Strawberry

Cultivated strawberry (Fragaria × ananassa Duchesne)

It belongs to the Rosaceae family and is a perennial herbaceous plant, but in production scale it is grown as an annual, biennial or triennial to ensure greater production. Today, most cultivated varieties are the result of crosses between Fragaria chiloensis and Fragaria virginiana or between them and other species. The height of the plant is 15-20 cm and its diameter is 20-40 mm. The genus Fragaria consists of herbaceous plants grown for their large red fruits. The strawberry plant has a very high genetic diversity, which allows it to acclimatise to a variety of environments. It is a plant that is adaptable to a wide range of soils, light sandy loam soils being considered ideal. However, rational nutrition and balanced irrigation are factors which have a significant influence on its growth.

Strawberries have been cultivated for thousands of years for their delicious fruit. It is a plant known since ancient times as the chamomile plant. Its fruit is a rich source of energy (46 kcal/100g) and is rich in vitamin C and antioxidants, essential for the health of the immune system and skin.

Strawberry is cultivated on a large area in Greece, mainly in the Regional Compartments of Achaia and Ilia (20 000 ha, 2022) with an average yield of 4-5 tn/stremma.

Adaptability

Strawberry is a highly adaptable plant and this is due, as mentioned above, to the fact that it is a hybrid of two very different species.

The soil type has a decisive influence on the plant’s diversity. Strawberries grow well in a wide range of soils, but perform significantly better in sandy loam (SL). Strawberry plants prefer slightly acidic soils, with a pH of 5,8-6,5. Where there is sufficient organic matter, they grow in a pH range of 5,0 to 7,0. Strawberry is a moderately salinity-sensitive crop (maximum 3 dS/m and optimum = 1.5 dS/m). Increased salinity in the rhizosphere significantly reduces the development of the root system, the growth rate of the plant and the uptake of water and nutrients.

It is important to avoid poorly drained soils as well as stony soils. Strawberries are demanding in terms of soil moisture and during the growing season they need 600-900 m³ of water per acre. Its drought tolerance is very low as it needs soils with high water capacity.

Like many temperate zone species, strawberries develop a state of lethargy in autumn which they overcome with the low temperatures of winter. Strawberries need temperatures of 8 to 15 °C to germinate. In the greenhouse, the optimum soil temperature ranges from 12 to 15^oC, the optimum daytime temperature is 16 to 22^oC and at night 10 to 13^oC.

For excellent growth and maximum utilisation of the genetic potential of strawberries, it is necessary to meet their nutritional requirements at the right stage and in the ideal quantity-ratio.

Particular characteristics

Rational nutrition of the strawberry crop is one of the most effective ways to increase its growth and productivity. A rational nutrition program should aim to optimise inputs, increase quality yield, while protecting the environment, soil fertility and crop viability.

The phenological stages of strawberry development are divided into the following (BBCH Meier et al., 1994):

Sprouting and differentiation of flower buds
Foliage development (1-9 compound leaves)
Development of stolons and formation of young plants
Emergence of first flowers from the base of the rosette
Flowering (from the opening of the first flower to the ripening and falling of the petals)
Fruiting (the first achenes start to become visible)
Maturation of the fruit. The colour change in flowering plant changes from green → white → white- pink → pink → red → deep red or crimson (overripe)
Ageing/ onset of Lethargy

Nutrition products applied according to the following principle., appropriate quantity, appropriate application timing at the right phenological stage, appropriate type and appropriate application method, enhance important cultural factors such as development of flower buds, load-germination balance, enhancement of photosynthetic activity and adequate coverage of nutrient requirements.

However, before applying fertilisers, it is recommended that both the physico-chemical properties of the soil and the results of the foliar diagnostic analysis are known precisely.

Top-dressing Applications

In the early stages of strawberry cultivation, i.e., at transplanting, the use of Phosphate Fertilizers is recommended to establish a strong root system. During the start of germination and until the beginning of fruiting, it is necessary to apply Balanced Fertiliser every 15 days. One month after transplanting, we start the application of Trace Elements as well as Calcium and Magnesium. At the beginning of fruiting, the crop is strengthened with the use of Potassium Fertilizer.

Foliar applications

The foliar applications of strawberry fertilisation complement the surface application, mainly aimed at improving the flowering and fruiting processes. These stages are considered crucial for the production and quality of strawberry fruit.

The use of growth regulators such as amino acids, plant hormones and algae extracts is essential to improve hormonal balance, reduce abiotic stress and improve nutrient assimilation. The aim is to enhance flowering, fruiting and fruiting and thus production.

Nutrient requirements

Nitrogen (N), Phosphorus (P₂O₅), Potassium (K₂O), Calcium (Ca), Magnesium (MgO), Iron (Fe), Zinc (Zn) and Boron (B) are the main nutrients required for strawberries.

Of the macronutrients, most critical are:

Nitrogen (N): is one of the most important nutrients for strawberries, essential for germination and production. As a central component of amino acids, which are the building blocks of all proteins, N stimulates the vegetative growth of leaves and shoots. Lack of N at critical stages leads to discoloration of older leaves, reduced flowering and fruit set.

Phosphorus (P₂O₅): an equally important macronutrient as it is responsible for cell division and energy management in the plant (ADP-ATP). Available Phosphorus is essential in the transplanting stages as it contributes to the establishment of a strong root system.

Potassium (K₂O): an essential nutrient for many physiological processes in strawberry cultivation, such as the regulation of cell osmotic potential and the activation of enzymes involved in photosynthesis, transpiration and respiration. Sufficient Potassium nutrition ensures resistance to abiotic stresses. In addition, it influences the physiological, quality and organoleptic characteristics of the fruit, which is why it is widely known as a ‘quality nutrient’. Its deficiency directly reduces production and adversely affects the quality of the harvested fruit.

Calcium (Ca): This is an important nutrient for strawberry cultivation as it causes intense cell division during the fruit setting stage, resulting in an increase in fruit size. As a rule, it contributes to an increase in the production of pigments (anthocyanins) in the fruit, giving a more uniform and intense colouring of the fruit produced more quickly.

Magnesium (MgO): a critical nutrient for the photosynthesis process as it is a component of chlorophyll, contributing in addition to protein synthesis and phosphorus transport. Mg moves through the vascular tissues of the phloem, so its deficiency will first appear in old leaves, showing a pale green or yellow colour between the nerves.

Of the micronutrients, most critical are:

Iron (Fe): an essential component for the synthesis of chlorophyll. It takes part in the redox reactions of respiration and photosynthesis and contributes synergistically to the process of nitrogen fixation. Its deficiency appears in a characteristic pattern where the ribs remain green while the leaf is yellow.

Zinc (Zn): its contribution is quite significant as it is involved in several metabolic processes in strawberries, playing an important role in the synthesis of tryptophan, a precursor of auxin (IAA). It contributes to the load-growth balance and has fungistatic effects.

Boron (B): Stimulates cell division and acts as a water regulator. Its deficiency affects pollen tube germination and consequently fruit setting. It is important to follow the recommended dosages as strawberries are sensitive to boron deficiency and sensitive to excess boron which can cause phytotoxicity.

Nutritional requirements of strawberries

Main nutrients to be supplemented in kg/stremma

Nitrogen

(N) 10,8 kg
Phosphorus

(P2O5) 7 kg
Potassium

(K2O) 19 kg

Crop Recommendation Program

The doses and growth stages are indicative and are always adjusted according to the recommendations of the agricultural engineer. Because rational fertilisation is always assessed in relation to:

Expected yield
Soil characteristics
Planting density
Environmental conditions
Growth stage
Plant vigour
Growing duration
Variety

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