RESPONSES OF NERICA RICE VARIETIES TO WEED INTERFERENCE IN THE GUINEA SAVANNAH UPLANDS

Abstract

The objective of this study was to determine the critical period of weed infestation in two newly developed NERICA rice varieties for upland rice production to support their dissemination to farmers. Two experiments were conducted between June to November, 2005 to evaluate the responses of two NERICA rice varieties 1 (site 1) and 2 (site 2) developed by the West African Rice Development Association (WARDA) to weed interference in the uplands in the northern Guinea savannah ecological zone. The randomized complete block design was used with treatments in four replications. Gravimetric soil moisture fluctuated (p<0.01) at both locations but remained in the range of 9.7-27.0 and 11-19.6% at site 1 and 2, respectively. Generally in both experiments, weed infestation up to 6 weeks after planting (WAP) or more reduced plant height at 12 and 15 WAP, Leaf Area Index (LAI), tiller count m-2, straw weight and grain yield. Keeping the varieties weed-free up to 6 WAP or more enhanced plant height at 12 and 15 WAP, LAI, tiller count m-2, straw weight and grain yield. In the present study, the critical period of weed infestation with the two varieties of NERICA in the upland ecology were similar and was between 3 and 6 WAP. This is an important guide for the NERICA rice dissemination programme in Ghana in particular and for medium maturity rice cropping in general for optimum timing of weed control to maximize yield components and grain yield. Season-long weed infestation resulted in 66 to 72% reduction in grain yield of the varieties, confirming the vulnerability of the varieties to weed infestation. The occurrence and composition of weeds at the two locations were similar with a mean of 66% broadleaves, 33% grasses and 11% sedges. The most dominant weeds were Brachiaria lata, Celosia laxa, Cleome rutidosperma, Commelina africana, C. benghalensis, Cyperus spp., Digitaria horizontalis, Mitracarpus villosus, Mollugo nudicaulis, Paspalum scrobiculatum and Scoparia dulcis.