Soil loss in an olive grove in Central Spain under cover crops and tillage treatments, and farmer perceptions

PURPOSE: Soil erosion is a threat for the sustainability of the grove production all over the world, and olive groves are where the highest erosion is achieved. This study aimed to (1) evaluate soil loss from water erosion in microplots (1 m²) under natural rainfall events in an olive grove managed with tillage and three different cover crops; (2) determine the main climatic factors on soil loss and selective transportation; and (3) survey the willingness of local farmers to adopt cover crops. MATERIALS AND METHODS: Over four hydrological years (2010 to 2014), tillage and three cover crop treatments have been assessed in a sloping olive grove in the Mediterranean area, in a semiarid climate and gypsiferous soil. The treatments were tillage (once a year), two annual covers (barley and legumes) and a permanent cover (Brachypodium distachyon). Soil loss was collected after each rainfall event, dried and weighted. Rainfall data was recorded and soil cover (%) was determined. Organic carbon (% OC) and texture were measured for sediments of tillage treatment to study their selective transportation. Local farmers were polled regarding their knowledge of the biophysical factors that affect soil conservation, their management practices and their willingness to adopt sustainable land management practices as cover crops. RESULTS AND DISCUSSION: The tillage treatment exhibited the highest soil loss (6.8 t ha⁻¹ year⁻¹). Cover crops significantly reduced soil loss: 40 % for legumes, 60 % for barley and permanent cover led to an 80 % decrease (1.4 t ha⁻¹ year⁻¹). The soil loss depends mainly on the soil cover and kinetic energy of rainfall events. Vegetation cover higher than 40 % in autumn and spring was essential to limiting soil loss, even under heavy events. Mobilised sediments were enriched 2.4 times in OC and 1.6 in the clay fraction. In spite of the well-known benefits of cover crops in soil conservation, local farmers do not use them. A lack of environmental education and awareness has been detected. CONCLUSIONS: Tillage in olive groves produced unsustainable rates of soil loss, while permanent cover demonstrated high efficiency. Gypsiferous soils are vulnerable to water erosion processes if they are not protected by vegetation. Farmers should adopt tailored soil cover practices during spring and autumn, when the soil loss is higher. A few farmers use sustainable soil management techniques, and therefore cover crops in olive groves are rare in Central Spain because farmers are reluctant to change.