Combining Soil Rhizosphere Microbiology and Hydrology with African Culture and Agriculture: 15 Years Research Characterizing Native Shrub-Intercrop Systems in Senegal.

The Sahel is experiencing landscape and soil degradation that reduces food and economic security of rural, underprivileged communities that depend on agro-ecosystem services. 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 water and nutrients. Conversely, two native shrubs, Piliostigma reticulatum and Guiera senegalensis, coexist with row crops throughout the Sahel and until recently have largely been overlooked. Consequently, these two shrubs being indigenous and already found in farmers’ fields to varying degrees, hold potential to meet these challenges. Unfortunately, the current management of spring coppicing and residue burning prior to cropping, is not utilizing this organic matter effectively. Prior to our research very little was known about the ecology or agronomy of these shrub-intercrop systems. Therefore, the global objective was to determine the unrecognized ecological function of these shrubs in agroecosystems of Senegal that are representative the Sahel. To test these hypotheses, our team over the last 14 years, has conducted extensive field based investigations in the Peanut Basin of Senegal that included: ground surveys and remote sensing to determine the 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. Phase I, graduated 4 PhD students and 3 post docs and had the following major findings:

• shrubs are by far the largest source of organic matter on the landscape in cropped fields
• shrubs increase soil quality
• decomposition rates of shrub residues are rapid and 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 diversity and processes year around, and assists 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 actually stimulate yield by as much as 3000 %
• repeated application of these low quality residues (in absence of live shrubs) begins increasing yields after 2 years.

Phase II has 4 PhD students, an MS student, and 1 post doc working on rhizosphere microbiology (beneficial microorganisms, mycorrhizal fungi, intercrop rhizosphere architecture, N fixation, and diazotrophs) and crop-shrub water relations (rhizosphere hydrology, drainage, and drought stress).