Evaluation of the allelopathic effects of redroot pigweed (Amaranthus retroflexus L.) and wheat (Triticum aestivum L. cv. Pishgam)plants on growth parameters of each other in intercropping

Weeds cause a number of harms in agro-ecosystems. Allelopathy refers to the beneficial or harmful effects of one plant on another by the release of inhibitory substances from plants into the environment through root exudation, leaching, volatilization, and through the decomposition of plant residues. In order to study the allelopathic effects of different wheat/redroot pigweed densities on growth parameters of each other, an experiment was conducted at five levels of density with ratios of ۱۰۰ to ۰, ۰ to ۱۰۰, ۵۰ to ۵۰, ۷۵ to ۲۵ and ۲۵ to ۷۵ wheat to redroot pigweed with three replications under laboratory condition. Chlorophyll assay was performed by Wellburn and Lichtenthaler (۱۹۸۳). Results showed that with increasing redroot pigweed density in the ratio of ۲۵ to ۷۵ wheat to redroot pigweed, fresh weight of root and shoot, root and shoot dry weight and shoot length decreased significantly in wheat and root length of wheat increased significantly. In equal ratios of wheat and redroot pigweed, root dry weight and length of shoot increased significantly in redroot pigweed and with increasing density of wheat, a significant reduction in redroot pigweed root length was observed. In redroot pigweed with increasing redroot pigweed density, both of chlorophyll a and b as well as total chlorophyll increased significantly and with increasing wheat density in the ratio of ۷۵ to ۲۵ wheat to redroot pigweed, chlorophyll a and total chlorophyll of redroot pigweed showed a significant decrease. In wheat, there was a significant decrease in chlorophyll a in the ratio of ۷۵ to ۲۵ wheat to redroot pigweed. This study showed that by increasing wheat density, the allelopathic effects of redroot pigweed can be reduced by reducing the effect of released toxins.