FEWER COLD spells and more warm ones means this year’s Kemira GrowHow T-Sum season has made rapid progress, with values surging forward throughout the country.

According to reports from the ADAS Met Office Rural Environment Team, temperatures exceeded normal by up to 5C across the country in the second week in January. This sets the scene for another early season, says head of its team Ian Barrie.

“By Jan 17, T-sum values had exceeded 100 in the southern and western fringes of England and Wales. Central areas of England and Scotland stand at 80 and 35-50 degree days, respectively,” he reports.

In the 16 years, Kemira GrowHow has calculated T-Sum, the earliest average date for the UK reaching T-Sum was Feb 2. However, in the latest spring during recording much of Scotland only reached T-Sum 200 in April. Last year some of southern England and the south west had reached T-Sum 200 by Feb 1, whereas for some of northern Scotland it wasn’t achieved until after Mar 8.


 T-Sum provides grassland producers with up-to-date information on how to get the best out of nitrogen fertiliser. It’s designed to predict the optimum timing for first nitrogen applications, explains Kemira GrowHow agronomist Allison Grundy.

“T-Sum measures the cumulative air temperature over time. Starting on Jan 1, the mean daily air temperatures are recorded by the Met Office from 220 sites and added to a running total. When this reaches 200, the T-Sum target has been achieved,” says Miss Grundy.

This is the date at which grass responds most efficiently to nitrogen applied and, depending on ground and crop conditions, ideally this is when first nitrogen applications should be made.

But even 2-4 weeks after T-Sum 200 is reached, there is a window when nitrogen use efficiency will still be 90% of the optimum, she says. See next week”s and future issues of farmers weekly to see how T-Sum is progressing in your area.

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