Fertilizer N Equivalence of Alfalfa, Birdsfoot Trefoil, and Red Clover for Succeeding Corn Crops

A 6‐yr field experiment was conducted in central Pennsylvania to determine the fertilizer N equivalent value of three forage legumes managed as hay prior to 3 yr of succeeding corn ( Zea mays L.). The forage component of the rotations were 3 yr of alfalfa ( Medicago sativa L.), 3 yr of birdsfoot trefoil ( Lotus corniculatus L.) (BFT), and 2 yr of red clover ( Trifolium pretense L.). There was no significant grain yield response to N fertilizer for first‐year corn following any of the legumes. The 3‐yr total fertilizer N equivalences of alfalfa, BFT, and red clover were estimated to be 167,151, and 131 lb/acre, respectively. The proportion contributed each year averaged 70% the first, 20% the second, and 10% the third for alfalfa and red clover, and 55%, 30%, and 15% for the three years with BFT. The beneficial effect of legumes on subsequent corn yields appeared to be due primarily to their residual N rather than to a crop sequence or rotation effect.