Reducing fertiliser N use to reduce GHG emissions and save costs

Mark Plunkett and Tom O’Dwyer tell us how Teagasc can help you to identify opportunities to reduce GHG emissions on your farm.

Keith Fahy, Teagasc Advisor caught up with Siobhan Kavanagh, Signpost Programme Communications and Engagement Specialist, Teagasc to get an insight as to what is being discussed at the Signpost stand at Ploughing 2022. The main messages at the stand are the three R's: 1 - replace chemical nitrogen; 2 - replace CAN with protected urea; 3 - reuse - optimise the value of your slurry on your farm.

With the EPA highlighting the increased usage of synthetic nitrogen fertilisers as a contributor to the sector’s increased GHG emissions, it makes sense to look at ways to reduce their usage.  This article outlines the four R’s approach to fertiliser use: reduce, recycle, replace and reward.

Step 1

Reduce overall fertiliser N usage, by focussing on soil pH, soil P & K levels, clover and MSS, and improved use of slurry. Liming alone will release up to 70 kg N/ha/year and increase the availability of soil P and applied P. Maintaining optimum soil fertility through a balanced fertiliser programme will improve nitrogen use efficiency (NUE). For example soils with sub optimal soil fertility have a 35% NUE, however optimising soil fertility (Soil pH, P & K Index 3) will increase NUE to 65% offering a major N saving through more efficient use of applied N.  Clover can fix between 80 – 120 kg N/ha/year depending on underlying soil fertility and sward management. Multi-species swards also offer extra benefits in terms of drought resistance and cow health. 

Step 2

Recycle animal slurry and manures. Apply slurry to meet grass N demand under good soil and weather conditions.  Have slurry tested to determine exact N, P & K value and apply with LESS in springtime to maximise N recovery.  A slurry hydrometer can be used to conduct on-farm analysis of slurry. Adjust fertiliser N for slurry N to make fertiliser N savings.
However, in order to reduce GHG emissions following the adoption of the measures mentioned in Steps 1 and 2, N fertiliser application must be decreased by the amount of N that each measure saves, otherwise there is little or no GHG saving.

Step 3

Replace any fertiliser N used with protected urea. Replacing nitrate based fertilisers (CAN / 27’s & 24’s) with an ammonium based fertiliser, such as protected urea or blends such as 18-6-12, will lead to reduced GHG emissions. In addition, replacing straight urea with protected urea, will lead to a reduction in ammonia emissions.

Step 4

Reward – save money. Reduced fertiliser usage will reduce your input costs (although there are the costs of correcting soil pH, P & K levels, incorporating clover in order to maintain sward productivity).  Switching from CAN to protected urea reduces the cost of fertiliser N per kilogram applied.  For example, today protected urea (@ €2.25/kg N) is costing approximately €1/kg N less than CAN (@€3.25/kg N).  Or put another way, you can purchase the same amount of fertiliser N as either 3 tonnes of protected urea (1,380 kg N) or 5 tonnes of CAN (1,350 kg N), but the protected urea option will cost you €1,000 less.