Weed-crop behaviour in pure and mixed stands of maize and Echinochloa colona link

Abstract

The interference between maize and Echinochloa colona was studied by growing the two species in pure and mixed stands under varied nutritional levels in the soil. Both the species responded to density stress in pure stands by mortality and plasticity. Density dependent mortality was comparatively higher for maize than for E. colona. The higher mortality rate of maize was related to the higher growth rate in this species. The dry matter production was also more sensitive to density stress for maize than for E. colona. The generally higher mortality in the more fertile soil was explained as due to the better expression of genotypic individual differences and the consequent elimination of the weaker individuals by more vigorous ones. In mixed stands, whilst the reciprocal effects of the weed and the crop were brought out due to suitable experimental design, the effect of the weed on the crop was less marked as compared to the reverse effect. This was due to differences in size and growth habit of the two competing species. Whilst the effect of the weed on the crop may be purely a competition by roots for nutrients from the soil the reverse effect could be primarily due to shading of the weed by the crop. The plasticity and mortality responses of the two competing species are discussed and it was shown that: (i) the effect of the weed on the crop was enhanced due to an early start that the former may receive in the mixture and the adverse effect was realized in cob characters and (ii) the interference from the weed to the crop is a continued risk throughout the life cycle and that longer the period of association between the two, greater the damage done to crop yield.