Fifteen Years of African Research and Education: Hydrology and Microbiology of Shrub-Intercropped Rhizosphere for Optimizing Dryland Crop Yields in the Sahel.

KEY WORDS: Piliostigma reticulatum, Guiera senegalensis, soil remediation, Sahel, crop productivity

The Sahel is experiencing landscape and soil degradation that reduces food and economic security of rural, underprivileged communities. The Parkland system of randomly distributed trees is an approach to address these challenges, but trees are slow growing and can compete with crops for light, water, and/or nutrients. Conversely, two native shrubs, Piliostigma reticulatum and Guiera senegalensis, coexist in farmers’ fields throughout the Sahel and until recently have largely been overlooked. Unfortunately, the current management of spring coppicing and burning prior to cropping is not utilizing this organic matter effectively. Our team has done extensive field based investigations in the Peanut Basin of Senegal that included: ground surveys and remote sensing on landscape levels of shrub C and biomass; hydrology and water relations between shrubs and crops; rhizosphere microbiology; residue decomposition; N and P cycling in relation to crops; and crop productivity.  We found optimized, non-thermal shrub-crop systems have great potential for improving crop productivity and our research argues that it would be an ecological buffer for climate change in the Sahel. The major findings in Senegal are that:

• shrubs are by far the largest source of organic matter on the landscape in cropped fields
• shrubs increase soil quality
• decomposition rates are rapid enough to allow non-thermal residue management
• shrub roots perform hydraulic lift by moving water from wet sub- to dry surface-soils that appears to drive microbial processes year around and assist crops through drought periods
• shrub roots recharge groundwater in the rainy season, reducing runoff and conserving water
• shrub rhizospheres promote microbial diversity and harbour beneficial microbes
• intercropped shrubs do not compete with crops and significantly increase crop yields, with or without fertilizer inputs, especially in the annual rainfall of <600 mm.
• repeated application of these low quality residues (in absence of live shrubs) begins increasing yields after 2 years.