Delivery of Hydrologic and Microbial Services by Indigenous Shrub Rhizospheres to Agroecosystems of the Sahel.

Abstract

The Sahel is experiencing landscape and soil degradation that reduces food and economic security of rural, underprivileged communities that depend on 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 in farmers’ fields 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 burning prior to cropping, is not utilizing this organic matter effectively.  There has been very little research on how to ecologically or agronomically manage these shrubs. Therefore, the global objective was to determine the unrecognized ecological function of these shrubs in agroecosystems of Senegal that are representative the Sahel. 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. 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.
• shrub roots recharge groundwater in the rainy season, reducing runoff and conserving water
• shrub rhizospheres promote microbial diversity and may harbour beneficial microbes
• intercropped shrubs do not compete with crops and actually stimulate yield by >50%
• repeated application of these low quality residues (in absence of live shrubs) begins increasing yields after 2 years.