Effects of different olive-grove management systems on the organic carbon and nitrogen content of the soil in Jaén (Spain)

A judicious combination of agricultural soil management and conservation practices can help to increase carbon and nitrogen levels in the soil. This study examines the effect of five olive-grove soil-management systems (tillage, T; non-tillage with bare soil, NC; cover crops + herbicides, CH; cover crops + mower, CM; cover crops + mower + one pass of the disk harrow, CMD) on soil organic carbon and nitrogen content, evaluated over a 28-year trial in southern Spain (Jaén).The large quantity of biomass generated in all the treatments except NC, together with textural differences, modified the bulk density of the soil. With the CM and CH treatments, the concentration of soil organic carbon (SOC) was high at the surface and decreased with depth whilst T, NC and CMD resulted in more homogeneous concentrations at all the depths studied.The soil organic carbon pool correlated well with the clay pool in treatments applied to soils with more homogeneous textures and less biomass containing (CMD and NC). The highest SOC pool values appear on the surface (0–5 cm) with cover treatments (between 10.2 and 12.2 Mg ha−1). When the entire profile is taken into account (0–30 cm), CMD and T present the highest values (42.1 and 39 Mg ha−1). The lowest values are those of NC (22.8 Mg ha−1). The N pool behaves in a similar way. Olive-grove cover crop systems (CH, CM and CMD) must therefore be considered as an efficient agronomic practice for soil carbon fixation.