Soil Organic Matter Changes Under Conservation Agriculture in the Mt Elgon Highlands of Kenya and Uganda.

Degradation of soil resources underlies yield gaps and nutritional deficiencies in Sub Saharan Africa and is a principle barrier to sustainable intensification that must occur, but there are persistent barriers to adoption of soil-building farming practices. Results of a five-year study indicate that conservation agriculture systems can effectively improve yields and soil quality in this densely populated region. Systems evaluated included three cropping systems: the farmer practice of maize-bean intercropping, a cover crop relay in maize-bean intercropping, and strip-intercropping in which maize, beans, and a cover crop are grown in monocultural strips narrow enough for advantageous interactions; and three tillage approaches: conventional moldboard plow, minimum tillage, and no tillage. Using mucuna as the cover crop, both alternative systems had similar or greater grain yields than conventional maize-bean intercropping. Soil organic matter, measured in 0-2.5, 2.5-5, 5-10, and 10-30 cm depth increments, became more stratified under no-till and minimum-till across all the cropping systems, but total carbon storage increased under the alternative tillage methods. Structured focus-group discussions with participating farmers, their neighbors, ag technicians, and others familiar with the project revealed a preference for the strip-intercrop system combined with minimum tillage because minimum tillage included more options for weed control compared with no till and decreased labor/traction needs compared with conventional tillage. Reasons for preferring the strip intercrop system included higher yields in the monocrop rotations, particularly for maize following mucuna, easier management of single-crop strips with cultivation or herbicides, and the observation that cash and labor outlays for maize could be concentrated on one-third of the area, increasing yields and reducing labor. Knowledge of fundamental crop and soil fertility management concepts is a primary need. Proper fertilization of smaller plots could maintain overall maize yields while reducing labor and creating space for soil building cover or forage crops.