Soil Biological and Physical Properties Under Conservation Agriculture in Kenya and Uganda.

Smallholder farming systems that dominate the tropical highlands of East Africa are faced with declining soil fertility, soil erosion and low crop productivity, threatening food security in the region. Hence, sustainable farming practices are required to restore soil fertility, control soil loss and enhance crop productivity. Conservation agriculture (CA) has been proposed as such an alternative with the potential of sequestering soil carbon and improving soil quality while sustaining higher crop productivity. This study assessed the impact of CA practices on total and labile soil carbon and nitrogen pools, aggregate stability, hydraulic properties and soil erosion control under four sites on an elevation gradient. Tillage systems included no-till (NT), minimum tillage (MT) compared with conventional tillage (CT), all combined with crop rotations and a cover crop or crop residue retention. Our results indicate that SOC and total nitrogen were consistently higher under MT across all sites except one steep, high-elevation site, though significant effects of tillage and cropping system interaction were only noted at one low-elevation site. Penetration resistance and bulk density tended to decrease with tillage and were in the order NT> MT> CT, whereas infiltration rate was not significantly influenced by tillage. The Revised Universal Soil Loss Equation (RUSLE2) model and GIS were used to predict the potential impact of CA practices on soil erosion. Soil loss was highest under CT without crop residue retention, averaging 206 and 78 Mg ha-1 yr-1 and lowest under NT+50% crop residue at 19.7 and 7.5 Mg ha-1 yr-1 in Kapchorwa and Trans Nzoia respectively. Comparatively, soil loss was in the order CT+0% residue> CT+30% residue> MT+30% residue> NT+30% residue> MT+50% residue> NT+50% residue. However, final soil loss was still higher than allowable T value in Kapchorwa, indicating a need for alternative management or change of land use. Overall, CA practices showed potential of enhancing sustainability under smallholder farming systems, but long-term studies are required to ascertain trends and adjust to local conditions.