Soil and water conservation in semi-arid Kenya

Sub-Saharan Africa is beset by an increasing population putting stringent demands on a declining resource base. Soil and water conservation (S&WC) is often seen as the primary means to arrest the inevitable decline in soil quality and maintain the productivity of farming systems upon which the majority of the populace rely for their precarious living standards. Yet S&WC programmes have a patchy record: in humid areas they may be relatively successful, but in semi-arid areas there is neither evidence of widespread adoption of S&WC nor increased production. These marginal areas, economically and climatically present the most intractable challenge to natural resource managers. This study investigates the performance of S&WC in rainfed cropping in the drier parts of Kenya, paying particular emphasis to the yield benefits and economic viability of crop production systems for the small scale and most vulnerable of the rural land users. Results are based upon a series of experiments conducted over three crop growing seasons on three soils, testing 10 S&WC based crop production systems with a monocrop of 75-day (short-season) maize (Zea mays L.: var. Makueni composite). The S&WC measures range from physical techniques of contour tillage, tied ridging and terraces to a partly biological technique of trashlines. Hand tillage was taken as the control. In this marginal environment (agro-climatic zones IV and V), the typical situation of smallscale farmers adding no fertilizer was compared with currently recommended levels of application of fertilizer and manure