Comparative Response of Soybeans and Corn to Phosphorus and Potassium 1

Much interest has developed concerning the comparative responses of soybeans [ Glycine max (L.) Merr.] and corn ( Zea mays L.) to fertilization. Grain yields of soybeans and corn grown side by side and in response to direct and residual P and K fertilizer applications were compared on an energy basis over 4 years of field experimentation. Corn was significantly more responsive than soybeans to direct and residual fertilizer P and to direct application of K. Limited nutritional requirements of soybeans were indicated by the small response from applied P and K fertilizers on land of low fertility, by the lack of response to more than a maintenance rate of P application, and by the fact that soybeans did not respond appreciably to a second cycle of P and K fertilization although the soil remained low in P and low to medium in K. The corn responded to the second increment of P and to a second cycle of P fertilization. Soybeans showed little difference between the effect of direct and residual fertilizer on yield. Corn responded to K in the year of application, but not to residual fertilizer. Differential response of corn from direct and residual P application was dependent on seasonal conditions. In the corn‐soybean cropping sequence on Webster silty clay loam where direct response from fertilizers occurred, P and K applications in alternate years were more effective for corn than for soybeans. The advantage of corn fertilization was relatively insensitive to soybean/corn price ratios.