Wheat - Cropping systems research in the world's driest rainfed wheat region

Winter wheat (Triticum aestivum L.)-summer fallow (WW-SF) is the predominant cropping system in the 120 000-ha Horse Heaven Hills (HHH) region in south-central Washington, USA. Blowing dust from residue- and roughness-deficient SF results in soil loss and causes health problems. Annual no-till cropping to replace SF would provide year-round protection against wind erosion. A 6-yr field study was conducted from 1996 to 2002 to evaluate the agronomic and economic feasibility of continuous annual no-till hard red spring wheat (HRSW) as an alternative to traditional WW-SF. Long-term average annual precipitation at the experiment site is 152 mm, which we believe is the lowest for any nonirrigated wheat region of the world. Annual precipitation during the study ranged from 111 to 240 mm and averaged 153 mm, with two wet years followed by a 4-yr drought. Russian thistle (Salsola iberica Sennen and Pau) heavily infested HRSW plots and depleted soil water during the two wet years. Seed-zone water content in SF was sufficient to plant WW in late August in only 2 of 6 yr. Mean (6-yr) grain yield was 1190 kg ha(-1) for WW-SF (one crop every 2 yr) and 530 kg ha(-1) for annual no-till HRSW. The number of kernels per spike had a significant contribution to yield during years of acute water stress. Net economic returns for annual HRSW lagged WW-SF by an average $95 ha(-1) yr(-1). Although continuous annual no-till cropping has clear environmental advantages, it is not economically competitive with WW-SF with current technology in the HHH.