Abstract
The effects of plant density on yield and yield components in upland rice cultivation were examined by conducting a series of field experiments in Central Uganda, using three African and one Japanese improved upland rice varieties. The estimation of plant-density response functions with respect to yield components and yield revealed that an increase in plant density significantly decreased the number of panicles per hill, number of spikelets per panicle, and 1000-grain weight, and significantly increased the number of panicles per square meter. The percentage of filled grain was not affected by plant density. Compared to the Japanese variety, the three African varieties were characterized by more numbers of panicles/hill, less numbers of spikelets/panicle, higher grain-filling ratio and lighter 1000-grain weight, but differences in the degrees of response to plant density were less distinct between them. Rice yield increased in the range of plant density tested, though the marginal increase in yield due to an increase in plant density by 1 hill/m2 diminished from 100 kg/ha at the plant density of 11 hills/m2 to 30 kg/ha at 33 hills/m2. No significant differences were found among the four varieties for the level of yield as well as for its degree of positive response to plant density. The yield components that determined the increase in yield were the number of panicles per square meter and the number of spikelets per panicle, or combined together, the number of spikelets per square meter, which was estimated to reach the maximum at the plant density of 35 hills/m2. When the differences among the treatments in the costs of seeds and weed-control were considered, the optimum plant density was found to be 22 hills/m2 (plant-spacing of 30 cm × 15 cm), lower than the plant density that gives the maximum yield. Key words: Economic optimum, maximum yield, NERICA, plant-density response function, yield components.
Highlights
Rice is a crop of importance in sub-Saharan Africa (SSA), the demand for which has been increasing most rapidly among major staple crops in the region (Seck et al, 2013)
The advent at the turn of the century of NERICA (New Rice for Africa), a series of upland rice varieties that are the interspecific progenies of Oryza glaberrima and O. sativa developed by the Africa Rice Center (AfricaRice, WARDA) (Jones et al, 1997), coupled with national as well as international efforts toward the development of rice production in SSA (AGRA/JICA, 2008), has helped to develop adapted upland varieties and promote upland rice cultivation in SSA
The means by season, varieties, and plant density treatment and by yield component indicated that an increase in plant density decreased panicles/hill and spikelets/panicle and increased panicles/m2 and yield, large variations across replications made the mean differences among the plant density treatments not significant for many cases (Table 1)
Summary
Rice is a crop of importance in sub-Saharan Africa (SSA), the demand for which has been increasing most rapidly among major staple crops in the region (Seck et al, 2013). There are, technical challenges to be addressed for the wider diffusion of upland rice cultivation in SSA, many of which stem from the fact that rice is relatively new, exotic, and unfamiliar crop for upland farmers in many parts of the region, in East Africa, except for Madagascar (Badawi et al, 2010). In SSA, Oyedokun (1977), Oyedokun and Sobulo (1977), Yamaguchi (1982), Akobundu and Ahissou (1985), Oikeh et al (2009), and Oghalo (2011) studied the effects of plant density in upland rice cultivation in West Africa, but no substantial efforts have been made to study on the effects of plant density and/or plant population in East Africa, except for NaCRRI (2010) that gives recommendations for upland rice plant spacing without published data
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