A MODEL OF THE COMPETITIVE RELATIONSHIPS BETWEEN R-COCHINCHINENSIS AND ZEA-MAYS

An understanding of the competitive relationship between weed and crop can be used in assessing what physiological aspects of the associatio n can be exploited in the control of the weed. Field and greenhouse st udies were conducted with Z. mays L. and Rottboellia cochinchinensis ( Lour.) W D Clayton using a modified replacement series model in which the overall weed crop density in each treatment was maintained as a co nstant, but the proportion of the two species varied. The results indi cated that the crop had greater competitive ability (K(mr)) than the w eed even at increasing weed densities. Under field conditions, the val ues of the Plant Relative Yield (PRY) indicated that severe specific c ompetition was occurring and suggested that some environmental factor was limiting, while the Relative Yield Total (RYT) suggest that either the crop and the weed were exploiting the resources in mutual antagon ism or that allelopathy was occurring. The limiting environmental fact or that both species exploited in mutual antagonism in the field was l ight under conditions of adequate soil moisture and nutrients.