Long-Term Impact of Two Native Shrub Cropping Systems on Yield, Carbon Sequestration, and Soil Nutrient Dynamics in Degraded Agroecosystems of Senegal.

Throughout the Sahel, two native shrubs, Guiera senegalensis and Piliostigma reticulatum, coexist at relatively low densities (0-300 shrubs ha^-1) with crops. A few studies have shown that these shrubs positively impact crop yields, but long-term data of these shrub intercrop systems’ effect on yields, soil nutrients, and carbon sequestration are lacking. Therefore, a 10-year study of an optimized (1500 shrubs ha^-1) shrub-intercropping study was initiated in 2004 in Senegal, West Africa with the objective to determine impacts of shrubs on soil quality, crop productivity, and drought stress resistance. The experiment was a split-plot factorial design with main plot shrub (with and without) and subplot of fertilizer rate (0, 0.5, 1, and 1.5 times the recommended N-P-K rate) at 2 sites in Senegal that had a peanut-pearl millet crop rotation. Yield, biomass, total organic carbon (TOC), soil N and P dynamics data from 2011-2014 were compared with data from 2004-2007. At the northern site with G. senegalensis, yields were consistently increased over the non-shrub plots at all fertilizer levels over the 10-year period. Whereas, at the southern site yield response to shrub presence was inclusive from 2004 to 2007 but in the 2011-2014 period yields, especially with millet, were significantly improved by P. reticulatum. Yields normalized for yearly rainfall (kg grain ha^-1 mm^-1 precipitation), showed that the presence of shrubs with or without fertilizer maintained yields even in very dry years compared to non-shrub plots where this yield ratio tracked rainfall. In addition, there was significantly more TOC (both sites) and N (northern site) in shrub+no fertilizer than no shrub+no fertilizer plots. The advantage of shrub-intercropping is that it is local resource that subsistence farmers can adopt, and our data show that an optimized system regenerates degraded soils, increases crop productivity, and would be an ecological approach to buffer climate change.