Abstract
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 NO3-N and PO4-P concentrations. In all treatments runoff had higher concentrations of NO3-N (2.20-4.83 mg L-1) than of PO4-P (0.02-0.07 mg L-1), and the eroded soil had higher content of PO4-P (5.27-18.8 mg g-1) than of NO3-N (1.30-8.51 mg g-1). The control had significantly higher losses of both NO3-N (5.4, 4.4 and 19 kg ha-1) and PO4-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 NO3-N and PO4-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 NO3-N and PO4-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.
Highlights
A combination of nutrient depletion, mismanagement of fragile ecosystems, and harsh climatic conditions can lead to soil degradation in arid and semiarid regions, in the Sahel region, that threatens the sustainability of dryland agricultural systems [1,2,3,4,5,6,7,8]
This study evaluated the efficacy of selected strategies of soil-water management combined with organic amendments on N and P losses with eroded soil, and runoff and on crop yields in Cabo Verde drylands
Our results indicated that most of the NO3-N was lost in the runoff and most of the PO4-P was lost in the eroded soil, as reported by other studies [5, 22, 52]
Summary
A combination of nutrient depletion, mismanagement of fragile ecosystems, and harsh climatic conditions can lead to soil degradation in arid and semiarid regions, in the Sahel region, that threatens the sustainability of dryland agricultural systems [1,2,3,4,5,6,7,8]. Nutrient depletion, and other forms of land degradation reduce crop productivity per unit of water [9, 10] and affect water availability, quality, and storage. Erosion by water is the most common form of land degradation worldwide and usually increases with agricultural activity, with annual cropping systems where the soil surface is seasonally exposed to rain with high intensities [4, 12]. Thins the soil layer, reduces rooting depth, damages soil structure, and reduces infiltration, resulting in negative nutrient balances and lower crop yields in most farming systems in West Africa [4, 5, 12, 13, 14] and parts of Asia [15,16,17]
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