This forms a bank of phosphate. Nobody seems clear on how large this bank should be. The solid fertiliser companies would like to think it should be large. It is important for the vegetative growth stage of the plant, for photosynthesis, plant root growth, fruit fill and flowering. Clovers are heavy Potassium feeders.
Grasses compete very strongly for Potassium, such as in grass dominated early spring pastures.
Potassium translocates very readily from older leaf to younger growing points. In a Potash deficient soil urine patches have a mixture of grasses and clover but there is little clover elsewhere. Conversely in a nitrogen deficient soil grasses are dominant in the urine patch. The most important function of S is its involvement in protein synthesis. Sulphur is regarded as the fourth major nutrient.