Safety of Oilseed Rape Straw Mulch of Different Lengths to Rice and Its Suppressive Effects on Weeds
Rice is widely grown after harvesting of oilseed rape (Brassica napus L.) in many countries. Experiments were carried out under greenhouse and field conditions to assess the impact of oilseed rape straw mulch on rice and paddy weeds. Oilseed rape mulch (900 g m−2) from straw 1-to-7 cm long was found to be safe for rice, when applied four days after sowing (DAS) in direct-seeded rice or four days after transplanting (DAT). In the meantime, the biomass of Echinochloa crus-galli (L.) P. Beauv. was reduced 65.74%, 80.18%, 81.15%, 70.99%, 55.65%, and 27.22%, respectively, when mulched with powder, and 1, 3, 5, 7, and 9-cm long oilseed rape straw, respectively, and the biomass reductions in Leptochloa chinensis (L.) Nees., Ludwigia prostrata Roxb., Ammannia auriculata Willd., and Cyperus difformis L. were all above 97% when mulched with 1 cm-length straw. The results of a field trial confirmed that oilseed rape straw mulch (900 g m−2) of 1 cm length was safe for rice. Moreover, weed suppression was as effective as the standard herbicide (oxadiargyl + butachlor 525 g ai ha−1) treatment. These findings demonstrate the potential to manage paddy rice weeds in an effective and environmentally sound manner by mulching with the straw of a preceding crop, oilseed rape.