Olive Grove Fertilization in Spain

Fertilization is widely used in order to increase or maintain the quantity and quality of crop yield and to correct nutritional deficiencies. Spanish olive orchards are not an exception, where fertilization is usually implemented both under rainfed and irrigated conditions. However, the amount of fertilizer, composition, and application schedules are not usually subjected to technical criteria. This fact can lead to excessive application of some elements, or, in other cases, do not meet crop requirements. Works carried out in the SE of Andalusia revealed the great variability in the fertilizer contributions that are applied in olive groves with similar characteristics. In recent decades, fertilization advances have led to an improvement of the application efficiency, thus increasing the productivity of Spanish olive orchards. That improvement has contributed to increase sustainability of farming practices and to reduce the negative environmental impact derived from the abusive use of fertilizers. A rational fertilization must consider key elements such as the potential yield on the plantation, water availability, soil fertility, and nutritional status of the olive trees. Thus, fertilization is highly conditioned by rainfall and irrigation, allowing the dissolution of fertilizers applied to the soil and achieving satisfactory efficiency in their use. In Spanish rainfed olive groves (approx. 65% of the total olive groves surface) planted on limestone and/or clay soils, conventional soil fertilization usually is not very efficient at short term, although valuable results can be obtained in olive groves with middle-high productivity in the long term. On the other hand, we can identify a greater vegetative development and productive capacity in irrigated olive groves. In addition, the amount of the soil volume available for the olive tree, with high root activity and density, is significantly reduced, being mainly located in the wet bulbs, especially in dry years. Then, fertilization must be adjusted to these characteristics. Fertigation becomes an essential practice in order to maintain high production in the olive grove and to reduce the alternate bearing. However, the doses of the main macro-elements (N, P, K) must be adjusted according to the nutritional requirements of the crop to achieve a maximum efficiency. Excessive doses of some elements do not improve the production and can reduce the quality of the olive oil by reducing total polyphenols content and oxidative stability. The application of manure is not widespread in Spanish olive groves, due to the large surface area of these groves, which exceeds 2.5 million hectares, making the availability of manure scarce. Manure is used mainly in organic orchards. Proper management of composted oil mill pomace is an interesting alternative for the coming years, solving the growing problem of olive grove by-products and allowing to obtain a product with a high capacity to improve the physical-chemical properties of the soil. Nowadays, digital agriculture is imposing new practices in olive grove fertilization, such as nutrients control through direct measurements of sensors installed in irrigation heads or the use of drones equipped with multispectral cameras to identify tree deficiencies. These improvements are contributing to the agricultural development, increasing the fertilization efficiency and thus improving the profitability and environmental sustainability of the Spanish olive orchards.