Changes in soil properties due to continuous cultivation in Nigerian semiarid Savannah

A study to determine changes in soil properties related to traditional techniques of cultivation in the Nigerian semiarid Savannah was undertaken. Six sites located in a former forest reserve where environmental conditions were similar and where cultivation had occurred for 0, 3, 7, 11, 15, and 25 years were sampled and analyzed for key physical and chemical properties. Increasing years of cultivation resulted in increasing coarseness of texture and decreasing water stable aggregates >0.5 and 1.0 mm at 0-10 cm soil depth. Organic matter, total nitrogen, available phosphorus, exchange cations and cation exchange capacity (CEC had declined by 40-65% at 25 years of cultivation, although about half of these losses occurred during the first 3 years of cultivation. Only small changes in the properties were detected at 20-30 cm soil depth. Bulk density, exchangeable acidity and soil pH varied little in both soil layers. The results point toward progressive soil degradation following initial sharp fertility decline when the cultivation period become extended and external nutrient inputs were low or lacking. (C) 2002 Elsevier Science B.V. All rights reserved.