Potassium is particularly important in terms of berry quality providing a high sugar and acid content, and a good taste to the fruit. It is important for transpiration and regulates stomatal opening and closing, helping improve water use efficiency particularly in periods of moisture stress.
Potassium is involved in a range of transport and accumulation processes within the plant, including the translocation of nitrates and activation of some enzymes. It 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.
Key quality characteristics such as fruit acidity and TSS continue to rise with levels of potassium up to 535 lb K2O/ac and beyond. Potassium also influences the levels of vitamin C within the fruit and has a direct effect on anthocyanin levels, improving berry color. Rate of K use needs to be balanced by that of nitrogen and adjusted according to growth stage of the crop. See figures above.
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 sulfate 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. See figures above.