The best quality berries are uniform in size and should be glossy with a strong red color. They should also be juicy and have a strong aroma with no mold or bruises. Variety selection is critical and each cultivar has its own often distinctive shape, size, taste and texture. Fresh strawberries are harvested and stored with the calyx and part of the stem intact, which is then removed by the consumer prior to eating. Size is important, but overly large fruit are more difficult to package and transport.
Small differences in fruit quality can have a strong impact on price and grade, so production methods focus on producing and maintaining good quality fruit with a long shelf life.
Potassium is important for transpiration and regulates stomatal opening and closing, helping improve water use efficiency particularly in periods of moisture stress. It is also involved in a range of transport and accumulation processes within the plant, including the translocation of nitrates and activation of some enzymes.
Vitamin C levels within the fruit are influenced by potassium and it also has a direct effect on anthocyanin levels, improving berry colour.
Key quality characteristics such as fruit acidity and sugar content (TSS) continue to rise with levels of potassium up to 600kg K2O/ha and beyond.
Rate of K use needs to be balanced by that of nitrogen and adjusted according to growth stage of the crop. During vegetative growth around 2.5 times more nitrogen is required than potassium, but during production a molar N:K ratio of 2:1 or 1:1 is more appropriate and will help improve fruit quality.
Similarly, the ratio between potassium and calcium also needs to be in balance to ensure a mix of good fruit taste, fruit strength for a better shelf life and optimum yield. It is also important to recognize that high levels of potassium will not necessarily increase fruit firmness if it restricts calcium uptake.
Strawberries are sensitive to salinity and this makes the use of potassium chloride, with its high salt index, unsuitable for this crop. Yield improves when other potassium forms such as potassium sulphate or potassium nitrate are used.
Potassium can help to reduce the effects of salinity, reducing membrane leakage and helping to maintain fruit quality and reducing yield loss.
Potassium can also help minimize the effects of stresses such as frost by increasing the osmotic potential and therefore lowering the freezing point of the cell solution.