Effects of Land Management on Runoff, Erosion and Crop Production in a Semi-Arid Area of Kenya

Abstract

Field studies were initiated in 1990 to determine the sustainability of traditional and improved management practices. The management practices investigated were cropping density, surface cover (mulch and canopy) and two tillage options involving a conventional, (CT) and a minimum (MT) system. Daily rainfall, runoff, soil loss weekly soil water, mulch cover and seasonal crop yields were measured. Analysis of results of 19 cropping seasons showed that both runoff and soil loss decreased as cover increased. Mulch cover was more effective than the growing crops canopy. Average seasonal runoff declined from 74.4 mm (21.9% of rainfall) in the traditional maize system to 22.3 mm (6.5% of rainfall) in the mulched plots. The effect of low mulch rate was more dramatic in soil loss reduction than in runoff reduction. Crop yield increased with cover, from an average of 1 t ha⁻¹ in the traditional maize system to 2.75 t ha⁻¹ in the mulched plots. However, this increase was only realised with additional nutrients. CT was superior to MT in terms of runoff and soil erosion reduction. Mean seasonal loss for CT and MT were 30.7 mm and 77.1 mm, respectively, for runoff, and 1.84 t ha⁻¹ and 7.78 t ha⁻¹, respectively, for soil erosion. The most sustainable management system consisted of a conventional tillage system, double the traditional farmer maize crop density, retention of approximately 3 t ha⁻¹ of maize stubble as mulch and addition of 70 kg ha⁻¹ of nitrogen.