Soybean Spatiotemporal Yield and Economic Variability as Affected by Tillage and Crop Rotation

Tillage and crop rotations are practices that influence yields and economic returns. This study was conducted at seven locations in Iowa from 2003 to 2013 with a split-plot design. Tillage systems [no-tillage (NT), strip-tillage (ST), chisel plow (CP), deep rip (DR), and moldboard plow (MP)] were the main treatment and rotations [corn (Zea mays L.)-soybean (Glycine max [L.] Merr.) (C-S), corn-corn-soybean (C-C-S), and continuous corn (C-C)] were the subplot. The objectives were to investigate: (i) annual soybean yield variability, (ii) appropriate tillage systems and crop rotations within location, and (iii) rotation effect on soybean yield and economic returns for the C-S cropping system. Soybean yield varied from 1.5 to 5.0 Mg ha(-1) across Iowa with 21% variability. The yield response to tillage systems at different locations was not significant and the economic return with NT ($1258 ha(-1)) exceeded that with conventional tillage ($1241 ha(-1)). Input costs excluding land rental and crop insurance were lower with NT ($463 ha(-1)) than with conventional tillage ($512 ha(-1)). The C-C-S rotation resulted in greater soybean yields (9%) and economic returns (11%) than the C-S rotation in five out of seven locations. The effect of C-S, C-C-S, and C-C was consistently higher in the southern locations (well-drained soils, warmer temperatures) than northern locations (poorly drained soils, cooler temperatures). Site-specific effects of rotation on soybean yield were greater than tillage system effects. Stable economic returns over time for corn and soybean were more associated with the C-S rotation than with C-C-S and C-C.