Nutrient Management Research Database

Frequent tillage has been widely used in rainfed orchards in SE Spain in order to impede weed establishment and to increase water reposition in the soil profile. However, this practice may lead to soil degradation by decreasing structural stability, organic carbon content and microbial activity. This work examines the effect of different cover crop managements and frequent tillage on soil physical, chemical and biological properties in almond orchards in SE Spain. Two cover crops (oat – Avena sativa L. and oat-vetch – Vicia sativa L.) with two fertilization managements (mineral and organic) and three harvesting regimes (grazing in mid May, hay in early June, and grain-straw in mid July) were compared to a frequently tilled orchard system (three or four tillages per year). Most parameters were sensitive to soil management. Wet aggregate stability, total organic carbon, total nitrogen, carbon:nitrogen ratio, phosphatase, and β-glucosidase activities increased with cover crops, whereas the soil–water content declined, especially for the grain-straw treatment. The kind of fertilizer affected the available P content, which was higher for mineral fertilizer, and influenced the β-glucosidase activity, which augmented for the organic fertilizer. Livestock dejections depressed phosphatase activity, and increased WSC and available P. This study suggests that cover crops in semiarid environments improve soil quality compared to frequently tilled management, by increasing the organic matter content, improving the chemical and physical fertility of the soil, and enhancing the soil biological activity. Only higher water extraction by the plants could affect the orchard development and/or productivity; however, early cover crop removal would minimize possible yield losses.

• This study compared two ground cover management approaches in an almond orchard: cover cropping or frequent tillage.
• The study took place in semi-arid Spain, a climate similar to that in California.
• The use of both an oat only and an oat-vetch cover crop mix were paired with the use of organic or mineral fertilizers.

• The presence of cover crops increased soil organic carbon, total N, aggregate stability, and plant available P as compared to the tilled plots.
• However, no differences were observed between the plots planted with only oats and those with oats and vetch.
• Fertilizer source (i.e. mineral vs. manure) influenced soil patterns of soil moisture and P levels