Journal
AGRICULTURE ECOSYSTEMS & ENVIRONMENT
Volume 94, Issue 1, Pages 1-15Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0167-8809(02)00019-1
Keywords
surface water redistribution; soil moisture patterns; topographic indices; soil water retention; planting densities; Prunus dulcis (Miller); southeast Spain
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The acreage of rainfed almond plantations (Prunus dulcis (Miller)) in Spain has rapidly increased during the last 30 years, reflecting a tendency towards specialisation in perennial, rainfed crops in many Mediterranean regions. Seminatural vegetation and diverse cropping systems have been converted into monocultures with low tree densities leaving the soil unprotected. This paper illustrates the contrast in water conservation strategies between traditional and modem almond plantations in the Murcia region (Spain), and highlights the impacts of intensification on soil degradation. The role of lateral and vertical redistribution of soil moisture in water conservation will be discussed based on the analysis of soil moisture retention characteristics, temporal variation in soil moisture content and soil moisture patterns. A traditional cereal/almond cropping system typical for mart areas with a subdued relief will be compared to a modem almond monoculture in a highly dissected landscape on slate bedrock. The low water holding capacity of the stony soil in the slate area caused rainfall to penetrate deep in the profile and thus soil moisture fluxes were mainly vertical. Semivariograms of topsoil moisture content after an isolated rain day (19 and 27 mm for the nearest raingauges) demonstrated the differences in lateral redistribution of soil moisture between the cropping systems. A spatial pattern in the mart soil with a range of 69 m was observed, whereas soil moisture in the slate area showed no spatial pattern except for higher values in the narrow valley bottom. The scarcity of rainfall producing lateral redistribution of soil moisture explained the lack of reliable moisture supply in the mart area. This led to very low overall plant densities at 16 trees ha(-1), restricted to wetter zones upstream of retention dams. The redistribution of soil moisture by vertical fluxes in the stony soils of the slate area explained the uniform, widely spaced trees at densities of 204 trees ha(-1). This study has highlighted the need for rainfall to penetrate deep into the soil to sustain almond monocultures in semiarid climates. However, this requires a loose, bare topsoil between the trees and thus large areas of bare soil are exposed on hillslopes resulting in high erosion risks. (C) 2002 Elsevier Science B.V. All rights reserved.
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