Soil Quality and Agricultural Sustainability of Dryland Tropical Farming Systems

Abstract A study was carried out to investigate soil quality of dryland farming systems of Mbeere District, Eastern Kenya and its implications on agricultural sustainability. Soil sampling was done in years 2002 and 2004 from 30 study farms and same sampling sites and from paired adjacent land-use systems (bush fallow and cultivated fields). Physical, chemical and biological laboratory analyses were carried out. Factor analysis showed that the main soil quality indicators for evaluating sustainability of the dryland farming systems of the district were texture; organic matter, exchangeable bases (Ca, Mg, K, and Na); extractable nutrients (P and Zn); and acidity (pH). Cultivated soils were characterised by low pH, nutrient deficiencies (N, P, Cu, and Zn) and low organic matter and a decline in organic C, total N, exchangeable K and extractable P across time. They were also lower in exchangeable bases and microbial biomass C than adjacent bush fallow soils. We conclude that the soils are degraded and farmin...