The Hidden Costs of Soil Mining to Agricultural Sustainability in Developing Countries: A Case Study of Machakos District, Eastern Kenya

Soil nutrient budget studies are increasingly becoming important in determining the magnitude of nutrient mining in sub-Saharan Africa and its impacts on food production. A study of farms practicing low external input agriculture (LEIA) and conventional farming practices was made with regards to soil nutrient management in the semi-arid areas of Eastern Kenya over a two-year period using nutrient monitoring (NUTMON) methodology. Multidisciplinary, multiinstitutional and multi-scale approaches were adopted and quantitative and qualitative data on nutrient flows and stocks were collected through monthly farm interviews. Secondary data on farm inputs and outputs as well as data on soil nutrient stocks (soil sampling and analysis) were also collected. Soil nitrogen, phosphorus and potassium were being mined to comparable magnitudes in the two farming systems studied and 60% and 80% of farm income was based on nutrient mining in LEIA and conventional farms respectively. Although the use of farmyard manure was found to be the most cost-effective approach to replacing the mined nutrients within farmers' socioeconomic circumstances, it can only be effective within Integrated Nutrient Management framework that embodies the use of other soil fertility management technologies implemented within a conducive policy framework and broader livelihood strategies.