Crop and weed response to nutrient source, tillage and weed control method in a corn-soybean rotation

The integration of various sustainable management techniques in cropping systems can potentially reduce agro-environmental problems, but may warrant a new approach to weed management, due to changes in weed communities. A 3-yr experiment was conducted to determine the effects and interactions of tillage (moldboard plow or chisel plow), weed control method (chemical or mechanical), and nutrient source (mineral fertilizers or liquid hog manure supplemented with mineral fertilizers) on crops and weeds in a corn (Zea mays L.)-soybean (Glycine mar (L.) Merr.) rotation on two soils (a Sainte-Rosalie clay and a Duravin clay loam, Orthic Gleysols), at Saint-Hyacinthe, Quebec. In most cases, weed density and biomass were more important with mechanical than with chemical control. Nutrient source did not affect weed density, but weed biomass was higher in the manure than the mineral treatment in 1997. Weed populations on both soils were greater with chisel plow tillage combined with mechanical weed control. The presence of crop residues in chisel plow systems may have hindered the efficacy of mechanical weed control operations, particularly when corn was the previous crop. Soybean populations, mid-season biomass and yields were reduced in chisel plow compared with moldboard plow tillage. Corn populations and mid-season biomass were not affected by any of the factors, whereas corn yields showed variable responses over the years. Efficacy of mechanical weed control would need to be enhanced or complemented with other weed control methods, in order to reduce the risks of weed infestations and lower crop yields, particularly in conservation tillage systems. Liquid hog manure would have little effect on weed populations, but would need to be adequately balanced in order to ensure proper crop nutrition and optimum yields.