Improving rainwater-use in Cabo Verde drylands by reducing runoff and erosion

Abstract

Dryland agriculture in Cabo Verde copes with steep slopes, inadequate practices, irregular intense rain, recurrent droughts, high runoff rates, severe soil erosion and declining fertility, leading to the inefficient use of rainwater. Maize and beans occupy N80% of the arable land in low-input, low-yielding subsistence farming. Three collaborative field trials were conducted in different agroecological zones to evaluate the effects of water-conservation techniques (mulching of crop residue, a soil surfactant and pigeon-pea hedges) combined with organic amendments (compost and animal or green manure) on runoff and soil loss. During the 2011 and 2012 rainy seasons, three treatments and one control (traditional practice) were applied to 44- and 24-m2 field plots. A local maize variety and two types of beans were planted. Runoff and suspended sediments were collected and quantified after each daily erosive rainfall. Runoff occurred for rainfalls ≥50 mm (slope b10%, loamy Kastanozem), ≥60 mm (slope ≤23%, silt–clay–loam Regosol) and ≥40 mm (slope ≤37%, sandy loam Cambisol). Runoff was significantly reduced only with the mulch treatment on the slope N10% and in the treatment of surfactant with organic amendment on the slope b10%. Soil loss reached 16.6, 5.1, 6.6 and 0.4 Mg ha−1 on the Regosol (≤23% slope) for the control, surfactant, pigeon-pea and mulch/pigeon-pea (with organic amendment) treatments, respectively; 3.2, 0.9, 1.3 and 0.1 Mg ha−1 on the Cambisol (≤37% slope) and b0. 2 Mg ha−1 for all treatments and control on the Kastanozem (b10% slope). Erosion was highly positively correlated with runoff. Mulch with pigeon-pea combined with an organic amendment significantly reduced runoff and erosion from agricultural fields on steep slopes, contributing to improved use of rainwater at the plot level. Sustainable land management techniques, such as mulching with pigeon-pea hedges and an organic amendment, should be advocated and promoted for the semiarid hillsides of Cabo Verde prone to erosion to increase rainwater-use and to prevent further soil degradation.