Agronomic Performance of Cropping Systems with Contrasting Crop Rotations and External Inputs.

Cropping systems with less reliance on external inputs could improve agricultural sustainability if they can produce high and consistent crop yields over time. A 17-yr field experiment was conducted in southwestern Minnesota to evaluate the effects of zero-external-input (ZEI), low-external-input (LEI), high-external-input (HEI), and organic-input (OI) cropping systems on crop yield, yield variability, and yield stability over time in a 2-yr soybean [Glycine max (L.) Merr.]-corn (Zea mays L.) rotation and a 4-yr oat (Avena sativa L.)/alfalfa (Medicago sativa L.)-alfalfa-corn-soybean rotation. Across years, corn grain yield was 14 to 40% greater with the 4-yr crop rotation than the 2-yr crop rotation in the ZEI, LEI, and OI systems, but was similar between crop rotations in the HEI system. Within the 4-yr crop rotation, corn grain yield did not differ among the LEI, HEI, and OI systems, and was 77 to 89% greater than that with the ZEI system. However, with the 2-yr crop rotation, yield was highest with the HEI system, lowest with the ZEI system, and intermediate with the LEI and OI systems. Across cropping systems, the 4-yr rotation increased soybean yield by 8% and reduced variability in corn and soybean yields. With the HEI system, oat, corn, and soybean yields were among the highest and least variable compared to the ZEI, LEI, and OI systems, but yield and yield variability for oat and alfalfa were similar between the HEI and LEI systems. Alfalfa yields were highest, least variable, and most stable with the OI system, while oat yield was similar with the OI and HEI systems. These results demonstrate the importance of extended crop rotations with forage legumes for corn and soybean production in reduced-input systems, and that long-term productivity of oat, alfalfa, and corn can be maintained with organic management.