Degradation of soil fertility following cycles of cotton-cereal cultivation in Mali, West Africa: A first approximation to the problem

Common agricultural practice in West Africa involves alternating crop cultivation for 10-12 years and thereafter leaving the field to rest (fallow) for 10-15 years. With increasing population pressure and growing demand for food on the one hand, and the lack of unexploited lands on the other, soils undergo fast degradation. In an attempt to predict soil degradation, 12 fields were sampled around Kita, Mali. Seven of these fields were under cultivation whereas the remaining fields were fallow or virgin soils. The soil pH, electrical conductivity, N-NO₃, N-NH₄, P, K, and the soil organic matter (SOM) were determined. Of all variables, only nitrogen and SOM showed significant linear relationship with cotton lint at the cultivated fields, with SOM being the only variable showing a clear threshold (of 18 t/ha) that distinguishes between fertile and infertile fields. Based on field observations a simple model of the family agricultural land use is presented, aiming to provide a link between agriculture practice and soil degradation. The model demonstrates that the current practices of cultivation and fertilization will result in a slow but inevitable decrease of SOM, with SOM reaching, in 25-35 years, a critical level, below which cotton growth will no longer be economical. We thus conclude that the current practice of cultivation is inefficient and a new cultivation practice, which accounts for the cardinal role of SOM should be adopted.