T-Sum is the key to N effectiveness

Farmers planning early season nitrogen applications would be well advised to take a look at next week’s Livestock section, in which this year’s first Kemira GrowHow T-Sum map will appear.

The objective of T-Sum is to provide grassland farmers with precise information on how to improve the efficiency of nitrogen fertiliser use.

It has been developed to predict optimum timing for early nitrogen applications and, with increasing pressure on farmers to apply only when critical for plant growth, T-Sum can guarantee some certainty of optimum application.

T-Sum is a measure of the cumulative air temperature over time.

Beginning on 1 January, mean daily air temperatures are recorded and continually added to a running total to achieve a cumulative result.

When this total reaches 200, the T-Sum target has been achieved and this is the date at which grass will respond most efficiently to nitrogen.

This measure works because, as air and soil temperatures rise, biological activity within soil increases, providing grass growth benefits from the application of nitrogen fertiliser.

However, this figure on its own is no guarantee of optimum timing and all application plans should pay particular heed to ground and crop conditions.

Generally the first area to reach T-Sum 200 is the south-west, where many areas have already passed the 60 mark.

As the weather improves, so it progresses up the country.


Looking ahead, unsettled weather is likely for all parts of the UK in the next few weeks, says Stuart Bennett of ADAS.

“T-Sum values will continue to increase rapidly as temperatures remain mild.

“Temperatures will then return to normal around the middle of the period and expect T-Sum values to slow as a result.

“The Hebrides and the south and south-west coast will have reached T-200 by the end of this month.”