Definition

The temperature sum (T-sum) is the cumulative total of average daily temperatures above 0°C, calculated from 1 January of the current year. It is widely used in agriculture as an indicator for the timing of nitrogen fertilisation at the start of the grassland growing season.

Importance

Applying nitrogen at the correct T-sum ensures:

• Optimal grass growth
• Efficient nitrogen utilisation
• Reduced risk of nutrient losses

For grassland, fertilisation typically begins when the T-sum reaches 180–250°C.

Recommended T-sum values

The ideal T-sum depends on the production goal:

High grass yield

• Early pasture cut: Fertilise at 200–250°C
• Cut with approx. 3,000 kg dry matter yield: Fertilise at 250–300°C

High nitrogen utilisation

• Early pasture cut: Fertilise at 250–300°C
• Maize cut: Fertilise at 300–400°C

Key considerations

• Monitor daily temperatures from January to calculate T-sum accurately.
• Adjust fertilisation timing based on crop type and yield objectives.
• Avoid early fertilisation before the recommended T-sum to prevent nutrient losses.