摘要
The processes of nutrient depletion and soil degradation within smallholder farms of central Kenya are spatially heterogeneous, determined by both biophysical and socio-economic factors. A monitoring study involving nutrient stocks, flows and balances was conducted in central Kenya to explore between and within-farm variability in soil fertility management and identify spatial niches for targeting soil fertility management strategies. Focus group discussions were conducted and farms grouped into 3 farm types （rich, medium and poor）. Nine case-study farms - three from each of the farm types - were randomly selected from the 50 farms studied, for detailed resource flow mapping. The farms were visited to record movement of nutrients inputs using a monitoring protocol covering soil, crops, livestock, and socio-economic aspects of the farm. Soil in different plots were sampled at a depth of 0-20 cm and analyzed for texture, pH, C, N, available P, exchangeable K＋, Mg2＋ and Ca2＋. Results revealed that wealthy farmers added an average of 51.3 kg/ha N, 37 kg/ha P, and 244 kg/ha K, compared to 25.9 kg/ha N, 14.5 kg/ha P and 50.7 kg/ha K for the poor farmers. In all farm types, home fields received more nutrient inputs compared to the outfields. Consequently, maize grain yields, partial nutrient balances and soil nutrient stocks were significantly higher in wealthy farms and home fields compared to poor farms and outfields, respectively. These results imply that different soil management strategies are required to achieve similar yields on the different field and farm types and avert soil degradation.
