A sustained decline in nitrogen (N) concentration levels in rivers in the Timoleague area of west Cork has been recorded over the last four years by Teagasc’s Agricultural Catchment Programme (ACP).

The results show that N levels in the Timoleague catchment area have reduced by almost 20% between 2019 and 2022, with concentrations falling on a consistent basis.

The findings have been welcomed by farmers who argue that changed management practices around fertiliser usage and slurry spreading can work if given the time.

Marked reduction

The Timoleague study found that N concentration levels dropped from a high of 7.15mg/l in 2019 to 6.30mg/l in 2020. This marked reduction continued in 2021 and 2022, with levels dropping to 5.43mg/l and 4.95mg/l respectively.

The 4.95mg/l recorded in 2022 was the lowest N concentration level logged for Timoleague since the ACP started in 2010. The level of N concentration for 2010 was 5.0mg/l.

The ACP results for Timoleague were included in a Teagasc study entitled ‘The Impact of Nitrogen Management Strategies Within Grass Based Dairy Systems’ which was published last week.

The reduction illustrated the positive impact of changed farm management practices

Researchers working on the ACP said the results from Timoleague were encouraging from a farming perspective, given that cow numbers in the catchment had increased in line with national trends.

The reduction illustrated the positive impact of changed farm management practices, researchers maintained.

One of the main changes implemented by farmers in Timoleague in recent years has been a more strategic approach to the spreading of fertiliser and slurry.

Grass growth

The application of fertiliser is increasingly being tailored around grass growth, with better utilisation of slurry also helping.

However, researchers conceded that outside considerations were also a factor in the sharp decline in N concentrations.

It was pointed out that the very high N concentrations recorded in 2019 were heavily influenced by the drought conditions of 2018 and particularly by the high usage of fertiliser in the back end of that year.

Conversely, the low N concentrations recorded last year were influenced by the reduced usage of fertiliser on farms in 2022 due to soaring prices.

The recently published Teagasc study maintained the Timoleague results confirmed that cow numbers and stocking rates were not the primary drivers of N concentrations in groundwater and rivers.

Important factors

It pointed out that the physical characteristics of catchment areas, meteorological conditions and agronomic practices were equally important factors.

Worryingly, the report conceded that N concentrations remained well above the 2.6mg/l target set by the Environmental Protection Agency.

It also accepted that significant work remained to be done to improve water quality in rivers across the south and east.

The most challenging rivers are the Slaney, Nore, Bandon and Boyne catchments, with improvements also needed in the Blackwater, Deel, Dodder, Lee, Liffey, Maigue, Suir and Tolka catchments.