Diversifying Spring Wheat Production Systems Influences Weed Community.

Weed competition constrains dryland crop production in the northern Great Plains.  We initiated a field trial in 2004 comparing four crop rotations, with each component in a two-by-two matrix of tillage (conventional vs. zero tillage) and management (conventional vs. ecological) systems.  Rotations are continuous spring wheat (SW), SW-pea, SW-barley hay-pea, and SW-barley hay-corn-pea.  Ecological management practices vary by crop and are designed to improve competitiveness with weeds and snow capture.  Over five years, the three-year rotation had lower densities of green foxtail, kochia, and total weeds prior to herbicide application.  Across rotations, densities of wild oat, green foxtail, and total weeds were greater under conventional management than ecological management before herbicide application and at harvest.  Spring wheat in diversified rotations had lower density of wild oat, green foxtail, kochia, and total weeds than did continuous spring wheat.  Ecological management and diversified rotations improved weed management under semi-arid conditions.