Submitted to: Better Crops
Publication Type: Popular Publication
Publication Acceptance Date: January 19, 2001
Publication Date: February 1, 2001
Citation: Halvorson, A.D., Reule, C.A. 2001. Multiple year response of irrigated winter wheat to a single application of phosporus. Better Crops. 85(1): 14-17. Interpretive Summary: Soil phosphorus (P) deficiency for winter wheat is common in the central Great Plains. In this study, we evaluated the response of continuous winter wheat to P and N fertilization within a reduced-till/no-till production system under limited irrigation. Fertilizer P (0, 69, and 137 lb P2O5/a) was applied only one time, just prior to planting a fourth winter wheat crop on a Weld silt loam soil with a low soil test P level. Fertilizer N rates of 0, 50, 100, 200, and 300 lb/A were also established as subplots within each P rate, however, they were reduced for the fifth and sixth crops to 0, 30, 60, 120, and 240 lb N/a. Grain yields were increased each year by N and P treatments. Both N and P fertilization were needed to optimize grain yield. The 69 lb/a P2O5 rate resulted in a greater 3-year yield increase than with the 137 lb/a P2O5 rate at the lower N rates. As the total N applied increased, the 137 lb/a P2O5 rate was needed to maximize yield potential. The 3-year grain yields were near maximum with the total application of 220 lb N/a and 137 lb P2O5/a. The economic returns show that P fertilization optimized grain yields and net return to N fertilization. Without N fertilization, the P applications were not profitable the first crop year. Application of P also improved N use efficiency. Residual soil nitrate-N levels after harvest of the last crop were lower with than without P fertilization. The results from this study demonstrate that a single P fertilization can influence grain yields and economic returns for several years. The results show that a balanced N and P fertilization program is needed to optimize yields and economic returns and reduce the potential for NO3-N contamination of groundwater.
Technical Abstract: Information on multiple year responses of irrigated winter wheat to a single application of P fertilizer in the Central Great Plains is limited. The effect of one-time P applications (0, 69, and 137 lb P2O5/A), with 5 N rates applied annually as subplots, on winter wheat grain yields, economic returns to fertilizer, and residual soil N was studied. Winter wheat was grown on the same plots for 6 consecutive years under limited irrigation o a Weld silt loam soil. Single P applications applied just prior to planting the fourth wheat crop significantly increased grain yields each of the three following consecutive years. Applying N to P fertilized plots resulted in greater yields and economic returns than when N or P was applied alone. The 137 lb P2O5 plus 120 lb N/a treatment produced 80 bu/a more grain in 3 crops than without P and N applied. Soil test P and residual NO3-N levels were significantly increased by P and N fertilizer additions, respectively. Soil NO3-N in the 0-6 ft depth for the highest N rate was 687 lb N/a without P and 409 lb N/a with 137 lb P2O5/a applied. Downy brome infestations also responded positively to N and P fertilization in this monoculture winter wheat system. The results from this study demonstrate that a single P fertilization can influence grain yields and economic returns for several years. Therefore, the cost of fertilizer P applications should probably be amortized over several years. The results show that a balanced N and P fertilization program is needed to optimize yields and economic returns and reduce the potential for NO3-N contamination of groundwater.