project included: • Determining growth, yield, and quality of several crop species differing in chemical composition as a function of NH4+:NO3- ratios in the fertilizer solutions applied with each increment of irrigation water (center pivot). • Determining N and water use efficiency as a function of both water supply & N form in the water. 100/0 75/25 50/50 25/75 0/100 3 GPMA 4 GPMA 5 GPMA 0 200 400 600 800 1000 1200 1400 1600 1800 LINT YIELD (Pounds/Acre) NITROGEN SOURCE (NH4:NO3 RATIOS) 100/0 75/25 50/50 25/75 0/100 3 GPMA 4 GPMA 5 GPMA 0 1000 2000 3000 4000 5000 6000 7000 GRAIN YIELD (Pounds/Acre) Figure 1. Lint yield response to N source in Texas South Plain studies, 2001-2002. Figure 2. Grain sorghum yield response to N sourcein Texas South Plain studies, 2001-2002. GPMA = gallons per minute per acre.
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