| The efficient management of both water and nitrogen (N) is critical to reducing the accumulation of nitrate-nitrogen (NO{dollar}sb3{dollar}-N) in ground water under much of the Central Platte River Valley of Nebraska. Overly optimistic yield goals and the failure to account for residual inorganic soil N, N mineralization, and N supplied by irrigation water contribute to overfertilization and the potential for nitrate leaching. In order to evaluate the N uptake efficiency of NO{dollar}sb3sp-{dollar} applied with irrigation water and to determine the fate of fertilizer and irrigation applied N, a 2-year study on irrigated corn (Zea mays L.) was initiated in Hall County, Nebraska. Microplots were established to accommodate 4 fertilizer N rates (0, 50, 100, and 150 kg/ha) receiving irrigation water containing 3 levels of NO{dollar}sb3{dollar}-N (0, 10, 20 mg/L). For each given treatment, stable isotope {dollar}sp{lcub}15{rcub}{dollar}N was applied as a tracer in either the fertilizer or water.; Grain yields in 1982 were not influenced by fertilizer N rates or irrigation NO{dollar}sb3{dollar}-N concentrations. Stover yield and percent N in both grain and stover were positively correlated to fertilizer N rate. The lack of grain yield response is attributed to the relatively high level of residual soil N and the high amount of mineralized N. During the second year, a more typical N response was obtained with the maximum grain yield reached at the 100 kg N/ha fertilizer rate. Under the conditions of this study, the majority of N supplied with irrigation water was applied after tasseling which was too late to affect grain yields. For both years, the uptake efficiency of the sidedressed N fertilizer was not affected by the application of N in the irrigation water. The N uptake efficiency of the NO{dollar}sb3sp-{dollar} applied in the irrigation water was negatively correlated to the amount of sidedressed fertilizer N. Second year recovery of residual {dollar}sp{lcub}15{rcub}{dollar}N applied in the irrigation water was greater at the highest rates of fertilizer and irrigation N. Both growing seasons ended with substantial amounts of residual NO{dollar}sb3sp-{dollar} in the soil derived from mineralization. Production practices must be developed which will make greater use of this late season mineralized N. |
