Effects of Long‐Term, Annual Applications of N and P on Corn Grain Yields and Soil Chemical Properties1

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Abstract
Maximum yield production in monocultural cropping systems requires annual applications of fertilizer to maintain adequate soil nutrient levels. The rates of applied N and P fertilizers may vary from conservative to excessive applications. Experiments were established at two locations (Ardic Haplustoll and Aridic Argiustoll) to evaluate the effects of annual applications of N and P, over a period of several years, on corn (Zea mays L.) grain yields and the accumulation of these nutrients in the soil. Maximum grain yields were consistently maintained with N applications of 134 to 180 kg/ha and P applications of 20 kg/ha. Applications of N‐rates higher than the optimum resulted in accumulations of residual NO3‐N and subsequent leaching. At one location the soil P level was maintained constant for 21 years with the 20‐kg P rate. A similar trend was observed for the initial 10 years of the second experiment, however, for the last 4 years soil‐P has increased at the rate of 4 ppm annually.

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