Cropping system influence on planting water content and yield of winter wheat

Many dryland producers in the central Great Plains of the USA express concern regarding the effect that elimination of fallow has on soil water content at winter wheat (Triticum aestivum L.) planting and subsequent yields. Our objectives were to quantify cropping system effects (fallow weed control method and crop sequence), including corn (Zea mays L.) (C) and proso millet (Panicum miliacium L.) (M), on soil water at winter wheat planting and subsequent grain yield, and to determine the frequency of environmental conditions which would cause wheat yield to drop below 2500 kg ha(-1) for various cropping systems. Crop rotations evaluated from 1993 through 2001 at Akron, CO, were W-F, W-C-F, W-M-F, and W-C-M (all no-till), and W-F (conventional till). Yields were correlated with soil water at planting: kg ha(-1) = 373.3 + 141.2 X cm (average and wet years); kg ha(-1) = 897.9 + 39.7 X cm (dry years). Increasing cropping intensity to two crops in 3 yr had little effect on water content at wheat planting and subsequent grain yield, while continuous cropping and elimination of fallow reduced soil water at planting by 11.8 cm and yields by 450 to 1650 kg ha(-1), depending on growing season precipitation. No-till systems, which included a 12- to 15-mo fallow period before wheat planting nearly always produced at least 2500 kg ha(-1) of yield under normal to wet conditions, but no cropping system produced 2500 kg ha(-1) under extremely dry conditions.