TOP DRESSING
Understanding Nitrogen Sources for Effective Winter Fertiliser Application
By Kelly-Marie Clack, UK Technical Manager, Origin Amenity Solutions
hoosing the right
C fertiliser in the winter months can be challenging, so it’ s important to understand your specific goals before application.
It is not about the analysis on the bag, but the nitrogen sources used to make the analysis.
A fertiliser analysis of 6.5.18, applied at 35g / m2 will provide 21kg of nitrogen per ha. To understand how the turf is going to respond we need to know the nitrogen sources used.
Nitrate and Ammonium nitrogen will provide a quick and visible turf response. Improved growth, vigour, colour and sward density is often observed.
Urea or Organic nitrogen will take longer to respond as they need to be changed in the soil to be made plant available.
In early spring, when soil temperatures are still low, soil microbes are less active and cannot effectively break down nitrogen into plant-available forms. Therefore, it’ s essential to know which nitrogen sources in your fertiliser are immediately available to plants and what kind of turf response you can expect after application.
Plants absorb nitrogen through their roots in a soluble form, either as ammonium( NH 4
+
) or nitrate
( NO 3-
). These are considered plant-available forms of nitrogen, meaning fertilisers containing them typically produce a quick turf response.
If ammonium is not immediately taken up by the plant, it can remain in the soil’ s cation exchange sites( CEC) until needed for growth, or it may undergo nitrification. During this process, Nitrosomonas bacteria convert ammonium into nitrite( NO 2-
), and Nitrobacter bacteria then convert nitrite into nitrate- a form readily available to plants. However, this process also depends on sufficient soil temperature.
Organic fertilisers and soil organic matter must first undergo mineralisation, where soil microbes break down organic nitrogen into ammonium that plants can then use for growth. For mineralisation to occur, soil temperatures must be above 5 ° C. Similarly, urea-based fertilisers rely on urease enzymes to convert urea into ammonium.
Because these nitrogen sources require transformation before plants can use them, the turf’ s growth response is slower, with minimal immediate visual impact compared to using directly available nitrogen forms.
A question always asked is how much nitrogen should I apply?
There is no simple answer to this question however, visual assessment and data collection can provide guidance to this:
Assess growth, colour and response to play and stress. Insufficient nitrogen will lead to yellow and stunted growth. Turf is then left susceptible to turfgrass diseases and pests.
Measure clip volume to have a better understanding of when your turf requires a nitrogen input. You want turf growth to recover from play and no more to achieve optimum performance and plant health.
Monitor the weather forecast and understand what impacts this has on your surfaces, for example, on sand-based constructions the CEC is likely to be low therefore heavy rain could lead to leaching of nutrients and further nitrogen inputs may be required.
Take soil samples and trends the results over time to understand what impact your fertiliser input is having on your soil chemistry. Soil moisture balance is important for soil and plant health, stress management and nutrient uptake. Surfaces need to meet the visual requirements and expectations of the turf managers, and the performance needs to meet the expectations of players. Whilst trying to look after our environments in a responsible and sustainable manner.
Many products will contain a variety of nitrogen sources formulated together to provide a consistent release of nutrients. Nitrates, ammonium, urea, methylene urea and resin coated, controlled release urea; can be incorporated to produce products tailored to turf manager’ s requirements. Whether it’ s a cold temperature growth response, recovery from wear damage or to promote resilience through periods of high stress, these formulated products enable turf managers to select the product most suited to their needs. For tailored advice on fertiliser selection and nutrient management through the colder months, contact the technical team at Origin Amenity Solutions on 0800 138 7222 or email sales @ originamenity. com
40 GroundskeepingJournal. co. uk | November / December 2026