Comparison of Physicochemical Properties of Soils under Contrasting Land Use Systems in Southwestern Nigeria

Abstract

Soil physicochemical properties were determined for soils under cropland and forest at the headquarters of the International Institute of Tropical Agriculture in Ibadan, Southwestern Nigeria to examine the 30-year effects of different land use on the fertility of five soil series toposequences underlain by a Basement Complex. The cropland had been under cultivation for 30 years, during which mainly maize and yams had been cultivated in rotation with application of chemical fertilizer and intermittent fallow, while the forest had secondary vegetation that had been regenerated during a 30-year period under protection. The findings for cropland indicated an accumulation of available phosphorus and exchangeable potassium, soil compaction and slight depletion of topsoil organic carbon content; and the findings for forest indicated soil acidification and accumulation of exchangeable Ca at the surface soil horizon. These findings suggest the possibility of maintaining soil fertility with a long-term intensive and continuous crop farming system in kaolinitic Alfisol soil over the inland valley toposequences of tropical Africa. Discipline: Soils, fertilizer and plant nutrition Additional key words: continuous cultivation, forest restoration, maintain soil fertility, IITA Present address: 4 Faculty of Life and Environmental Science, Shimane University (Matsue, Shimane 690-8504, Japan) *Corresponding author: e-mail wakatuki@life.shimane-u.ac.jp Received 10 February 2014; accepted 6 April 2015. Introduction Soil degradation and fertility depletion are the fundamental reasons for the decline of per-capita food production, hunger and malnutrition in Sub-Saharan Africa (Sanchez et al. 1997). It is estimated that the soils in this region have suffered an annual loss of 22 kg N ha1, 2.5 kg P ha1, and 15 kg K ha1 as a result of low input farming systems for subsistence such as traditional slash-and-burn practices over the past 30 years (Smaling et al. 1997). This annual loss is equivalent to US $4 billion in fertilizer (Sanchez 2002). The longer cultivation period and shortened fallow duration under ever-increasing demographic pressure have been threatening the productivity and sustainability of the traditional farming systems. Viable alternatives to these systems are required in the transition from traditional shifting cultivation to semi-permanent systems through the use of fertilizers. Soil fertility management is key to the sustainability of prolonged, semi-permanent farming systems that enable cropping intensification. Sanchez et al. (1982, 1983) documented an improvement in pH, exchangeable Ca and available P of soil in a highly weathered red soil (Typic Paleudult) of the Amazon Basin during an 8-year period of consecutive cultivation after forest clearing as a result of the application of chemical fertilizer (annual rates: 80100 kg N ha1, 25 kg P ha1, 80-100 kg K ha1). In contrast, Juo and Lal (1977) and Juo et al. (1995a, 1995b, 1996) found a declining trend in the same soil properties and crop productivity in a kaolinitic Alfisol (Oxic Kandiustalf) of tropical Nigeria during a 10to 18-year period of consecutive cultivation despite continuous application of the