Soil quality indicators in response to long-term cover crop management in a Mediterranean organic olive system

Abstract

The study examined the effects of cover crop management on soil chemical and biological parameters and certain integrated indices, across 3 years in samples collected in spring and autumn, at three different soil depths (0–5, 5–10 and 10–20 cm) in an organic olive orchard in SE Spain. The organic management regimes were: an annual cover crop of vetch (Vicia sativa L.) (i) leaving the debris on the soil surface or (ii) mixing the debris into the soil, and (iii) mixing the annual weed cover into the soil. Adjacent plots under integrated production management were included for comparison. In general, the organic treatments showed higher values for organic carbon, nitrogen, microbial biomass and for the grouped enzymatic activities, but lower phosphorous than the integrated regime. For pH and electrical conductivity the results were more influenced by seasonal variability than by treatments. In general, the highest values resulted from the use of leguminous cover crops, leaving the crop debris on the soil surface and the differences being more notable in the uppermost layers of the soil. All treatments showed a gradient in the chemical and biological parameters in depth. These findings were supported by the results of the integrated indices, considered as overall indicators of soil quality. All the available information implied that, in general, the organic systems presented the best chemical and microbiological characteristics, especially with the input of leguminous cover crops leaving the debris on the soil surface. Nevertheless, attention should be paid to the availability of phosphorous in calcareous soils.