Date of Graduation

8-2016

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Richard E. Mason

Committee Member

Trenton L. Roberts

Second Committee Member

Nathan Slaton

Third Committee Member

Lisa S. Wood

Keywords

Biological sciences, Nitrogen fertilizer, Planting dates, Urea, Winter wheat

Abstract

An optimum planting date is important for winter wheat nitrogen (N) management as it dramatically changes the growing environment including temperature and moisture, ultimately affecting fertilizer efficiency and grain yield (GY). In Arkansas, high precipitation in the fall often forces farmers to delay planting and current Arkansas recommendations include the application of fall N when soft red winter wheat (SRWW) is sown later than optimum, despite the lack of data supporting this practice. This study evaluated the effect of rate and timing of N application on GY of SRWW sown at variable planting dates in Arkansas. Granular urea was split applied between the fall (F), late winter (LW) and/or early spring (ES) and compared to N only applied in the spring (LW, or LW + ES). Experiments were conducted at the Newport Research Station (NPRS), Pine Tree Research Station (PTRS), and Rohwer Research Station (RWRS), representing the diverse wheat growing regions in Arkansas. Wheat was sown at three planting dates and supplied with total N rates of 67, 101, 135, 169, and 202 kg N ha-1. Fall-N rates equal to 0, 34, 67 kg N ha-1 were applied after planting at Feekes 3 and spring-N rates equal to 67, 101, 135 and 169 kg N ha-1 were applied at Feekes stage 4 or 5. There was no statistical difference between spring (LW and ES) and split N applications at NPRS where there was low precipitation and the highest residual soil-N and thus decreased potential for volatilization and denitrification. A split fall and spring application was important for maximizing GY on the latest planting date at both PTRS and RWRS and increased mean GY by 1122 and 544 kg ha-1 compared to spring only application, respectively. Overall, results suggest that splitting fertilizer-N between fall and spring has the potential for increasing GY in late-planted wheat in fine-textured soils when there is high precipitation, which favors N loss.

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