What grass growth response can I expect from spreading nitrogen this month?

It is well documented that every blade of grass that an animal eats represents a saving on winter feed costs and will have a positive impact on its live-weight gain.

Grazed grass is the cheapest feed and suckler beef farmers must maximise the length of the grazing season (weather permitting); the opportunity to maximise grass availability is vitally important – especially when ground temperatures remain on the high side and conditions are favourable.

However, each individual farm is different and stocking rates vary on every farm, but for the most part drystock farms are lower than dairy operations.

By knowing the number of days ahead in the rotation, farmers will know if they have enough grass built for the autumn. Teagasc recommends that stretching the rotation is the best way to achieve this.

Source: Teagasc

For the most part and in most regions, grass growth this year has been good, and there is plenty of grass available on farms. With this in mind, some farmers may question when is the best time to go out with the last round of fertiliser.

Teagasc research estimates the average response to every 1kg of nitrogen (N) applied – during early August, early September and early October – in the graph below. Approximately 30kg of N/ha (24 units of N/ac) was applied to test response levels.

The grass growth response to the N application in early August was 27kg of DM (dry matter) per kilogram of N. In September, 19kg of DM per kilogram of N was achieved.

Naturally, the lowest response was in October, when a growth response of 10kg of DM per kilogram of N was recorded.

What does this imply?

From the above figures, farmers can grow almost 1.5 times more grass when N is spread in August rather than September.

For example, if we take a farm – with a stocking rate of 2.5LU/ha – and spread 30kg of N/ha, taking a growth response of 27kg of DM/kg of N applied, this results in 810kg of DM/ha of grass or 20 days grazing/cow.

stamp duty weather beef

However, again taking a farm with a stocking rate of 2.5LU/ha, but applying 30kg of N/ha in September, this will result in 570kg of DM/ha (30kg of N X 19kg of DM/ha) or 14 days grazing/cow.

Teagasc estimates that every day at grass in autumn is worth €1.80/cow at a stocking rate of 2.5LU/ha. This, Teagasc says, is a difference of €27/ha when fertiliser is applied in August rather than September; on a 30ha farm, it is worth €810.

Remember, the prohibited application period for chemical fertiliser starts on September 15.

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