On-Farm Assessment of Rotation Impact on High-Yield Irrigated Maize.

Yield advantage of growing maize in rotation with soybean, compared with continuous maize, has been extensively reported for rainfed environments based mostly on data collected in experiments conducted at research plots. The objective of this study was to investigate (1) on-farm rotation yield impact on high-yield soybean-maize irrigated crop systems in Nebraska (western US Corn Belt), and (ii) variation in rotation impact across year, regions, and management practices. We used a database on yield and applied inputs collected from irrigated maize and soybean fields in three regions of Nebraska (Tri-Basin, Central Platte, and Lower Niobrara) from 2005 to 2013. The database contained >3000 field observations per year. Absolute (and relative) difference in mean annual yield of maize after soybean versus continuous maize ranged from 0.6 Mg ha^-1 (5%) to 0.2 Mg ha^-1 (2%) across regions. Interestingly, rotation effect was consistent across years only in Tri-Basin, which is the region with relatively high and homogenous soil principal component scores (a proxy to soil quality). Significant rotation x nitrogen (N) fertilizer rate interaction was found in Central Platte, suggesting that rotation yield impact depends on the level of N fertilization. Indeed, rotation effect was greater at low N fertilizer rates. Rotation x soil principal component score interaction was significant in Lower Niobrara, suggesting that soil quality plays an influential role in determining magnitude of rotation effect. Rotation effect was not affected by change in maize sowing date but increased with increasing yield of previous maize crop. These results suggest that, in good and uniform soils, rotation effect is consistent across years. In contrast, the rotation effect is more erratic in regions with heterogeneous soils or poor quality soils. Nitrogen fertilizer and residue from previous maize crop seems also to play a role at determining magnitude of yield advantage with rotation.