Amadou Touré

Responses of upland NERICA® rice varieties to nitrogen and plant density

Improved varieties, nitrogen fertilizer, and plant spacing have been identified for increasing upland rice productivity. However, these factors have not been adequately investigated on interspecific rice, New Rice for Africa (NERICA®). Different levels of nitrogen (0, 30, 60 and 120 kg ha−1) and plant spacing (dibbling: 30 × 30 cm, 20 × 20 cm, and drilling: 25 × 5 cm) on the growth and yield of three interspecific rice varieties and a check variety were evaluated on Terre de barre soils. Rainfall in both years was unevenly distribution which caused drought in both years. Across both years, rice yield was significantly depressed with 60N and 120N by 53–81%, compared with other N levels. NERICA4 with 30N gave the highest panicles density and harvest index, and the best yield (1.2 Mg ha−1). Wide spacing of 20 × 20 cm or 30 × 30 cm with four plants stand−1 was optimum for the NERICA. Drilling rice at 25 × 5 cm with one plant stand−1 depressed yield. Results showed that in smallholder upland ecosystems prone to unpredictable drought, wide spacing and low N can be recommended for production of NERICA.

Cultivar and Weeding Effects on Weeds and Rice Yields in a Degraded Upland Environment of the Coastal Savanna

Abstract Weeds are a major constraint to rice production in labor-limited, upland rice-based systems in West Africa. The effects of weeding regimes and rice cultivars on weed growth and rice yield were investigated at two upland locations (Abomey-Calavi and Niaouli) in the degraded coastal savanna zone of Benin in 2005 and 2006 with below-average rainfall. Four weeding regimes (hoe weeding at 21 d after sowing [DAS], delayed hoe weeding at 31 DAS, hoe weeding at 21 and 42 DAS, and a no weeding control) were the main plot treatments. Cultivars comprising three interspecific upland rice cultivars (NERICA 1, NERICA 2, and NERICA 7) and the parents (Oryza sativa WAB56-104 and O. glaberrima CG14) were tested in subplots. The most dominant weed species identified were Jamaican crabgrass, Mariscus, and silver spinach. Rice yield was generally low because of drought stress; none of the experiments had a higher mean yield than 1,400 kg ha−1 across cultivars. Across cultivars, the best weeding regimes in terms of weed control and rice yields were single weeding at 31 DAS (W31) and double weeding at 21 and 42 DAS (W21+42). Under these weeding regimes, WAB56-104 out-yielded the three NERICA cultivars. CG14 showed the strongest weed suppressive ability (WSA) in Abomey-Calavi but did not have strong WSA in Niaouli because of lower biomass accumulation. WSA of WAB56-104 was similar to that of the three NERICA cultivars. Single weeding at 31 DAS, together with the use of cultivars with good adaptation to unfavorable rice growing conditions, would increase land and labor productivity of upland rice-based systems in West Africa. Nomenclature: Jamaican crabgrass, Digitaria horizontalis Willd.; Mariscus, Mariscus alternifolius Vahl.; silver spinach, Celosia trigyna L.; rice, Oryza glaberrima Steud ‘CG14’; rice, Oryza sativa Linn. ‘WAB56-104’; rice, O. sativa × O. glaberrima, NERICA 1 ‘WAB450-IBP-38-HB’; rice, O. sativa × O. glaberrima, NERICA 2 ‘WAB450-11-1-P-31-1’; rice, O. sativa × O. glaberrima, NERICA 7 ‘WAB450-IBP-20-HB’.

A Case of Cyperus spp. and Imperata cylindrica Occurrences on Acrisol of the Dahomey Gap in South Benin as Affected by Soil Characteristics: A Strategy for Soil and Weed Management

Because of the limiting efficacy of common weed control methods on Cyperus spp. and Imperata cylindrica their occurrences in tropical agroecologies and the effect of soil properties in suppressing these species were investigated in south Benin (Cotonou), a typical ecology of the Dahomey gap. Weeds and soil samples were collected twice early and later in the rainy season in 2009 at four topographic positions (summit, upper slope, middle slope, and foot slope). Sampling was done according to Braun-Blanquet abundance indices (3 and 5) and the absence (0) of Cyperus and Imperata in a quadrat, respectively. The relationship between their respective abundances and soil parameters (texture, C, N, P, K, Na, Ca, Mg, and Fe) was explored. Weed occurrence was less related to soil texture, and Imperata growth was more influenced by soil nutrients (K, Ca, and Fe) than Cyperus spp. Soil cation ratios of K : Mg and Ca : Mg were the main factors that could be changed by applying K and/or Mg fertilizers to reduce Cyperus and/or Imperata occurrence. Maintaining high Fe concentration in soil at hillside positions can also reduce Imperata abundance, especially in the Dahomey gap.