Do you add urea to your fertiliser, sure it’ll make it green for a bit – but it’ll get hungry. Lets take a look at Nitrogen.

Nitrogen in the soil is the most important element for plant development. It is required in large amounts and must be added to the soil to avoid a deficiency. Nitrogen is a major part of chlorophyll and the green color of plants. It is responsible for lush, vigorous growth and the development of a dense, attractive lawn. Although nitrogen is the most abundant element in our atmosphere, plants can’t use it until it is naturally processed in the soil or added as fertilizer.

To much or not enough Nitrogen

An excess of nitrogen, caused by fertiliser over-application, can result in rapid, lush growth and a diminished root system. In extreme cases, too much quick-release nitrogen can cause burning of the leaf tissue and plant death. A lawn with a nitrogen deficiency will lose its green color and begin to turn yellow.

The Nitrogen Cycle

Nitrogen can go through many transformations in the soil. These transformations are often grouped into a system called the nitrogen cycle, which can be presented in varying degrees of complexity. The nitrogen cycle is appropriate for understanding nutrient and fertiliser management. Because microorganisms are responsible for most of these processes, they occur very slowly, if at all, when soil temperatures are below 15 degrees, but their rates increase rapidly as soils become warmer.

So where does Nitrogen come from?

Organic Sources:

  • manures
  • activated sewer sludge
  • other natural products like compost teas, fish meal, and guano

Organic or naturally occurring nitrogen is the by-product of microorganisms breaking down organic matter. The process is a slow and extended release with no danger of leaching. Organic fertilisers have a very low burn potential so there is no risk of plant injury from over application. Using organic sources of nitrogen builds a healthy soil rather than only feeding the plant.

Inorganic Sources:

  • ammonium nitrate
  • calcium nitrate
  • ammonium sulfate

Inorganic nitrogen comes from mineral sources and is bound to other chemical combinations. It is water-soluble, allowing it to be immediately available to the plant upon watering it. Using inorganic nitrogen allows for quick results, but also has a very high burn potential if over applied. Nitrates also leach through the soil rapidly and unused amounts can contaminate groundwater, so there is a substantial risk in using inorganic nitrogen.

Synthetic Sources:

  • Sulfur-coated urea
  • Resin-coated urea

Synthetic nitrogen is primarily in the form of urea or urea solutions. Alone, urea has quick-release properties but it can be processed and combined with other materials to be slow release. A coating is applied to the urea, allowing for a slow release based on the thickness of the coating, temperature, and soil moisture.

Many fertilisers will contain a blend of nitrogen sources for both quick green up, and an extended, slow release feeding. The ratio or percentage, of each nitrogen source, is located on the label.

So what do you do if you apply to much nitrogen?

If you notice that your regular fertilising isn’t having the same growth and greening effects, and you have been applying extra Urea to your fertiliser chances are you’ve affected the pH levels of your soil, the best thing to do is perform a pH test – you can find out more info on pH tests and the results here

There is a saying that we use when extra urea is added to a fertiliser – it is ‘your lawn is going to be hungry’ meaning that when you apply the normal levels of NPK fertiliser you lawn always wants more.