Effect of Olive Tree - Barley/Common Vetch Agroforestry System on Soil Organic Matter Under Low-Input Conditions in a Tunisian Semi-Arid Climate

The use of cover crops within olive groves, be they legume, non-legume or a mixture, has become more widespread in recent years as a practice of environmental sustainability to improve soil organic matter. Using both SC: a sole-crop and AC: an alley-cropping, Hordeum vulgare L. and Vicia sativa L. were studied with olive trees 2016 to 2019. The aim was to determine the effects of both of these systems on: TB: total biomass, POXC: Permanganate oxidizable Carbon and SOC: Soil Organic Carbon, TN: Total Nitrogen, C:N ratio; and P: available Phosphorus. These parameters were measured on 192 soil samples collected at 0-20 and 20-40 cm soil depths before planting and after crop harvesting. The results showed that within the relatively short time of three seasons, cover crops increased SOC slightly overall. Compared to the SC, AC limited crop and weed growth and produced significantly less TB, especially in 2017-18, a particularly dry season. This can be explained by the initial state of the soil which was significantly affected by the cropping system. AC enhanced SOC and stabilized the POXC during all three cropping seasons for all treatments. Mixed crop (barley and vetch) significantly increased TN in the AC over the three cropping seasons and decreased the C:N ratio. However, with barley and vetch in pure stand, the mean TN was similar to that of fallow. Also, this type of agroforestry increased the mean available phosphorus with barley, vetch and a mixture of the two compared to fallow.