Weed community responses in a corn-soybean intercrop

. Weed community responses were examined in a corn-soybean intercrop in southwestern Michigan, USA, with and without nitrogen fertilization. Weed suppression was observed when intercropping was additive, but the depression in above-ground weed biomass was not due to a synergistic effect of crop diversity, but rather to the effects of crop density and identity. Intercropping did not have a greater suppressive effect than monocrops on weed biomass in a replacement intercrop when crop densities were similar to those in monocultures. Similarly, intercropping per se did not alter the diversity, species richness or composition of the weed community. The presence and density of corn was more important in affecting the weed community than was the density of soybeans or than intercropping itself. Fertilization and the interaction between fertilization and crop type had few effects on the weed community.