Changes in the soil due to the use of sheep in cover crop management in organic olive groves

This work studied the effects of cover crop management by livestock on soil properties, comparing it with other managements and uses of soil. For this, two olive-orchards were selected, one an ecological olive-orchard, surrounded by patches of natural vegetation and another under conventional management, both located in Pegalajar (Jaen, Spain). The study area was divided into 7 plots with four management types and three uses: two of the plots were not cultivated, one was lucerne (ESP) and the other one holm oak (ENC); one plot was under conventional management, with bare soil due to the application of herbicides (BL); one plot was managed by mechanical clearing (CON); three plots had a cover crop that was managed in the following ways: two plots with only sheep, for 2 years (G) and six years (GA) and the third plot with a combined management of livestock and mechanical clearing (Mix). The constituents and properties studied were: texture, bulk density, humidity, pH, exchangeable bases and cation exchange capacity (CIC), nitrogen (N), oxidizable organic carbon (CO), soluble organic carbon (COS), assimilable phosphorus (P), enzymatic activities beta-glucosidase and dehydrogenase. The organic carbon content was the constituent that most affected the other parameters. As expected, the soils under holm oak, followed by lucerne, showed the highest concentrations of total organic carbon and soluble organic carbon and nitrogen. However, the concentration of total carbon in soils with livestock management was equal to that of the lucerne. The sequences from highest to lowest concentration were ENC > GA, ESP, G > BL for total carbon, and ENC, ESP > CON, G, GA, MIX > BL for soluble carbon and nitrogen. In general bulk density and pH were lower in the uses and managements with higher CO content. On the contrary, the parameters of humidity, bases and cation exchange capacity were higher when the CO was also higher, although not always with significant differences. The beta-Glucosidase activity was lower in holm oak, probably because the organic matter has a lower cellulose content. Finally, the dehydrogenase activity was significantly higher in holm oak and lucerne, which have continuous contributions of organic matter that favour a continual microbial activity, contrary to the rest of treatments that are more time-specific.