Trends in olive nutrition

Current knowledge suggest that a nutrient should be supplied only when there is evidence that it is needed to assure normal growth and productivity and when an economic response to fertilizer application is expected. However, current fertilization practice in many olive orchards is the repetition of fertilization programs, even when, in most cases, the nutritional status of the orchard was unknown. This practice usually leads to excessive fertilizer application. Leaf-nutrient analysis provides an indication of tree nutritional status and represents an important tool for determining fertilization requirements. Although this technique is becoming popular, leaf analysis is underutilized in olive growing. Predicting the amount of fertilizers required when leaf analysis indicates the need for fertilization is not simple. An estimation of tree consumption could provide some information about this need. The amount of nutrient removal by yield and pruning might be of interest. Potassium is the most abundant element in the olive fruit, and calcium the most abundant in the pruning material. Nitrogen is the second most abundant element in both fruits and pruning material. The other nutrients are removed in very small amounts, and usually are provided by soil solution. In accordance with these data, surveys and experiments conducted in different growing areas, the main nutritional imbalances that can affect the majority of olive orchards are represented by potassium deficiencies, mainly in drylands, calcium deficiencies, expected in acidic soils, and nitrogen overfertilization, since it is commonly applied in fertilization programs. Other imbalances are usually localized, such as iron deficiencies in calcareous soils, and boron and zinc in some areas where these nutrients are unavailable. In some areas, it is also common to find boron excess. Phosphorus is usually applied in fertilization programs, although it is very rare to reach phosphorus deficiencies since it is easily reused by the trees and phosphorus removal is low. Taking into account that the reserves of phosphate rock are finite, more responsible use of P fertilizers is required to minimize this problem.