Long-Term Impacts of Cropping Systems and Landscape Positions on Grain Crop Production on Claypan Soils.

Sustainable grain crop production on vulnerable claypan soils requires improved knowledge of long-term impacts of conservation cropping systems (CS) with reduced inputs. Therefore, effects of CS and landscape positions (LP) on corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) yield, yield stability, and yield variability were evaluated from 1991 to 2010 on a claypan soil near Centralia, MO. Replicated treatments were three CS (2-yr mulch till corn-soybean [MTCS], 2-yr no-till corn-soybean [NTCS], and 3-yr no-till corn-soybean-wheat-cover crop [NTCSW]) and three LP (summit, backslope, and footslope). Corn yield was equivalent among systems on the summit, was 13% higher for the no-till systems on the backslope, and was 14% lower for NTCSW on the footslope than other systems. Soybean yield was 8% higher on the summit and 24% higher on the backslope in both no-till systems and 12% higher on the footslope in NTCSW than MTCS. Regression stability analysis showed that corn yield was more stable (i.e., less yield change as environmental conditions changed) in NTCS and NTCSW than MTCS, and that stability increased from the footslope to summit. Soybean yield was less stable in both conservation CS than MTCS and the effects of LP on stability were similar to corn. The coefficient of variation (CV) of corn yield across years was 10 percentage points lower in NTCS and on the footslope, and of soybean yield was 10 percentage points lower at the footslope and summit. Wheat production was not affected by LP. Results indicate that conservation systems often can maintain grain crop productivity equal to, increase yield stability above, and reduce yield variability below those of a conventional system (MTCS) on claypan soils.