Phosphorus

A major plant nutrient which is represented by the chemical symbol P. It is a component of nucleic acids, of DNA and RNA, and energy transfer in respiration and photosynthesis, with energy for example being supplied by ATP, and is also required for seed production.

Phosphorus typically forms the fourth highest percentage of any plant nutrient (excluding carbon, hydrogen and oxygen) within a turfgrass leaf, with a typical dry matter mid-range concentration being around 0.3%.

Phosphorus deficiency, which will be uncommon in many turfgrass situations, can result in reduced cell division and growth, a darker green appearance (bluish-green, with a purple tinge of leaf margins) to leaves due to continued chlorophyll production which is concentrated in a lesser volume of leaf area from reduced leaf growth extension. Mature leaves will be the first to show deficiency symptoms.

An increase in the ratio of stored carbohydrates (as a proportion of shoot to root distribution of these compounds) to the roots will also occur where a deficiency arises. Sward thinning can occur due to a lack of available phosphorus and this will provide space into which weeds can become established.

This nutrient is particularly required for optimum seedling germination and the initial development of young plants and is therefore routinely applied as a pre-seeding fertiliser. When applied as a fertiliser phosphorus is also initially readily available to a plant, but soon becomes less soluble and less available. It is frequently over applied to turf surfaces, and in such circumstance, this encourages shallower rooting and also increased competition from undesirable annual meadow grass which can seed prolifically throughout the year and white clover.

Soils can contain phosphorus in many forms: in acid soils it can readily be contained in the compounds of aluminium phosphate (AlPO4) and iron phosphate (FePO4); whilst in near neutral (pH 6.5 and above) to alkaline soils it can be predominantly contained in the calcium phosphate (CaPO4) compound. Phosphorus is fairly insoluble in these compounds and is only slowly weathered within the rootzone to be made available within the soil solution to plants.