Corn grain yields and yield stability in four long-term cropping systems

Most long-term studies evaluate only average crop yields and overlook year-to-year yield variability, which could be highly significant. Our objectives were to evaluate the impact of long-term cropping systems and fertility management on corn (Zea mays L.) yield and yield stability. Cropping systems were (i) CC, continuous corn; (ii) CS, corn-soybean [Glycine max (L) Merr.]; (iii) 4C4A, 4 yr corn-4 yr alfalfa (Medicago sativa L.); and (iv) COW2RT, corn-oat (Avena sativa L.)/winter wheat (Triticum aestivum L.)- 2 yr red clover (Trifolium pratense L.)/timothy (Phleum pratense L.). Fertility regimes were inorganic, or manure based on crop N or P requirements. Averaged across fertility regimes, mean corn yields in 4C4A and COW2RT were 10 to 12% higher than CC, and 7% higher in 4C4A than CS. Yield trends were similar (0.28 Mg ha^-1 y ^r-1) among all cropping systems. Coefficient of variation (CV) analysis indicated that yield variability was highest in CC (CV = 28%) and lowest in 4C4A (CV = 21%) across fertility regimes. Regression analysis indicated that response of corn yield to the environment mean did not differ among the cropping systems within inorganic and P-based manure fertility and corn yielded lower in CC than in 4C4A and COW2RT systems. Under N-based manure fertility, yield was lower in CC than in other systems in the poorest-yielding year, but similar in the highest-yielding year. Results suggest that, on average, rotations are likely to produce higher yields than CC across fertility regimes. In high-yielding years with N-based manure fertility, however, corn yield in monoculture may be similar to that in rotations.