Yield and water-use efficiency of eight wheat cultivars planted on seven dates in northeastern Oregon

Wheat (Triticum aestivum L.) yields in the inland Pacific Northwest are limited by inadequate water supply late in the growing season. Choosing a suitable planting date and genotype with the appropriate phenology that matches crop growth to the water supply will produce optimum grain yields. The objectives of this study were to investigate the effects of (i) planting and (ii) wheat genotype differences on grain yield, evapotranspiration (ET), and water-use efficiency (WUE). A 3-yr experiment was conducted on a Walla Walla silt loam (coarsesilty, mixed, mesic Typic Haploxeroll) near Pendleton, OR. Six winter and two spring wheat cultivars were planted in seven planting treatments (planting practices that include planting date, seeding rate, drill type, row space, and seeding depth). Soil water content was measured to determine ET. Planting treatments greatly influenced winter wheat yield. Different winter wheat cultivars responded differently to planting treatments. The optimum yield was produced at October plantings for all cultivars. Yield from September plantings was 745 to 1550 kg ha(-1) less than that from the October plantings, and yield also decreased when planting was delayed beyond October. For spring wheat, effect of planting treatments on yield was not statistically significant and there was no significant cultivar effect. Planting treatments significantly affected ET after adjusting for vapor pressure deficit (ET/ VPD). Winter and spring wheat planted in the spring had approximately 380 to 650 mm kPa(-1) less ET/VPD (approximately 110-160 mm ET) than that planted in the fall. However, WUE was not significantly affected by planting treatments and cultivars.