Tracking the Tango Between Tillage, Soil Health, and Weeds: Final Report

This BIOAg project evaluates how reintroducing tillage after long-term no-till affects soil health and weed dynamics in western Washington. Two replicated experiments were established at Washington State University Mount Vernon NWREC in 2021 (Repetition 1) and repeated in 2022 (Repetition 2). Trial 1 compares continued no-till orchardgrass with a one-time spring tillage treatment followed by no-till, measuring bulk density, penetration resistance, gravimetric water content, and field saturated hydraulic conductivity. Trial 2 compares two tillage implement sequences (rototiller vs power harrow) in an annual rotation (kale in year 1; squash in year 2), with similar soil measurements. Soil biology was assessed using PLFA analysis for microbial biomass and community composition. Weed responses were tracked using seedbank sampling (greenhouse grow-out and elutriation), in-season density and biomass, and seed production estimates for common lambsquarters and shepherd’s purse. Results indicate some short-term soil physical changes following one-time tillage and higher weed pressure after tillage in Trial 1, while implement differences in Trial 2 were generally limited.