Slope Position and Grain Yield of Soft White Winter Wheat1

Abstract Winter wheat (Triticum aestivumL.) producers in the Palouse Region of southeastern Washington generally seed one wheat cultivar over a wide range of environmental conditions formed by the rolling topography of the area. A 2‐year field study was conducted during 1977–1979 growing seasons on five slope positions across a Palouse silt loam (fine‐silty mixed, mesic pachic Ultic Haploxerolls), a Naff silt loam (fine‐silty, mixed, mesic Ultic Agrixerolls), and a Snow silt loam (fine‐silty, mixed, mesic Cumulic Haploxerolls) to examine the influence of slope position on grain yield and yield components of 12 soft white winter wheat cultivars. Slope position and cultivar significantly influenced grain yield while only cultivar significantly influenced test weight. There were significant cultivar ✕ slope position and slope position ✕ year interactions for grain yield, test weight, and culm height. Differences in mean grain yield for an individual cultivar ranged from 0.45 to 1.90 Mg/ha when compared across slope positions. Yield components were examined during the 1977–1978 growing season and were found to be significantly influenced by slope position and cultivar. Spikelets/spike and 100‐seed weight were the only yield components to show a significant cultivar ✕ slope position interaction. These findings indicate the need to more clearly define where soft white winter wheat cultivars are best adapted to meet specific environmental and topography conditions.