Sustainability is the ‘buzz’ word for agriculture in Ireland at present, and becoming more sustainable and increasing efficiency – particularly where nitrogen (N) is concerned – is consistently topical.

Irish agriculture is already quite sustainable, with grass being a basic within our production systems, whether that is dairy, beef or sheep. However, one of the areas that we can improve upon is N use efficiency.

Speaking at a recent Department of Agriculture, Food and the Marine (DAFM) webinar discussing the draft proposal for the Nitrates Action Plan (NAP), Laurence Shalloo, a researcher with Teagasc, outlined research looking into the impact of nitrogen management strategies on the sustainability of grass-based dairy systems.

The research looked at changing the time that fertiliser was applied, along with looking at the level of fertiliser applied.

Non-compliant slurry spreading during the closed period, was also looked at during the research.

Nitrogen leaching

The research determined that the factor that had the biggest impact on nitrate leaching/ha, at a level of 1m, was the weather.

Shalloo noted: “With management practices being the exact same, there was a large variation in nitrates lost – from 39kg to 88kg N/ha from year to year.

“2018 saw a large amount of N leaching due to the weather conditions, when compared to 2010.”

Source: Teagasc

Chemical N

The biggest impact on chemical N loss was also the weather, with 2018 seeing a large amount of leaching compared to 2010 and 2011.

The research also determined that reducing N spread from 250kg/N down to 225kg/N, reduced leaching by 1.4kg/ha or 2.3%.

So, reducing the amount of chemical N spread is reducing loss, but the reduction is less than what was expected.

Increasing the amount of chemical N spread does also increase the amount of leaching that occurs.

Increasing the amount of chemical N spread from 250kg/ha to 300kg/ha increased N leaching by 2.9kg/ha or 4.7%.

Source: Teagasc

Slurry spreading

The research also determined that the spreading of slurry during the closed period also contributed to N leaching.

On a farm where 12% of the slurry was spread during December, N leaching increased from 61.9kg/ha to 65.1kg/ha – or 5.2%.

Shalloo highlighted that, again, there was a significant year to year variation, depending on the weather.

Source: Teagasc

Precision management

Shalloo stated: “This highlighted the need for precision management on farms.

“We can reduce N loss through leaching by reducing chemical N usage during adverse weather conditions, and avoiding the spreading of slurry during the closed period.”