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.

Soil organic matter (SOM) is known to play vital roles in the maintenance and improvement of many soil properties and processes. These roles, which largely influence soil functions, are a pool of specific contributions of different components of SOM. The soil functions, in turn, normally define the level of soil degradation, viewed as quantifiable temporal changes in a soil that impairs its quality. This paper aims at providing a generalized assessment of the current state of knowledge on the usefulness of SOM in monitoring soil degradation, based on its influence on the physical, chemical and biological properties and processes of soils. Emphasis is placed particularly on the effect of SOM on soil structure and availability of plant nutrients. Although these properties are discussed separately, the soil system is of dynamic and interactive nature, and changes in one property will likely affect other soil properties as well. Thus, functions of SOM almost always affect various soil properties and processes and engage in multiple reactions. In view of its role in soil aggregation and erosion control, in availability of plant nutrients and in ameliorating other forms of soil degradation than erosion, SOM has proven to be an important indicator of soil degradation. It has been suggested, however, that rather than the absolute amount, temporal change and potential amount of SOM be considered in its use as indicator of soil degradation, and that SOM may not be an all-purpose indicator. Whilst SOM remains a candidate without substitute as long as a one-parameter indicator of soil degradation is needed, narrowing down to the use of its labile and microbial components could be more appropriate, since early detection is important in the control and management of soil degradation.

No abstract

No abstract

No abstract

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.

No abstract

No abstract