Tomato

Nitrogen is the nutrient element to be treated more carefully. An excess of N can cause an excess of vegetative vigor, with consequent delay and scaling of ripening and greater susceptibility to fungal attacks. Depending on the period, nitrogen excess may also cause the formation of hollow fruits. Nitrogen fertilization must therefore be dosed with attention to both organic and mineral contributions, following the seasonal evolution that greatly influences the availability and absorption of nitrogen, without ever neglecting the balance with phosphorus and potassium which can contain the problems related to any nitrogen excess.The deficiency in nitrogen is manifested by a light green coloring of the leaves and a reduction in growth. The combination of an excess of nitrogen and a low intake of phosphorus and potassium can favor coloring defects.

Phosphorus is an element that intervenes in the growth of the roots, in bloom, in flower fertilization and fruit ripening.
It has an action on precocity: in fact, it has been found that the use of phosphorus determines a well-formed root system and improves earliness of ripening.
Phosphorus is essential for tomato growth. It does not require large quantities, but the assimilation of this element is not very efficient, especially in calcareous soils. Therefore, the availability of phosphorus must be guaranteed, with the use of fertilizers that contain it in a soluble and assimilable form from the plant.
The deficiencies are manifested by classic symptoms: stem and lower part of the leaves take on a purple color.
The deficiencies can be due to:
• Lack of phosphorus in the soil
• Parasitic attack on roots (nematodes)
• Ground temperature too low• Low brightness

Potassium has an action on the quality of the berries (taste and color) as well as on disease resistance.
The deficiencies occur with a light color of the foliage, to which follows the apparition of discolored spots that necrotize.
A lack of potassium favors the defects of discoloration on the fruits. An excess of potassium induces magnesium deficiencies.
The standard dose of potassium as K₂O is 300 kg/ha in poorly equipped soil, 200 kg/ha in medium equipped soil and 100 kg/ha in highly equipped soil, with the possibility of reduction or increase according to the different cultivation conditions.
Tomato prefers chlorine-free fertilizers such as potassium sulphate (K₂SO₄). In the case of use of potassium chloride (KCl) in the open field, it must be incorporated into the soil in autumn, in order to allow the leaching of chlorine.

Calcium is an important component for the structure of cell walls and stabilizes cell membranes. It also directly affects the salt balance in plant cells and activates potassium to regulate the opening and closing of stomata and to allow the movement of water in the plant. Bad assimilation of this element, generally due to poor irrigation management, causes apical necrosis or rot known as Blossom-end rot.
Calcium is required in fairly large quantities, equal to about 170 kg/ha of calcium for a yield of about 100 t / ha. Since calcium is necessary throughout the growth period and its transport in the fruit is slow, it is common practice to use the applications since the transplant and throughout the growing season, in order to optimize the quality and shelf life of the fruits.

20-25% of the total magnesium of the plant is localized in chloroplasts: this makes it a particularly important element for the production of chlorophyll and for photosynthesis.
The need for magnesium varies according to production and cultivation techniques.
Proper magnesium nutrition will partly avoid the problems of firmness and consistency of the fruit pulp.
Deficiencies are manifested by thickening and internerval chlorosis of the leaves.
The main causes of magnesium deficiencies depend on:
• Deficiency of the element in the soil.
• Lack of absorption caused by an excess of potassium.
• Radical asphyxiation.

Before transplanting:

The basic fertilization must include phosphorus and potassium. Nitrogen should be distributed in part before transplanting, using forms of nitrogen with prolonged action (ammonia or slow release), especially in light soils, and the remaining part on the plant cover.

After transplanting:

It is preferable that the transplant takes place in an already fertilized soil. If this is not possible, we can use a nutrient solution with 1-1.5 gr/liter of fertilizer. To prepare the solution we can choose a complete NPK fertilizer with a ratio close to 1-1-2 with the addition of calcium nitrate if necessary. If the transplant is done in a well enriched soil, fertigation will start starting from the third leaf.
With the fertilization on plant coverage the remaining part of nitrogen will be added, according to the vegetative development of the crop, the seasonal trend and the application technique, using quick-release fertilizer, such as calcium nitrate, ammonium nitrate and nitrate of potassium.
The distribution method is linked to the rate of absorption of the nutrient by the plant. Tomato is characterized by an almost parallel trend in the absorption of nitrogen and potassium with an absorption peak that normally falls between the fifth and ninth week of transplantation, in correspondence with the phase of rapid vegetative development and the beginning of flowering.
If you have a drip micro-irrigation system, (as is now common), fertigation can be applied. In this way it is possible to gradually distribute the fertilizers as the plants need them, automating the operation and simplifying the work.

Irrigation

Tomato is a plant with high water requirements, especially during the fruit enlargement phase.
Water requirements may vary according to the cultivation areas, the planting period, and the earliness of the crop. In general, close interventions are required, at least weekly, with watering volumes that are around 300-400 m³/ha /week. The first irrigation should be carried out when the residual water content in the first 40 cm of soil, measured by tensiometers, or estimated by means of a water balance, is approximately 50-60%.
It must be considered that among the most neglected aspects of irrigation management is undoubtedly the design of the irrigation and fertigation system. The adoption of unsuitable materials can make the effectiveness of the fertigation intervention almost null or cause significant damage to the crop or the environment.
The traditional perforated hose, for example, due to the known lack of homogeneity of water distribution, is not suitable for effective use for fertigation. The technique now offers new dripping hoses with flow rates and types of dripper labyrinth which, thanks also to a precise design and installation, allow a precise and regular distribution of water in the field, even in conditions of considerable length or terrain sloping.
The tomato plant can be considered on average tolerant to salinity, so waters with a modest / high saline content can be used.