Browsing by Author "Scharf, Peter C."
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- Development of field-specific spring N rate recommendations for winter wheatScharf, Peter C. (Virginia Tech, 1993)Optimum spring N fertilizer rates for winter wheat in Virginia vary widely from field to field, but traditionally spring N is applied at a uniform rate to all fields. A recently-developed tissue test procedure provides a field-specific evaluation of crop N status and predicts optimum N rate for the second spring N application in a split spring application management system. However, this procedure is based on a small number of researcher-planted experiments utilizing a single cultivar; it fails to provide field-specific rate recommendations for the first spring N application; and it is not accessible to farmers who are unwilling to split their spring N applications. Our objectives were: to evaluate the reliability of the tissue test procedure in a large number of farmer fields; to develop a method for making field-specific N rate recommendations for the first spring application in a split-application management system; and to develop a method for making field-specific N rate recommendations in a single-application management system. Forty-five spring N rate experiments were established in farmer fields over a five-year period. A range of N fertilizer rates was applied in early spring (Zadoks growth stage 25) and again in mid-spring (Zadoks growth stage 30) in all possible combinations. Yield data were used to calculate economic optimum N rates at growth stage (GS) 25 and GS 30 with split-application management, and at GS 25 with single-application management. These optima were regressed against a variety of predictor variables measured in the same fields. The reliability of the previously-developed tissue test procedure for making GS 30 N rate recommendations was confirmed. Tiller density was the best predictor of optimum GS 25 N rate with split-application management, while soil nitrate to 90 cm was the best predictor of optimum GS 25 N rate with single-application management. These three relationships fit together to form a flexible and powerful system for making spring N rate recommendations for winter wheat. This system increased estimated profit and apparent fertilizer efficiency in these experiments.
- Nitrogen loss inhibitors in intensively managed winter wheatScharf, Peter C. (Virginia Polytechnic Institute and State University, 1988)Several potential pathways exist for significant nitrogen loss from nitrogen fertilizer applied to winter wheat in Virginia. A number of materials have been previously identified which inhibit steps in one or more of these loss pathways. Ammonium polyphosphate, ammonium thiosulfate, dicyandiamide, potassium chloride, and monoammonium phosphate were chosen for use in the present study. They were mixed, singly and in combinations, with UAN solution or urea solution and spring top-dressed on soft red winter wheat. Experiments were conducted over two growing seasons at two locations each season. Nitrogen uptake was measured in mid-season and yield measured at harvest. In the second season, field measurement of ammonia volatilization was performed in the experiment utilizing urea solution. Addition of monoammonium phosphate significantly reduced volatilization from urea solution applied to winter wheat at both locations; however, weather conditions were such that total volatilization was low in this season, and the reduced losses were not reflected in increased nitrogen uptake or yield. None of the treatments significantly increased yield in any experiment, nor consistently increased mid-season nitrogen uptake.
- Nitrogen Management for Winter Wheat: Principles and RecommendationsAlley, Marcus M.; Scharf, Peter C.; Brann, Daniel E.; Baethgen, Walter E.; Hammons, J. L.; Thomason, Wade E. (Virginia Cooperative Extension, 2019-03-20)Discusses the use of nitrogen fertilizers for winter wheat and makes recommendations for when and how much nitrogen fertilizer to use.
- Nitrogen Management for Winter Wheat: Principles and RecommendationsAlley, Marcus M.; Scharf, Peter C.; Brann, Daniel Edward; Baethgen, Walter E.; Hammons, J. L. (Virginia Cooperative Extension, 2009)Discusses the use of nitrogen fertilizers for Winter Wheat and makes recommendations for when and how much nitrogen fertilizers to use.
- Nitrogen Management for Winter Wheat: Principles and RecommendationsAlley, Marcus M.; Scharf, Peter C.; Brann, Daniel Edward; Baethgen, Walter E.; Hammons, J. L. (Virginia Cooperative Extension, 2019-01-23)Discusses the use of nitrogen fertilizers for Winter Wheat and makes recommendations for when and how much nitrogen fertilizer to use.