Abstract

Weeds represent one of the major biological constraints to upland rice production in low input agricultural systems. The effects of weeding regimes and rice cultivars on weed growth and rice yield were investigated over three seasons. Four weeding regimes [0 (no weeding control), 1, 2, and 3] and three popular rice varieties (NARIC 2, a local cultivar, and NERICA 4), were tested in 4x3 factorial experiment in a Randomised Complete block with three replicates. The most important weed species recorded were; Biden pilosa, Commelina benghalensis L., Euphorbia hirta L., Micrococca mercurialis  Benth., Galisonga parviflora Cav, Sida rhombifolia L., Triumfeta spp, Guizotia scabra, Celocia trigyna, Cyprus rotundus, Panicum Maximum Jacq, and Imperata cylindrica L. Across cultivars, the best weeding regimes for weed control and rice yields were single weeding and weeding twice. Differences among interaction effects between variety and weeding regime were not significant for most traits, except ripening ratio and grain yield in experiment one and experiment two. Across weeding regimes, NERICA 4 out yielded the other varieties in all the three experiments. However, a single well timed hand hoe weeding, together with the use of a cultivar with good adaptation to unfavourable rice growing conditions, such as NERICA 4, would increase land and labour productivity of upland rice-based systems in Uganda.

Key words: Genotype, rice, upland, weeding regimes, yield.