Crop Diversification and Management System Influence Yield and Weeds in the Northern Great Plains.

Available water, depleted soil quality, and weed competition are major constraints to dryland crop production in the northern Great Plains.  We initiated a trial in 2004 comparing four crop rotations, with each rotational 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, SW-barley hay-corn-pea.  Ecological management practices vary by crop, and are designed to improve crop competitiveness with weeds and snow capture.  After three years, the main effects of rotation and management system were significant for grain yield of pea and SW.  SW yield increased when produced in a two-year rotation with pea, but additional yield was not gained by less frequent planting than every other year.  Pea yield was greater following barley hay or corn than when following spring wheat.  Hay production of barley was greater under ecological than conventional management.  Ecological management and increased diversification reduced weed density and biomass in SW and pea at harvest.  Tillage system did not impact crop yield or weed biomass.  Early results from this long-term study indicate that diversified rotations improve spring wheat and pea yield, in part through decreased weed density.  Pea and barley hay competitiveness with weeds was improved with ecological management.