Nitrogen is a nutrient that the olive tree, like all plants, uses in quantity, becoming part of proteins, enzymes, nucleic acids, chlorophyll and some vitamins necessary for the performance of plant biological functions.
An good nitrogen availability favors an increase in vegetative development and the quantity of product; However, it must not be exceeded, because there could be a slowdown in plant development, a lengthening of the biological cycle, greater water consumption, a reduction in resistance to climatic and parasitic adversities.
The two forms of nitrogen
In the soil nitrogen is found in two forms, one organic and one inorganic or mineral. L'organic nitrogen it is the one most represented in the soil: we find it of a predominantly protein nature - as derived from the decomposition of animal and plant remains - and in humus. To be absorbed by the roots, organic nitrogen must undergo mineralization or degradation, which is carried out by decomposer bacteria and fungi, which split it into simpler products, until ammonia and, from this, salts. ammonium and then to nitrates. The speed of this process depends above all on the temperature and humidity present in the soil, the best times for this reduction of compounds are in spring and autumn. Vice versa, in summer, due to the lack of water in the soil, and in winter due to the reduced temperatures they are much slower or canceled.
The roots have the ability to absorb ammonium salts and nitrates. They accept the latter more easily, because their presence is greater in the circulating solution of the soil, within which they move well dissolved and reach the surface of the roots extremely easily. Ammonium salts, on the other hand, are retained by the clays and the organic substance itself, therefore they are found in limited quantities and for very short times.
Absorption in the plant
Consequently, nitrogen absorption by plants is almost exclusively in the nitric form, assimilated by the root when the concentration of nitrates in the circulating soil solution exceeds that inside the root itself. Or, if the concentration of nitrates inside the root cells is higher than outside, the presence of transporter proteins is required.
Once the nitrates have entered the plant I am subjected to the action of enzymes transformation into ammoniacal nitrogen, this can happen immediately in the roots or in the chloroplasts of the leaves. If the absorption is already as ammoniacal nitrogen there is no this enzymatic step.
Once the plant has organic nitrogen available, it transforms it into amino acids and starches and then moves on to the synthesis of proteins, nucleotides and other molecules essential for the growth and development of the plant.
Nitrogen has considerable mobility within the plant, but this self-regulates it and keeps it in balance so as to allow correct functioning of all the biochemical reactions that occur within the cells, including the synthesis of proteins and nucleic acids.
Le greater nitrogen needs in the olive tree occur from March to July, with the awakening of the buds, with the growth of the shoots, with the formation of the flowers, with the setting and initial development of the fruits until the hardening of the stone.
At the vegetative restart, nitrogen is supplied by the reserve nitrogenous substances, accumulated in the previous autumn, which are translocated both towards the buds that must open and towards the formation of new vegetation. Root absorption, in fact, is still limited by the low temperatures of the soil, furthermore, the synthesis of energy substances by the leaves has not yet resumed at full speed.
The need for nitrogen in olive groves
In an olive grove the need for nitrogen, in the situation of an average production of oil olives estimated at 4 – 6 t/ha, is 90 – 100 kg/ha.
The distributions must be carried out in a fractional way so that the leaching of the nitrate nitrogen, being very mobile in the soil, is always very modest. Leaching is the movement of nitrogen by percolation water, which drags it along the soil profile beyond the layer affected by the root system of the plants.
The nitrogen distribution can be divided as follows,
1) 40% at vegetative growth (40 kg);
2) 30% before flowering (30 kg), to encourage fruit setting and increase the number of flowers;
3) 30% after fruit setting (30 kg) to support the first phase of pulp growth and hardening of the stone.
I nitrogen fertilizers, as we have seen, I can be:
- Nitrics, with a rapid effect, are unable to bind to soil particles, therefore it is easily washed away in case of heavy rainfall, for example calcium nitrate, average content 15%;
- Nitric Ammonia, with intermediate release, in this category we find ammonium nitrate, average strength 21%;
- Ammoniacal, with a more prolonged release, one of the most used fertilizers in this category is ammonium sulphate, average strength 21%;
-Urea, slow release, is one of the most commonly used fertilizers in agriculture, agricultural urea has an average content of 598%.
To increase the efficiency of nitrogen use, it is a good idea for the distribution to be uniform, so as to avoid there being an excess in some areas and a lower supply in others. It is also important to maintain a free band from fertilization at the edges of the plots, in order to reduce losses in the drains. Please remember that, after the distribution of fertilizers, they must always be lightly buried, even if the olive grove is covered in grass.
AIPO Director
Interregional Association
Olive producers
