What growth response can I expect from spreading nitrogen this autumn?

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. With this, spreading nitrogen (N) this autumn is worth considering.

Grazed grass is the cheapest feed and suckler beef farmers must maximise the length of the grazing season. However, some regions in Ireland – especially in the south and south-east – are still experiencing low grass growth rates.

Recently, the Minister for Agriculture Micheal Creed extended the period for which chemical fertiliser can be spread; the closing date for chemical application is now, September 30, 2018.

Although the growth response to N fertiliser in autumn is best described as modest, with this extension, there is an opportunity to extend grass growth – especially when ground temperatures remain on the high side and conditions are favourable.

In addition, with lower supplies of fodder and spiralling feed costs, the opportunity to maximise grass availability is vitally important.

Teagasc estimates the average response to every 1kg of 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.

Source: Teagasc

The grass growth response to the nitrogen 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?

Teagasc estimates the value of autumn grass at approximately 11c/kg of DM (from Pasture Profit Index model). The average cost – Teagasc says – of 1kg of CAN is approximately €1. With this, a growth response of 9-10kg is required to break even.

Therefore, according to Teagasc, the cost and availability of feeds other than grass now make N fertiliser application more economical because the value of autumn grass will rise a lot closer to 15-20c/kg of grass DM than the standard 11c/kg of grass DM.

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