Tillage Method and Sowing Rate Relations for Dryland Spring Wheat, Barley, and Oat

Some farmers in the Inland Pacific Northwest have reported a lower grain yield of spring cereals with no-till (NT) compared to conservation tillage (CT). A 4-Y field study was conducted in a 12-in annual precipitation zone to determine tillage method and sowing rate effects on seed-zone water, seed-zone temperature, plant stand, grain yield, grain yield components, and straw production for three spring-sown cereal species. Wheat, barley, and oat were sown at 120, 200, and 280 seeds/m2 (about 44, 72, and 100 lb/ac) in a split plot design with NT and CT as main plots and sowing rate by cereal species combinations as subplots. Factors other than tillage method (i.e., drill, sowing date, fertilizer rate, sowing depth) were held constant. There were no differences in plant stand between NT and CT, but grain yield was reduced by 5 % in NT partly due to less water in the seed zone compared to CT during early plant development. Disruption of capillary continuity with CT appeared to restrict upward movement of water, resulting in greater retention of water in the seed zone underlying the depth of tillage. Grain yield was not affected by the sowing rate for any crop species because increased number of heads per unit area (HPU) and kernels per head (KPH) consistently compensated for reduced plant stand density. With precise seed placement, the sowing rate of spring cereals can be reduced by 50 % or more from rates commonly used. Abbreviations: C, crop species; CT, conservation tillage; DWP, days without precipitation; HPU, heads per unit area; KPH, kernels per head; KW, kernel weight; NT, no-till; PNW, Pacific Northwest; R, sowing rate; T, tillage method; WUE, water use efficiency; WW-SF, winter wheat–summer fallow; Y, year. Acknowledgements: The authors thank Donald Wellsandt who provided land