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Fluid Journal : Fluid Journal 2002-2004
Fall 2004 Managing Nitrogen With Five-dollar Gas Dr. Gyles Randall Summary: Sound nitrogen (N) fertilizer management practices include applying proper N rates, proper timing, diagnostic tools to assess soil N and plant N status, and the use of nitrifi cation and urease inhibitors, as well as controlled-release N fertilizers. Escalating natural gas prices with little possibility of low-cost nitrogen returning, strongly en- courages growers to fine-tune management practices or jeopardize profits. Fluid Journal 1 The price of N is of concern to many growers because it is one of the highest variable input costs corn farmers encounter. Natural gas, a basic feedstock in the production of N fertilizers, has seen a substantial price escalation within the U.S. in the last few years. Thus the cost of N fertilizer has risen dramatically, giving heightened interest and economic concern to U.S. corn producers. How can N fertilizer be managed more intensely to gain increased efficiency and "greater return for the buck" to American farmers? The following will describe management practices that can be employed now or can likely be used in the future to fine-tune N management, bringing greater return to the grower's pocketbook. These practices generally include applying the correct rate of N, applying N at the proper time to maximize availability and minimize loss, using nitrification and urease inhibitors and controlled release N fertilizer sources if appropriate, and using diagnostic assessment tools to help arrive at the proper N rate (soil N tests, remote sensing, etc.). Proper rate From 1989 through 2001, our recommendations for corn after soybeans were tested on farmers' fields to develop data for validating current recommendations and changing recommendations if needed. Best management practices were used at all sites and are considered essential for efficient N use. Small plots. Thirteen studies conducted from 1989 through 1999 were equally divided between the loess soils (silt loam) of southeastern Minnesota and the glacial till soils (clay loam) of southcentral Minnesota. The plots were 10 to 15 feet wide and 40 to 60 feet long and were replicated four to six times at each site. The farmers tilled, planted, applied pesticides, cultivated, and selected hybrids and planting rates. University scientists applied N fertilizer, hand-harvested the yields, and collected other appropriate field data (weather, past cropping, nutrient history, etc.). N was applied in 30-lb increments at rates from 0 to 180 lbs/A at seven sites and 0 to 150 lbs/A at six sites. Urea was spring preplant applied at 11 sites, and anhydrous ammonia was sidedressed at two sites. The economical optimal N rate (EONR) for each of the sites ranged from alowof0toahighof140lbs/AofN (Figure 1). The EONR averaged across the sites was 86 lbs/A of N while the yield at the EONR (YEONR) was 173 bu/A. Figure 1. Economical optimum N rate (EONR) for 13 small plot sizes in growers' fields in southern Minnesota
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