On grassland farms, having enough grass available for livestock to graze is crucial to ensuring a profitable enterprise, Teagasc notes.

The research authority has launched five ‘factsheets’ advising farmers on how to improve and maintain water quality in and around their farms, to coincide with Teagasc Water Quality Week.

One of these factsheets deals with early nitrogen in spring grassland. In springtime, applying nitrogen (N) fertiliser will help to provide enough grass as livestock are turned out from winter housing.

Key decisions

Key decisions to ensuring sufficient supply of grass are the timing and rate of fertiliser N application. The challenges lies with achieving “maximum returns” from applied fertiliser N, without there being negative impacts on water quality, Teagasc says.

Nitrate in the soil “is both soluble and mobile”. In free draining soils, nitrate loss can occur when available nitrate in the soil, that is not recovered during grass growth in spring or autumn, is removed by percolating water.

Teagasc notes that if soils become saturated or are subjected to heavy rainfall, this nitrate is more likely to leach down through the soil profile. Once nitrate travels below the root zone, it will be lost to groundwater where it can have a negative impact on water quality.

Early spring and autumn/winter are the times of the year with highest risk of nitrate leaching, due to grass growth rates being low and rainfall levels at their highest. Any nitrate applied during these conditions is “at greater risk of leaching and careful application of fertiliser N is critical to reduce this risk”.

Benefits of improved spring nitrogen

According to Teagasc, the benefits of improved spring nitrogen use are:
  • N applied in suitable conditions will help improve nitrogen use efficiency;
  • Better grass growth response to nutrient applied;
  • Reduction in the level of nitrate leached to groundwater;
  • Reduced negative impact on water quality;
  • Improved financial return from fertiliser investment;
  • Potential to reduce fertiliser N rate required and reduce fertiliser costs on farms.

Tips when applying early spring nitrogen

When applying early spring nitrogen, Teagasc advises to only spread if fields are suitable for tractor work, when water is drained sufficiently and where heavy rainfall is not forecast.

The advice is as follows:

“Apply fertiliser N when soil temperature is greater than 6° and rising. Typically, this occurs around the end of February however, this will vary across the country and from year-to-year.

“Target fields for early N that are most likely to respond to an early N application: fields at optimum soil fertility [pH, P and K]; perennial ryegrass swards; recently reseeded or with a grass cover of greater than 400kg DM/ha or 5cm grass.

Match chemical N applied to grass growth rates as this varies across the country. Apply up to 30kg N/ha [24 units N/ha] maximum in first split and avoid fields that have received an application of cattle slurry

“To ensure efficient and accurate application of fertiliser, calibrate fertiliser spreaders and use GPS equipment where available. Use protected urea for early N applications as this will help reduce the risk of nitrate leaching.”

The factsheet, which is available through the Teagasc website, contains further information on nitrate leaching risks and protected urea.