Economic Comparisons of Crop Rotations Inclluding Alfalfa, Soybean, and Corn

The increasing cost of N fertilizer and development of new alfalfa (Medicugo sativa L.) germplasm with increased storage of reduced N in roots and crowns have accentuated the importance of determining the economic value of 2-yr alfalfa-corn (Zeu muys L.) rotations. Our objectives were to (i) determine the economically optimum rotation/N-fertilization combination of corn following alfalfa at four Minnesota locations and (ii) compare the profitability of alfalfa-corn rotations with that of continuous corn and soybean [Glycine mux (L.) Merr.]-corn systems. Field studies were conducted in 1982 and 1983 at four Minnesota locations (soils were Udorthentic Haploborolls, Typic Haplaquolls, Aquic Haplustolls, and Typic Haplaquolls). Firstyear rotation components included alfalfa, corn, and soybean, and the 2nd-yr component was Corn. Alfalfas were subjected to two harvest systems. Four or five rates of N fertilizer were applied to corn. A linear programming model selected the optimum 2-yr rotation/N-fertilization combination at each location. A parametric procedure was used to determine changes in the optimum rotations as N costs varied ($0.26 to $2.25 kg−1). An alfalfa-corn sequence with alfalfa subjected to a three-cut system was the economically optimum rotation. Continuous corn and soybean-corn systems resulted in at least a $39 and $200 ha−1 decrease, respectively, in 2-yr gross margin. At three of four locations, ‘Saranac AR’ provided greater gross margins than ‘MN ROOT N’, an experimental alfalfa. Optimum rotations were determined more by the quantity and quality of alfalfa forage produced than by differences in second-phase corn grain yield. Our results suggest that management of alfalfa to increase production of high-quality forage will contribute to the economic viability of 2-yr alfalfa-corn rotations.