Looking for pastures NUE

Researchers from Teagasc, University College Cork and University College Dublin have come together to reduce the output of ammonia, nitrous oxide and nitrate emissions from grazing dairy cows.

Despite the positive effect nitrogen fertiliser use has on agriculture production, it is poorly utilised. Due to the high nitrogen requirement of perennial ryegrass (PRG), excessive amounts of nitrogen relative to the animals’ demand can accumulate in the sward.

Farm gate nitrogen balance and nitrogen use efficiency (NUE) are the two most widely used indicators of nitrogen efficiency in pasture-based systems. Animals consuming such swards typically exhibit low NUE, contributing to environmental challenges such as ammonia and nitrous oxide emissions and nitrate leaching into groundwater.

PASTURE-NUE – a collaborative project between Teagasc, University College Cork and University College Dublin – is actively exploring how the agricultural industry can improve management practices to mitigate the current trade-offs between the production of agricultural goods and environmental sustainability. It will quantitatively measure the NUE and environmental footprint of various pasture-based diets, and highlight dietary strategies with the greatest potential to abate nitrogen emissions.

Plantain’s role in supporting white clover

PRG-based systems require 200–300kg of nitrogen input per hectare to maintain productive growth rates of high-quality pasture. The incorporation of the biological nitrogen fixation capability of leguminous plants – those that can convert nitrogen gas into a usable form for plants – will be imperative to ensure the economic sustainability of farms. This will also maintain Ireland’s ability to produce nutritionally superior dairy products from home-grown pasture.

The inclusion of white clover (WC) into PRG swards can increase the milk production efficiency of lactating dairy cows while simultaneously reducing the amount of chemical nitrogen fertiliser required. Furthermore, PRG-WC swards increase the farm gate NUE compared with PRG-only swards.

The issue, however, is that as a system’s total nitrogen inputs increase, there is an exponential rise in the amount of nitrogen that can be leached, regardless of where the nitrogen input comes from.

Plantain, a forage herb, has been shown to complement PRG-WC swards by further increasing milk production efficiency while reducing the risk of nitrogen leaching and nitrous oxide emissions. In a series of experiments in New Zealand, the inclusion of plantain was demonstrated to increase the overall NUE of lactating dairy cows, partition a greater proportion of the excreted nitrogen into faeces rather than urine and alter the animal’s urinary physiology, resulting in waste with a lower nitrogen concentration.

Testing the benefits of plantain

Recent research in Teagasc, where researchers conducted a grazing plot study over two years investigating plantain inclusion, showed that PRG-WC-plantain swards achieved higher dry matter production (crucial for livestock’s health and production) when compared to PRG-WC swards. Furthermore, at the end of the experiment the plantain still contributed substantially to the sward’s dry matter production. Due to the numerous benefits plantain could offer, it is critical that such swards are further evaluated under Irish conditions.

Researchers at both Teagasc Moorepark and University College Dublin are performing a number of total nitrogen collection studies to accurately quantify the nitrogen loss abatement potential of swards containing white clover and plantain. These experiments involve mass balance experimental techniques, whereby all animal inputs (i.e. feed) and outputs (i.e. milk, urine and faeces) are weighed and analysed to accurately determine NUE.

Researchers at Teagasc Johnstown Castle will then incorporate the waste material into its studies to fully quantify the environmental nitrogen emissions from cows consuming such swards. Drone imagery (to identify urine and dung patches) will be used for the purpose of upscaling fluxes from single or simulated point sources to the paddock level, to quantify grazing systems’ emissions factors.

The outcomes of these experiments will be used to derive new nitrogen emission factors to increase accuracy when determining the contribution from grazing animals to the national nitrogen emissions inventories.

Strategic supplementation

In periods of inadequate grass supply, additional dietary strategies exist to improve the NUE of pasture-based systems, such as low nitrogen strategic supplementation and the incorporation of complementary feed additives. To understand if such strategies would be beneficial across the country, PASTURE-NUE is engaging with 28 commercial farms as part of an ‘on-farm’ sampling programme.

This programme will develop a national database on the chemical composition of pasture and supplemental feeds across multiple years, as well as tools capable of rapid chemical composition determination and dissemination. From this, new strategic supplementation programmes will be designed. The efficacy of these programmes to increase the NUE of pasture-fed cows will be evaluated in large randomised controlled studies.

Finally, comprehensive characterisation of the dairy products produced from these dietary strategies, as well as from the white clover and plantain swards, will be performed by University College Cork to ensure the superior attributes of ‘pasture-fed’ products are maintained.

As the knowledge outcomes from PASTURE-NUE are captured in a data centric manner, stakeholders such as regulators and policy makers will be able to implement the outcomes of this project into environmental modelling and national inventory calculations. Ultimately, PASTURE-NUE will increase the efficiency of nitrogen utilisation in pasture-based systems, preventing or diminishing the unwanted impact of nitrogen on the environment. 

20%

less fertiliser must be used within agriculture by 2030, according to EU targets.

FUNDING

This project is funded by the Department of Agriculture, Food and the Marine’s Competitive Research Funding Programme.

Contributors

Michael Dineen

PASTURE-NUE Principal Investigator; Research Officer
Grassland Science Research Department, Teagasc Animal & Grassland Research and Innovation Centre, Co. Cork

Brian McCarthy

Research Officer
Grassland Science Research Department, Teagasc Animal & Grassland Research and Innovation Centre, Co. Cork.

[pic cap 1] L-R Michael Dineen, Eoin Wims, Robert Serem, David Flynn and Matthieu Fort performing a total nitrogen collection study

[pic cap 2] PhD student Chris Heffernan collecting pasture samples from a commercial dairy farm