Strawberry - Fragaria

The effects of nitrogen fertilizers on the main vegetative-productive parameters of the strawberry are strongly influenced by the doses and the epochs of administration.
A deficiency in nitrogen leads to a reduced and yellowish foliage, in the most serious cases, the leaves can become reddish starting from the ends.
On the contrary, an excess of nitrogen causes an abundant dark green foliage, an elongation of the petioles, to such an extent that the flowers and fruits remain inside the foliage. It also induces greater sensitivity to Botrytis. Excess nitrogen is a factor of bad quality and firmness of the fruit.
Nitrogen is mainly absorbed in nitric form. The presence of the ammonia form can be more or less unfavorable according to some conditions: at acid pH values, is advisable to carry out an essentially nitric nutrition.
The higher the root temperature, the more toxic the ammonia form becomes, in particular with temperatures above 30° C, where exclusively ammonia nutrition can lead to death of the plant. On the contrary, with low temperatures, the simultaneous presence of ammonia and nitric forms is desirable. 

Phosphorus is mainly absorbed starting from the flowering phase and during the subsequent development of the fruits, although the quantities are much lower than the other elements.
In particularly sensitive strawberry cultivars, the lack of P can determine the phenomenon of fruit albinism. In the presence of deficiencies, the old leaves take on a dark green / bronzed color. In soils naturally well endowed with P, the strawberry requirement for this element is generally already satisfied by the natural fertility of the soil; in such situations, further inputs of phosphate fertilizers have no marked effects.
Absorption is reduced in calcareous soils because phosphorus is insolubilized.

Potassium is present in the cationic form (K +) which plays an important role in regulating the osmotic potential of cells, in the water relations of the strawberry and in the photosynthetic potential. Potassium allows the synthesis of sugars and it has been shown that an increasing supply of potassium improves the sugar content and acidity of the fruit. These are the main quality factors of strawberries (flavor) but it has no effect on fruit conservation.
In case of deficiencies, the size of the leaves is reduced, the stolons are weak, the fruits are not very tasty and pale in color.
During flowering, more pronounced symptoms may appear, such as a diffuse browning of the leaf teeth and between the ribs. An excess of it can block the absorption of magnesium.
Strawberry is sensitive to chlorine, potassium chloride must be excluded.

The Ca²⁺ ion participates in the constitution of the cell wall and the middle lamella that is formed in the cell division process. 
Calcium is transported only passively through the xylematic system, following the transpiratory flow. It is an important element for root development.
Deficiency for this element is highlighted in young organs in formation (bud apices, young leaves) where symptoms of chlorosis and necrosis appear.
Calcium intakes (for example through fertigation) are suggested in soils poorly equipped with this element or in soilless cultivation with irrigated water containing little calcium.
In general, to avoid deficiencies, it is necessary not to exceed in nitrogen fertilization, as excessive doses of N lead to greater vegetative growth and in the emission of new leaves which, by transpiring, recall the absorbed Ca making it less available for fruits; in such situations, the fruits have a less consistent pulp and a reduced shelf life.

As with all plants, magnesium is essential in the synthesis of chlorophyll but does not affect the flavor of the fruit. Except for cases of full-blown deficiencies, magnesium does not affect the rate of dry matter, acidity and the rate of sugar in the fruit. On the contrary, it improves the red coloring.
The deficiencies are manifested by a redness/browning between the ribs of the old leaves. Afterwards the leaves curl up. In severe cases, the red coloration of the fruit can be severely slowed down.
Magnesium is absorbed throughout the active vegetation period of the strawberry grove and in particular during fruiting. Absorption is curbed by both a high potassium rate and a high pH.

To draw up fertilization plans suitable for different types of cultivation, it is necessary to know the chemical-physical characteristics of the soil, the chemical analysis of the water and the irrigation system.
When it is still possible, a basic fertilization with a good manure is a good rule, but it seems to be a more useful practice for maintaining a good soil structure than for nutritional supplies. Organic fertilization must be integrated with mineral fertilization, in particular with fertigation during cultivation.
The period of cultivation and therefore of fertilization varies according to the variety, and according to the cultivation technique, on or off the ground.
The everbearing varieties (early with long day) are transplanted in July-August, and an initial harvest is made in late summer / autumn, then after the winter rest and the recovery in late winter-spring, the most important production begins from March to September.
The June-bearing varieties (very early with a short day) are transplanted from July to September and the harvest is spring.
It is good practice to administer fertilizers with fertigation, with shorter or shorter weekly shifts, using a concentration of the nutrient solution of 1.0-1.5 per thousand.

Soilless cultivation

Soilless cultivation involves the distribution of water and fertilizer several times a day. Fertilizers are dissolved in the water and their concentration is assessed by measuring the Electrical Conductivity (EC) which varies as a direct function of the concentration of nutrients dissolved in the water.
In an above-ground culture, the distribution system of the nutrient solution represents the central core of the system, in fact, it ensures the solution and distribution of the exact amount of fertilizer in the irrigation water. The filtering system is extremely important since small impurities can obstruct the drip system, with irreversible consequences on the plants.
The success of soilless cultivation (in particular for strawberry cultivation) is closely linked to the analytical quality of the water. It must have an EC not exceeding 900-1,000 microS / cm at 25 ° C. Strawberry is particularly sensitive to salinity. In fact, it reacts quickly to different feeding conditions.
In soilless soil to have an optimal growth and production of plants, a correct and balanced nutrition in nutrients is required. Mineral fertilizers containing calcium and iron in concentrated solution precipitate in the presence of phosphates and sulphates, therefore it is important not to mix these elements together, using two separate tanks A and B. While in a third tank C nitric acid will be placed.
The amount of ammonia nitrogen is very low or absent. The electrical conductivity must be low, 1.2 / 1.3 mS / cm from the 2nd / 5th week until the first flowering; 1.5mS / cm from flowering to fruit set; 1.2 / 1.5 mS / cm after fruit set. It can increase during the fruit swelling and harvesting phase, in order to maintain a conductivity of the solution in the root cultivation substrate close to 1.8-2.0 mS / cm.

Irrigation

Considering that the strawberry has a superficial root system, it has intense respiratory activity and high production, frequent watering is necessary. Without irrigation it is not possible to grow strawberries economically.
Insufficient humidity conditions also interfere with plant nutrition, reducing the absorption of phosphorus and potassium. The seasonal irrigation volume in the greenhouse varies greatly, is between 3,000 and 6,000 cubic meters of water per hectare.