Nitrogen Dynamics and Enzyme Activities of Shrub-Millet Intercropping Systems in the Sahel.

Soils in the agricultural systems of the Sahel region are of inherently low quality and are suffering from rapid organic matter and nutrient loss. Furthermore, agriculture in this region is mainly rain fed and very susceptible to climatic changes and desertification. As a result, food security in the Sahel is a major concern. However, in the semiarid zone of Senegal, there is evidence that two local woody shrub species (Guiera senegalensis and Piliostigma reticulatum) are effective in promoting crop productivity when intercropped with millet and peanut. Both shrubs are capable of performing hydraulic lift, bringing water from the wet subsurface to the dry soil surface. This minimizes water stress in the surrounding soil, and helps support microbial communities. Yet little is known about the microbial communities associated with the shrub rhizospheres and the role they play in nutrient cycling. Therefore, the objectives of this research were to determine the shrub’s influence on enzymatic activity and nitrogen dynamics in the surrounding soil. Soil was sampled from shrub-millet fields throughout Senegal’s Peanut Basin during the 2012 and 2013 growing seasons. Enzyme activities related to nitrogen, carbon, and phosphorus cycling were measured. In addition, ¹⁵N incubations were performed to determine the shrub’s effect on nitrogen fixation. β-glucosidase, β-glucosaminidase, and acid phosphatase activities were significantly higher (p < 0.05) in soil samples collected within the influence of G. senegalensis. Furthermore, higher nitrogen fixation rates were found in soil collected from within the influence of G. senegalensis and P. reticulatum. These results indicate that the shrubs have a positive impact on nutrient cycling and decomposition in the surrounding soil, thus enhancing soil fertility and crop productivity. The results from this research provide further evidence that these intercropping systems can serve as an economically and environmentally sustainable means to increase crop yields in vulnerable Sahel ecosystems.