Multiple‐Year Response of Winter Wheat to a Single Application of Phosphorus Fertilizer

Information on multiple‐year responses of irrigated winter wheat ( Triticum aestivum L.) to a single application of P fertilizer in the central Great Plains is limited. The effects of one‐time P applications (0, 34, 67 kg ha −1 ), with 5 N rates applied annually as subplots, on winter wheat grain yield and protein were studied. Winter wheat was grown on the same plots for three consecutive years under limited irrigation on a Weld silt loam (fine, montmorillonitic, mesic Aridic Paleustoll). Single P applications in the fall of 1983 significantly increased grain yields each of three consecutive years. Applying N to P‐fertilized plots resulted in greater yields than when N or P was applied alone. The 67 kg P plus 134 kg N ha −1 treatment produced 5405 kg/ha more grain in three crops than without P and N applied. Grain protein was reduced by P fertilization at low N rates, but increased by N fertilization. Soil‐test P and residual NO 3 ‐N levels were significantly increased by P and N fertilizer additions, respectively. Soil NO 3 ‐N in the 0 to 180‐cm depth for the highest N rate (336 kg N ha −1 in 1984 and 268 kg N ha −1 in 1985–86) was 764 kg N ha −1 without P and 458 kg N ha −1 with 67 kg P ha −1 applied. Downy brome ( Bromus tectorum ) infestations responded positively to N and P fertilization and tended to increase in severity each year in this monoculture winter wheat system. The results indicate that an adequate level of P and optimum level of N are needed to achieve efficient use of these nutrients by winter wheat and to reduce the amount of potentially leachable NO 3 ‐N in the soil profile.