Rice Yields and Nitrogen Cycling Enhanced Using Novel Dual-purpose Cowpea-NERICA Ecotechnology in Degraded-savanna Upland Ecosystems.

Soil degradation and nutrients depletion are the most serious threats to crop production in Africa. Innovative strategies are needed to limit the rate of soil fertility loss and enhance productivity in fragile upland ecosystems. This study evaluated a novel ecotechnology involving an annual sequencing of dual-purpose early-maturing cowpeas with biomass incorporation before seeding extra-early maturing New Rice for Africa (NERICA^®) to enhance N cycling and rice productivity. In 2006 and 2007, four dual-purpose early-maturing cowpea cultivars (IT90-277-2, IT97-568-11, IT97K-1069-6, IT93-452-1), and popular local cultivar (Katchè) were seeded early in the wet season using five farmers’ fields at Ouake, northern Guinea savanna of Benin (9°46'N, 1°35'E; rainfall, 1108 mm [monomodal]). After pod harvest, cowpea crop residues were worked onto the soil using minimum tillage with hand hoe. Extra-early, resilient NERICA8 rice was seeded with 20 kg N ha^-1 or without nitrogen in each previous legume plot. Adjacent fallow plot was used to evaluate NERICA8 response to N at 0, 20, 40 and 60 kg/ha. Mineral N was monitored under NERICA rice. Nitrate-N was significantly higher by 60% in the topsoil (0–15 cm) of previous cv. IT97-568-11 plots than in the topsoil of previous fallow plots. Release of mineral N was sustained into the season in previous improved cowpea plots than in previous fallow plots. Also, previous plots of cowpea cv. IT97-568-11 supplied with limited N fertilizer (20 kg N ha^-1) gave 2.4 times greater paddy yield than paddy obtained from previous fallow plots without N (farmer-control). The N replacement value for using cv. IT97-568-11 before NERICA8 rice was estimated at 26 kg ha^-1, suggesting a saving in N fertilizer of 26 kg ha^-1. Results indicate that this technology could be used by smallholder farmers to enhance yields, improve soil fertility and stabilize fragile upland rice ecosystems.