Effect of Integrated Water-Nutrient Management Strategies on Soil Erosion Mediated Nutrient Loss and Crop Productivity in Cabo Verde Drylands

Soil erosion, runoff and related nutrient losses are a big risk for soil fertility in Cabo Verde drylands. In 2012, field trials were conducted in two agro-ecological zones to evaluate the effects of selected techniques of soil-water management combined with organic amendments (T1: compost/manure + soil surfactant; T2: compost/animal or green manure + pigeon-pea hedges + soil surfactant; T3: compost/animal or green manure + mulch + pigeon-pea hedges) on nitrogen (N) and phosphorus (P) losses in eroded soil and runoff and on crop yields. Three treatments and one control (traditional practice) were tested in field plots at three sites with a local maize variety and two types of beans. Runoff and eroded soil were collected after each erosive rain, quantified, and analysed for NO(3)-N and PO(4)-P concentrations. In all treatments runoff had higher concentrations of NO(3)-N (2.20-4.83 mg L(-1)) than of PO(4)-P (0.02-0.07 mg L(-1)), and the eroded soil had higher content of PO(4)-P (5.27-18.8 mg g(-1)) than of NO(3)-N (1.30-8.51 mg g(-1)). The control had significantly higher losses of both NO(3)-N (5.4, 4.4 and 19 kg ha(-1)) and PO(4)-P (0.2, 0.1 and 0.4 kg ha(-1)) than the other treatments. T3 reduced soil loss, runoff and nutrient losses to nearly a 100% while T1 and T2 reduced those losses from 43 to 88%. The losses of NO(3)-N and PO(4)-P were highly correlated with the amounts of runoff and eroded soil. Nutrient losses from the applied amendments were low (5.7% maximum), but the losses in the control could indicate long-term nutrient depletion in the soil (19 and 0.4 kg ha(-1) of NO(3)-N and PO(4)-P, respectively). T1-T3 did not consistently increase crop yield or biomass in all three sites, but T1 increased both crop yield and biomass. We conclude that T3 (combining crop-residue mulch with organic amendment and runoff hedges) is the best treatment for steep slope areas but, the pigeon-pea hedges need to be managed for higher maize yield. T1 (combining organic amendment with soil surfactant) could be a better choice for flatter areas with deeper soils.