The paper provides an insight into the problem of land degradation in Sub-Saharan Africa, with emphasis on soil erosion and its effect on soil quality and productivity, and proposes a lowland-based rice-production technology for coping with the situation. Crop yields are, in addition to the degree of past and current erosion, determined by a number of interacting variables. This, coupled with the generally weak database on erosion-induced losses in crop yield in spite of the region’s high vulnerability to erosion, makes it difficult to attain a reliable inference on the cause-effect relationship between soil loss and productivity. Available data suggest, however, that the region is at risk of not meeting up with the challenges of agriculture in this 21st century. Based on the few studies reviewed, methodology appears to have an overwhelming influence on the erosion-productivity response, whereas issues bordering on physical environment and soil affect the shape of the response curve. We argue that thesawahecotechnology has the potential of countering the negative agronomic and environmental impacts of land degradation in Sub-Saharan Africa. This is a farmer-oriented, low-cost system of managing soil, water, and nutrient resources for enhancing lowland rice productivity and realizing Green Revolution in the region.

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Although the West African inland valleys are characteristically wet all-year-round, their hydrological conditions are known to be site-specific and may differ markedly between the rainy and the dry seasons. Information on their physical properties would be useful for proper water management under the sawah rice culture and for planning dry season cropping. Representative inland valleys at four locations (Gadza, Nasarafu, Shaba-Maliki and Ejeti) around Bida in the Guinea savanna zone of Nigeria were selected for the study. Apart from Ejeti where the soil is clay loam, the predominant texture is sandy loam. The total and classified water-stable aggregates (WSA) were lowest at Ejeti, followed by Nasarafu. On the average, over 82% of the WSA were below 1.0 mm. Variations among the locations progressively decreased from the largest to the smallest aggregate-size class. Aggregate stability, as evaluated by both sand-corrected WSA and the mean weight diameter (MWD), followed similar trend as the WSA. Values were generally low for soil organic matter (SOM) (0.8-2.2%), but moderate for bulk density (0.98-1.55 Mg m -3 ) and total porosity (40.6-62.6%).Overall, Ejeti maintained the most favourable values of these three parameters, followed by Shaba-Maliki, Nasarafu and Gadza in the order listed. Micropores constituted over 87% of the soils' pore system. Saturated hydraulic conductivities were, however, highly variable; indicating lowest rates at Ejeti. Clay fraction correlated positively with the unstable (\0.25 mm) aggregates and porosity parameters, but negatively with other structural indices. The SOM correlated negatively and positively with MWD and total porosity, respectively. Soil-water management implications of these results are discussed.

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Failures in agricultural development in parts of West Africa may have been caused by the inability of the farmers to develop the abundant inland valleys for cultivation of such crops like rice, using appropriate water management systems. An inland valley in southeastern Nigeria was used to evaluate the influence of sawah and non-sawah water management using inorganic and organic soil amendments on the soil chemical properties and rice grain yield. Soil chemical properties tested were soil organic carbon, total nitrogen, pH, exchangeable K + , Ca 2+ and Mg 2+ . Others were CEC, percent base saturation and exchangeable acidity while the grain yield of rice was also measured. The soils are loose, low in pH and poor in plant nutrient elements. In spite of that, the sawah-managed system was able to improve the pH of the soil by raising it slightly both in the first and second year of planting. Generally, essential plant nutrients such as exchangeable K + , Ca 2+ and Mg 2+ , including fertility index like the CEC, were improved within sawah management within the period. Also, rice grain yield increased significantly (5.62 and 6.25 tons/ha in the first year and 5.32 and 6.53 tons/ha in the second year for non-sawah and sawah, respectively) with sawah system such that about 11 and 23% yield increases were obtained in sawah over the non-sawah in the two years, respectively. Although organic carbon can be used to explain the variation in total grain yield in the first year, it was the CEC that explained the total grain yield in the second year. The study revealed the superiority of sawah over non-sawah in the production of lowland rice in an inland valley in southeastern Nigeria.

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Purpose Rice-mill wastes are generated in large amounts in Ishiagu, Ebonyi State, Nigeria. These wastes can potentially be utilized for rice production and in improving soil attributes. This study evaluated the effects of rice-mill wastes on soil chemical properties and rice yield in sawah rice management. Methods A sawah rice field in an inland valley of southeastern Nigeria was used in 2014 and 2015 cropping seasons for the study. Sawah refers to an Indo-Malaysian term for rice paddy. It involves the manipulation of some soil physical properties in form of ecological engineering works, by bunding, puddling and leveling of lowland rice field for water control and management. Two rice-mill wastes [rice husk ash (RHA) and rice husk dust (RHD) applied at 0, 2.5, 5, 7.5, 10 and 12.5 t ha −1 ] and the control were built into a split-plot in a randomized complete block design with three replications. Results Bio-waste application had significant (p < 0.05) improved effects on the soil organic carbon, available P, soil available Si and total N compared with the unamended (control) treatment. There was significant (p < 0.05) increase in rice grain yield from 5.05 to 5.80 t ha −1 (for RHA) and 6.17-6.96 t/ha (for RHD) compared with 2.35-2.8 t ha −1 (control treatment) in both cropping seasons. Conclusion RHD and RHA treatments had significantly higher rice grain yield compared with the control treatment. Overall, rice grain yield was higher under RHD treatment compared with RHA treatment. This result demonstrated that RHA and RHD are potential agricultural resource for rice production in the study area.

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