Integration of allelopathy and less herbicides effect on weed management in field crops and soil biota: a review

Weeds cause serious yield reductions and lower the productivity of field crops worldwide. Chemical control is an efficient method to control weeds, and herbicides account for two third of total pesticide usage in the world. Nevertheless, continuous and indiscriminate use of synthetic herbicides in heavy doses is creating hazardous effects related to environment and an alarming number of herbicide-resistant weeds. Hence, it is imperative to find out some natural practice or method to control the weeds. Allelopathy has been found to offer ecofriendly approaches which can be used for controlling weeds effectively with least environmental concerns. Application of allelopathic crop extracts and residues is among the promising practical strategies for this purpose. However, in most cases, allelopathic extracts or crop residues provide limited weed suppression, and most often suppression in weed growth are not comparable to those achieved with labeled herbicide dose. Therefore, other methods that help increase the efficacy of allelopathic extracts or residues may be critical to enhance weed suppression while reducing our reliance on herbicides. Substantial scope exists to reduce the herbicide rate when lower rates of herbicides are applied in combination with aqueous extracts or residues of different allelopathic crops without any yield penalty. Moreover, the incorporation of crop residues also improves soil health with many implications on soil biota. The present article reviews the work concerning the combined effect of allelopathic water extracts and residues with lower rates of different herbicides on weed management and beneficial soil microorganisms in different cropping systems. Although this approach cannot discard use of synthetic herbicides completely but their use can be reduced up to a certain extent by utilizing allelopathy as an alternative weed management strategy for crop production as well as environmental benefits. The other advantages of this approach on soil properties are discussed. Some future lines of work are also suggested in this regard.