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 yr–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.