Fertilizer Nitrogen and Residual Nitrate-Nitrogen Effects on Irrigated Corn Yield
A.B. Onken, R.L. Matheson, and D.M. Nesmith
Multirate nitrogen studies were conducted for a 6-yr period, on an irrigated clay loam soil, to determine the influence of applied N and residual soil N on the grain yield of corn (Zea mays L.). Soil samples were taken prior to fertilizer application each year in depth increments of 0 to 0.15, 0.15 to 0.30, 0.30 to 0.60 and 0.60 to 0.90 m and analyzed for nitrate-N (NO3-N). Applied N and residual soil NO3-N were found to significantly influence grain yields. Regression analyses of the data showed highly significant relationships between (i) quantities of NO3-N measured in the upper portions and those measured in the lower portions of the soil profile and (ii) grain yield and applied N and residual NO3-N. Highest coefficients of determination were obtained when residual NO3-N was included as a separate independent variable in the regression equation. Results indicated that residual NO3-N measured to 0.15 m would be sufficient for evaluation of residual N effects on irrigated corn grain yield on this soil. Fertilizer N requirements for several combination of grain yield and residual soil NO3-N were calculated using the N requirement index (NRI) and a power function, and simple and multiple linear response equations generated by regression analysis. A range of values was obtained, with NRI most frequently predicting the highest N requirement. The marginal rate of substitution of residual soil NO3-N for applied fertilizer N was variable and influenced by (i) amount of residual NO3-N, (ii) depth of measurement of residual NO3-N and (iii) maximum grain yield. Fertilizer used efficiency (FUE) was influence by grain yield, fertilizer N rate, and amount of residual soil NO3-N. The greatest reduction in FUE resulted from residual soil NO3-N. In order to maximize FUE, it is necessary to apply the amount of fertilizer N to achieve a given yield level and simultaneously leave as little as possible in the soil to carry over to the next crop year.
Onken, A.B., R.L. Matheson, and D.M. Nesmith. 1985. Fertilizer nitrogen and residual nitrate-nitrogen effects on irrigated corn yield. Soil Sci. Soc. Am. J. 49:134-139.
