Improving agricultural productivity using agroforestry systems: Performance of millet, cowpea, and ziziphus-based cropping systems in West Africa Sahel

Across the drylands of sub-Saharan Africa, resource-poor farmers typically apply little or no organic or inorganic fertilizers; they remove or graze crop residues, leaving the soils nutrient-depleted and vulnerable to degradation. High temperatures, soil erosion, and declining soil fertility call for farming systems that protect fragile soils as well as improve nutrient availability and water use efficiency (WUE) and soil fertility. In the present study, the agronomic performance of an agroforestry system with millet (Pennisetum glaucum), cowpea (Vigna unguiculata), and Ziziphus (Ziziphus mauritiana) was compared to that of a cropping system without Ziziphus at ICRISAT research station, Sadore, Niger, for four years. The experiment was a factorial 3 x 4 design with three cropping systems: mono-cropping of millet (MM), mono-cropping of cowpea (CC), and millet/cowpea intercropping (M/C), and with four fertilizer treatments (FT) in a split-split arrangement. The same experimental design was installed on 2 blocks: with Ziziphus trees (ZT) at 80 plants ha(-1) and without Ziziphus (WZ). After the four years of cropping, ZT and WZ decreased SOC by 15 and 21 % and K by 105 and 110 %, respectively, compared with the original soil. Soil N was decreased only in the system WZ. Millet grain yields varied from 0.10 to 1.14 t/ha and the highest yields were obtained with NPK fertilizer alone or associated with farmyard manure (FYM) while the lowest yields were obtained with the control without fertilizer and FYM. The ZT system increased millet yields and its WUE with FYM and the control without fertilizer. However, millet yields decreased in ZT system with NPK fertilizer alone or associated with FYM. The ZT system increased the global annual incomes from 2-3 times compared with the system WZ. We concluded that including Ziziphus trees at the density of 80 plants ha(-1) to the low input cropping systems of smallholder farmers improve agricultural productivity and farmers' incomes. The proposed agroforestry system is affordable and compatible with the low input farming systems, and it ensures sustainable management of soils, land resources, and ecosystem services. But future research could contribute by identifying the optimal combinations of the density of Ziziphus trees, cropping systems and the doses of fertilizer on crops to optimize the productivity of the propose agroforestry system.