Environmental concerns in conjunction with the rising cost of fertilizer have created a strong incentive for corn producers to accurately assess N requirements and improve fertilizer efficiency. The objective of this study was to determine if N fertilizer rate can be decreased, while maintaining yield, when 1^st-year corn was grown after a leguminous cover crop in a four year rotation (corn-corn-soybean-wheat). Using data from a long term research trial established in 1993 at the W.K. Kellogg Biological Station, Hickory Corners, MI, we compared the presence vs. absence of red clover following wheat on soil N fertility as indicated by the pre-sidedress soil N test (PSNT). The experimental design consisted of split plots containing cover and no cover crop with four replicates. In addition, the design accommodated every phase of the four year rotation each year, which allowed evaluation of N budgets for four complete rotations from 1995 through 2001. The PSNT was conducted in June and fertilizer rates were adjusted according to Tri State Fertilizer Recommendations. Fertilizer N rate was reduced on average by 39% (130 vs. 101 kg ha^-1) when 1^st year corn followed red clover compared with no cover crop, while grain yields were similar, averaging 6.9 vs. 7.1 Mg ha^-1. The reduction in fertilizer N rate as determined by PSNT was assumed to equal the amount of N released from red clover, and improved fertilizer N use efficiency by 35% (defined here as yield divided by fertilizer N rate). Overall, these results suggest that home-grown N in the form of red clover can be substituted for fertilizer N, improving efficiency while maintaining yield of corn.