Nitrogen

A major plant nutrient which is represented by the chemical symbol N. It is the major element in the atmosphere at about 78% by volume; but this is unavailable to plants in this form.

It is a component of many plant constituents, including amino acids, proteins, nucleic acid (DNA), the chlorophyll molecule, being involved in photosynthesis. Nitrogen forms the 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 3%.

Nitrogen is the main nutrient that is applied to a turf surface, and it also has the most impact on leaf growth - both vertically and tillering for sward density, it significantly influences greenness of leaf, and also contributes to the overall health and durability of a sward, aiding recovery from wear, as well as a plant’s ability to reduce susceptibility to disease attack and infection.

High application rates of nitrogen will force grass to grow rapidly, but this will result in a weak turf, because soft sappy growth will be produced, and this makes the turf more susceptible to disease and pest attack. A softer turf is also produced with excessive applications of nitrogen.

Increasing levels of nitrogen will also produce a reduced branching of roots and increase leaf growth at the expense and reduction of root growth. Where roots encounter local pockets of nitrogen, for example where a fertiliser application has not been uniformly applied, they will produce a well-branched lateral root system, which could in effect result in a layering of root systems within a soil profile.

Nitrate (NO3) is the main form of inorganic nitrogen taken up by grasses, being very soluble and can be more readily take up in warmer temperatures, along with Ammonium (NH4), which can be more readily taken at cooler temperatures. Where it is stored in organic compounds and structures within a plant any applied nitrogen will be reduced to ammonium beforehand.

Plants growing in very acidic, as well as very wet, soils, will often have preference of taking up nitrogen as ammonium, and where temperatures are below 5°C only ammonium uptake occurs as nitrate uptake ceases at this temperature.

Nitrogen taken up as ammonium increases soil acidity as hydrogen ions (H+) are exuded into the soil solution by the plant roots. Nitrogen taken up as nitrates can often decrease soil pH as hydrogen ions are more likely to be taken up plants roots from the soil.

Nitrogen deficiency will reduce plant growth, with it becoming stunted where inadequate supplies are present, narrower leaves, yellowing of leaves, and chlorosis, with the latter initially occurring in the older leaves.