No‐till with Stylosanthes guianensis cover crop affects weed community and improves weed management in upland rainfed rice in Madagascar

Abstract

AbstractIn Madagascar, upland rainfed rice is traditionally grown on tilled soil without transplanting. Weed infestation by annual species is a serious issue in such a system. Stylosanthes guianensis, a legume cover crop, can be grown with rice as a living mulch but its effect on the weed community and rice yield was not yet well studied. Therefore, a field experiment was conducted in Mid‐West Madagascar from 2016 to 2018. A no‐till system with stylosanthes (NT) managed as a living mulch was compared to the conventional tilled (CT) system. Two fertilisation regimes were included: organic manure (F1) and organic manure combined with mineral fertiliser (F2). Weed floristic surveys were performed, and weed harmfulness evaluated by comparing weedy and weed‐free plots. The living mulch harmfulness was evaluated using weed‐stylosanthes‐free plots. Results showed that NT suppressed dominant grass weeds Digitaria spp. and Eleusine indica leading to a decrease in total weed biomass. Rice yield was significantly higher in NT than in CT; in weed‐free condition, it was 2.4 versus 2 t ha−1 in NT and CT, respectively, and 1.5 versus 0.6 t ha−1 in NT and CT, respectively, in weedy condition. The living mulch reduced rice yield by 14% but it remained significantly higher in NT than in CT. The addition of mineral fertiliser to the organic manure had a positive effect on rice yield but only in weed‐free conditions. This study showed that a no‐till system with a living mulch can help to control the most competitive weeds without undermining rice production.