Upland rice growth and yield response to weed management practices under rainfed conditions in Morogoro, Tanzania

Field experiments were conducted in two seasons at the farm of Sokoine University of Agriculture in Morogoro, Tanzania (6.85°S; 37.64°E and 568 m.a.s.l.) during the short rain (November 2014 to January 2015) and the long rain (March to June 2015). The experiment was a split plot in randomized complete block design (RCBD) with 4 replicates. Weed management practices (herbicides, hoe weeding (3x) and weedy) were the main plot treatments; four rice genotypes (NERICA-1, NERICA-4, NERICA-7 and Mwangaza) were the subplots. Significant differences (P<0.05) were recorded on weed counts. Dominant weed groups as determined by Summed Dominance Ratio (SDR) in both experiments were broadleaf species (50.8%), sedges (25.2%) and grasses (24.0%). Post-emergence (8.6%) and hoe weeding (12.3%) significantly reduced weed dry biomass as compared to pre-emergence (17.8%) and weedy (61.3%) treatments in both experiments, respectively. Significant differences (P<0.05) were recorded among the rice variables. Data showed that Mwangaza and NERICA-1 had the tallest and shortest plant height (129.8 and 39.1 cm), respectively in both experiments. The highest and lowest tiller (35.3 and 7.5 m2) count was recorded for both these genotypes, respectively. The lowest and highest LAI (2.5 and 4.5) were recorded on Mwangaza and NERICA-7 respectively; and NERICA-7 had the highest and lowest straw biomass (1603 and 305.1 g/m2) in both experiments. The highest rice grain yield were recorded for NERICA-1 on hoe weeded plots and plots applied with post-emergence herbicide (2187.5 and 1562.5; 4176.1 and 4630.6 kg/ha) as compared to plots applied pre-emergence herbicide and weedy plots (965.9 and 0.0; 3323.8 and 0.78 kg/ha) in 2014/2015 and 2015 experiments, respectively. The highest return on investment, 3 352 846 Tanzanian shillings (Tshs) was obtained on NERICA-1 in post-emergence herbicide plots, and this was also similar (P<0.05) to hoe weeded plots. Post-emergence herbicide was also effective in weed control and had significant effect on profit analysis. This treatment/practice should be used in combination with hoe weeding under integrated weed management for better weed control. Key words: Weeds, management, upland rice, yields, growth, profitability.