Weed shift and community diversity in conservation and conventional agriculture systems in pigeonpea- castor systems under rainfed semi-arid tropics

Conservation agriculture (CA) is an alternative sustainable production system to conventional tillage system for resource conservation in rainfed agriculture. Weeds are the major constraints for adoption of CA in rainfed regions. A seven years study was done at ICAR- Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad, India, to study the effects of different tillage practices and residue levels on weed shift, diversity and crop yields. It was observed that annual weed species were dominant in conventional tillage (CT) and reduced tillage (RT), whereas a shift towards perennials was observed in zero tillage (ZT). The CT recorded significantly lower weed density and weed biomass (12.89 m- 2 and 35.60 g m-2) over RT (17.33 m- 2 and 38.37 g m-2) and ZT (36.67 m- 2 and 69.58 g m-2) after seven years, respectively. A shift in weed species, higher weed density and weed biomass in dicots (Tridax procumbens L and Euphorbia hirta L. and a marginal decrease in monocots (Bulbostylis barbata, Digitaria sanguinalis L) was observed in ZT. The marginal decrease in monocots was due to higher precipitation immediately after herbicide application which reduced the control of weeds due to leaching. The anchored residues 10 and 30 cm recorded lower monocots and total weed count over No residue. The study suggests that integrated weed management (combination of herbicide and removal of chance weeds) and in RT are efficient strategies to minimise the weed infestation in CA and these methods not only reduce the over reliance on herbicides but also improve the productivity of pigeon pea (Cajanus cajan L.), castor (Ricinus communis) and the environmental performance of CA. ZT and RT recorded the highest Shannon index, Pielous evenness index and species richness over CT which indicates a higher weed species diversity in ZT as compared to CT. This study helps to improve the understanding of crop-weed communities and in the development of cost effective environmentally sound weed management strategies.