The aim of fertilising is to produce a vigorous sward of grass, or more properly, a grass that has a vigorous root system to at least 100mm in to the soil. The best strategy for turf nutrition is to supply the grass with adequate levels of all nutrients except nitrogen. Growth is then controlled by application of nitrogen in amounts just sufficient to provide an acceptable appearance. High levels of phosphorus are unnecessary and waste money. Phosphorus stimulates grasses into producing seed - the last thing that is wanted in a lawn.
Excessive phosphorus causes potassium imbalance and stunting of root growth.
Fescues dislike quite small amounts of phosphorus and die out as the phosphorus level in the soil increases. Potassium is an essential nutrient, valuable for turf because it toughens the leaves so that they are more wear and disease resistant. It promotes the storage of carbohydrates in the roots, and has an essential role in regulating water loss through transpiration. Extra potassium applied in autumn when the grass is going into dormancy will help it survive through winter and enhance its ability to grow quickly in spring. Iron is the trace element most often in short supply in turf.