Development of field-specific spring N rate recommendations for winter wheat

dc.contributor.authorScharf, Peter C.en
dc.contributor.committeechairAlley, Mark M.en
dc.contributor.committeememberBrann, Daniel E.en
dc.contributor.committeememberDillaha, Theo A.en
dc.contributor.committeememberEvanylo, Greg K.en
dc.contributor.committeememberMartens, David C.en
dc.contributor.committeememberReneau Jr., Raymond B.en
dc.contributor.departmentCrop and Soil Environmental Sciencesen
dc.description.abstractOptimum 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.en
dc.description.degreePh. D.en
dc.format.extentxii, 226 leavesen
dc.publisherVirginia Techen
dc.relation.isformatofOCLC# 28529023en
dc.rightsIn Copyrighten
dc.subject.lccLD5655.V856 1993.S337en
dc.subject.lcshNitrogen fertilizers -- Virginiaen
dc.subject.lcshWinter wheat -- Virginiaen
dc.titleDevelopment of field-specific spring N rate recommendations for winter wheaten
dc.type.dcmitypeTexten and Soil Environmental Sciencesen Polytechnic Institute and State Universityen D.en
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