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Soil is the physical support of the tree, and where it fulfills all its water needs and a large part of mineral nutrients.
Soil management needs to be more efficient in dry farming than in irrigated systems because if watering is impossible, the tree has to fulfill absolutely all its water needs from rainfall, so every drop must be used.
In a non-irrigated olive grove, it is necessary to maximize infiltration. Depending on the farm, deep tilling, vegetative covering, etc. can be used. High infiltration is synonymous with low runoff and, hence, little erosion--a very serious problem in hilly groves with little stone content.
Once the water has penetrated the soil, the aim is to get the highest percentage of the water back out into the atmosphere through the leaves of the olive trees, not through the leaves of the weeds or the natural porousness of the soil.
Again, depending on the farm, tilling is combined with the use of herbicides, physical removal or grazing.
Since plants need mineral salts, the presence of organic matter in the soil is extremely important. It improves the desireable characteristics of the soil in terms of plant life and, above all, it helps mineral nutrition very much in soils that have an excess of a given parameter such as active lime, clay, etc.
When organic substances in the soil decompose they give off hormone precursors of plants that activate plant metabolism.
Another extremely important positive effect of organic matter in soil is that it constitutes substance for beneficial microorganisms, which act as antagonists to other harmful microorganisms in the roots. In soil with little organic matter, there are few beneficial microorganisms, so root diseases like Verticillium can proliferate.
In the Mediterranean climate and its soils, the majority of which are calcareous, organic matter is rapidly decomposed, so the soil in olive groves naturally tends to be very poor in organic matter. Maintaining good levels of organic matter in the soil should be a constant part of soil management.
There are different ways for managing the soil which can be used in combination, and throughout the year. With the overall objectives of maximizing inflitration and minimizing runoff and evaporation, each parcel will be best served by one or another technique.
