Comparison of Fallow Tillage Methods in the Intermediate Rainfall Inland Pacific Northwest

Winter wheat (Triticum aestivum L.) is usually grown in the Pacific Northwest (PNW) intermediate rainfall zone following tilled or chemical summer fallow. Studies were conducted near Davenport, WA and Helix, OR over two fallow winter wheat cycles to evaluate the efficacy of reduced or no-tillage fallow compared to conventional fallow and compare the efficacy of herbicides applied using a light-activated sensor-controlled (LASC) applicator to broadcast applications. Six treatments included conventional primary tillage followed by rodweeding; sweep-tillage followed by rodweeding, broadcast, or LASC herbicide application; and no-tillage followed by broadcast or LASC herbicide application. Broadcast and LASC herbicide applications controlled weeds similarly in no-tillage treatments. However, LASC applications used from 45 to 70% less herbicide than broadcast applications to attain similar weed control. No-tillage or sweep-tillage systems with herbicide application had from 15 to 30% greater surface residue cover than the conventional tillage system. Available soil moisture in both the root-zone and seed-zone soil profiles at time of planting was similar among tillage systems. There were no differences in wheat quality parameters across treatments. The conventional tillage system had similar wheat grain yield as sweep-tillage systems followed by rodweed or broadcast herbicide application, but yields were up to 21% greater than sweep-tillage with LASC applied herbicides and no-tillage systems. Reduced tillage systems using sweep-tillage and broadcast herbicide application could potentially replace more tillage intensive fallow systems in the PNW.