The universal soil loss equation (USLE) and water erosion prediction project (WEPP) (inter-rill and rill) erodibility factors are important indicators for land degradation assessment all over the world, which were primarily developed for the United States of America (USA). However, information on suitability of USLE and WEPP for tropical environment is scarce. Therefore, studies were carried out to investigate the suitability of USLE and WEPP for selected tropical soils of Southwestern Nigeria. Four pedons classified based on USDA soil taxonomy as Plinthic Petraquept (Adio series), Kanhaplic Haplaustalf (Oyo series), Typic Plinthustalf (Temidire series) and Typic Haplaustalf (Owutu series) were used for the study. Soil erodibility factor was determined using USLE and WEPP models. Origin-Pro. 8.1 software was employed to compare USLE and WEPP models for conformity and suitability. The results showed perfect agreement (R2= 1.0;P< 0.001) between the two WEPP (inter-rill and rill) erodibility models in all the four soil types investigated. In addition, WEPP models (inter-rill and rill erodibility) significantly (R2= 0.82;P< 0.001) related to USLE (El-Swaify and Dangler, 1977) erodibility model. There was a poor relationship (R2= 0.46;P< 0.06) between USLE (Wischmeier and Mannering, 1968) and the WEPP erodibility factors. The WEPP erodibility models with a perfect relationship with soil properties of the four soil types are more suitable than USLE models for predicting soil erodibility of the identified soil types in tropical environments.
Cassava is the most important food crop in Africa occupying about 6 million hectares (ha). Several factors have limited the continuous and sustainable production of cassava in tropical Africa. Some of these factors include (but not necessarily limited to) soil and water, which are the two basic fundamental resources for cassava production. The demand on soil and water resources is increasing, especially for new and conflicting soil functions like enhancing crop production, improving water quality and mitigating climate change. Soil-plant-water relations relate to the physical properties of soil and plants that affect the movement, retention and use of water. This chapter reviewed the soil, water and plant relationship for cassava production in tropical Nigeria. The study observed that understanding the effects of soil quality and water characteristics on cassava production and its management as well as the relationship between soil, water and crop for sustainable optimum cassava production is highly imperative now than ever before, especially in developing countries of Africa (like Nigeria) that are characterised by high risks of soil degradation, rising populations and pressure on agricultural lands juxtaposed with predominant resource-poor and small landholders.
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