Nutrition of Protected Strawberries

Keywords: Substrate culture, Nutrient solution, Soil mineral nitrogen, K:Ca ratio, Fragaria.

Although nutrient uptake by strawberries can vary for several reasons the absorption of the major elements is very similar (1 N: 0.5 P₂O₅: 1.5 K₂O: 0.5 CaO: 0.2 MgO) for plants grown in soil and on substrate. However, these ratios change during flowering and fruiting as the uptake of K increases.

Generally in soil culture 70 to 120 kg N, 25 to 40 kg P₂O₅, 100 to 140 kg K₂O and 30 to 50 kg MgO are applied per ha. Nitrogen recommendations are based on available soil mineral N and on petiole sap analysis.

In substrate culture a balanced nutrient solution with a pH of 5.5 is used. The electrical conductivity is set at 1.4 mS/cm for ‘June-bearers’ (short season varieties) and at 1.2 mS/cm for ‘ever-bearers’ (long-season varieties). The K:Ca ratio is maintained at 0.65 during vegetative development. During flowering and fruiting a higher K:Ca ration of 0.8 is advised because it improves fruit taste and firmness. During the vegetative phase 5 to 10% of the total N is given as NH₄-N, but none is applied from flowering onwards to avoid acidification of the substrate. Water quality needs special attention for substrate culture. Excessive B, Zn and Na can lead to toxicity and yield reduction. On the other hand Fe and Mn deficiency can occur at high pH levels in the substrate.

Philip Lieten, National Research Centre for Strawberries, Meerle, Belgium.

20 Pages, 6 Tables, 71 References.