# Temperature sum (T-sum)

The temperature sum, or T-sum, is a sum of the average daily temperature above 0˚C degrees from January 1^{st} of that year. The T-sum is widely used in agriculture to determine the nitrogen application at the beginning of the grassland growing season. For grassland, the standard practice is that fertilizing is only done when the temperature sum is between 180 and 250 degrees.

The desired T-sum varies according to the purpose for the grass.

High grass yield:

- For an early pasture cut, fertilizing is recommended at a T-sum between 200 and 250 degrees.
- For a cut with a yield around 3000 kg ds fertilize at a T-sum between 250 and 300 degrees.

High nitrogen utilization:

- For an early pasture cut, fertilize at a T-sum between 250 and 300 degrees.
- Fertilize a corn cut between 300 and 400 degrees.