Long-term effects of sustainable management practices on soil properties and crop yields in rainfed Mediterranean almond agroecosystems

The long-term effects of conservation agriculture on soil physical and chemical properties and their relationship with crop yields are still relatively poorly understood. In addition, the effects of those practices ranged widely depending on climatic and edaphic conditions and so they cannot be generalized for all agro-ecological regions and crop types. This study evaluates the effects of three conservation agriculture practices reduced tillage (RT), reduced tillage plus incorporation of green manure (RTG), and no-tillage (NT) on the soil quality on almond orchards under semiarid conditions and the soil factors explaining crop yield under these management practices. The soil physical indicators used were bulk density, resistance to penetration, total porosity, air capacity, relative field capacity, available water content, infiltration rate and field plant-available water content. The chemical parameters evaluated were soil organic carbon, total nitrogen, nitrate, and available phosphorus. Changes in the soil physical properties with the incorporation of green manure and with no-tillage, relative to RT were, mainly detected in the 5-15 cm soil layer, where improvements in soil water availability were observed. In addition, there was a positive effect of both green manure and no-tillage on the infiltration rate relative to RT. The shift from RT to RTG led to an improvement in total soil organic carbon and nitrogen, resulting in a positive effect on crop yield after six years of implementation. No-tillage led to a decline of about 70 % in crop yield with respect to the tillage treatments, despite the improvement in the soil available water content from the first year of its adoption. However, a strong decrease in the concentrations of available nitrogen was the factor mainly responsible for the crop yield reductions under NT.