Socio-economic factors, soil fertility management and cropping practices in mixed farming systems of sub-Saharan Africa: a study in Kiambu, Central Highlands of Kenya

A study was carried out in Kiambu District, central highlands of Kenya to explore the effects of household socio-economic factors on farm nutrient balances and agro-economic performance and to determine nutrient depleting and conserving cropping practices in the crop-dairy (mixed) farming system. Data was collected from 30 smallholder farmers and processed using nutrient monitoring (NUTMON) tool. Family earnings (sum of net farm income and off-farm income) were low and off-farm income accounted for 61% of family earnings of the studied households. On-farm livestock density (TLU ha-1) was the main determinant of farm N, P and K nutrient stocks and balances. The mean farm (total) nutrient balances were -2.6 kg N ha-1 half year-1, 36.7 kg P ha-1 half year-1 and 16.9 kg K ha-1 half year-1. In the analysis, purchased livestock feeds (and fertilizers) were the major determinants of farm N, P and K nutrient balances. The major loss pathway for P and K was erosion, accounting for 35 and 66% of total P and K outflows respectively. For N, it was leaching. Farmers adopted preferential soil fertility management strategies for cropping practices resulting in nitrogen, phosphorus and potassium nutrient mining under Napier (monocrop) and coffee (intercrop) fields and nutrient conservation under maize (intercrop) fields.