Lime research has positive implications for GHG emissions

Image Credit: Sinéad Mohan

Recently published Teagasc research on the importance of soil pH in reducing grassland GHG emissions signal a win for both policy makers and producers, should farm practices change in accordance with the recommendations. Hannah Woods reports.

With research into liming shining light on potential nitrous oxide emission reduction strategies
emerging from Teagasc in Johnstown Castle, County Wexford, the potential for a more sustainable
future for Irish agriculture lies ahead. The research sets out a plan where, in tandem with liming, an
adequate supply of phosphorus looks to have a major impact on the composition of the microbial
community structure in the soil, while alleviating nitrous oxide emissions. These simultaneously
increase nitrogen uptake and thus lead to increased crop yields.

This new research comes at the perfect time. The recently published Ag Climatise Roadmap by the
Department of Agriculture seeks to bring Ireland to a climate-neutral status by 2050. Although this
deadline is far into the future, Minister of State in the Department of Agriculture, Food and the
Marine, Senator Pippa Hackett said: “Greenhouse gas and ammonia emissions from the sector have
been going in the wrong direction. We need a clear pathway to reverse this trend, and this roadmap
sets us on that path.’’

The new scientific papers emerging from Teagasc research show that getting soil pH
right, through liming, can significantly reduce emissions of nitrous oxide, a potent greenhouse gas.

The results from the study show that applying five tonnes of lime per hectare every three to four
years, has the potential to increase soil pH from 5.1 to 6.9, reducing the nitrous oxide emissions by 39%. Farmers can simultaneously improve soil pH for agronomic benefits while also reducing N2O emissions, ultimately a win-win for both the farmer and the environment. Senior Research Officer at Johnstown Castle, Dr David Wall stated that: “using an existing long-term intensive grassland liming and phosphorus trial, this research investigated the effect of longer-term lime and phosphorus management and their interaction on N2O emissions and grassland productivity”.

Long term liming works to increase returns of organic matter to the soil whilst allowing for a linear decrease in nitrous oxide emissions with the increase in soil pH from application

All the while, applying lime to soils of an acidic pH, less than 6.5, looks to increase soil biological
activity, while raising soil respiration rates and organic matter mineralization, sequentially resulting
in increases in plant productivity. From the study, long term liming works to increase returns of
organic matter to the soil whilst exhibiting a linear decrease in nitrous oxide emissions with the
increase in soil pH from the application. In an intensive grassland plot located in a humid, temperate
climate, the study found that a soil limed to a pH of 6.9 emitted 36% less nitrous oxide per ton of DM
yield under the same management and fertiliser regime compared to the same soil with a pH of 5.1.
It was observed that the year prior to liming and phosphorus application, reseeding of the grassland
showed a very positive effect on sward establishment and yield. The study shows by adjusting the
soil pH above the agronomic optimum of 7 for most crops, in combination with optimal phosphorus supply, the most favourable outcome from the study in terms of both environmental and agronomic
benefit can be obtained. This is again another finding that is not only good for the environment but
is also of benefit to the farmer. Through the application of good farming and grassland practices, the
outcome can result in a considerable nitrous oxide mitigation potential in temperate grasslands.

While livestock numbers are still the main driver of agricultural greenhouse gas emissions with
approximately 80% of emissions associated directly to the animal, fertiliser nitrogen accounts for
12%, with soils and carbon dioxide from lime manufacturing making up the remainder. Under the
government's Ag Climatise 2050 roadmap, a reduction of nitrous oxide emissions by 40-50% is
sought. This new research by Teagasc would point towards a brighter future for policymakers,
whereby their overall goals can not only be backed by scientific knowledge but put into practice by
producers whose production targets will align with policy.

The research findings are undoubtedly indications of a step in the right direction for sustainable
farming in Irish agriculture. Farmers and advisors should not only take the initiative to follow this
new research but to encourage and educate those that may not have access to the scientific writings. Sustainability is not only on producers’ minds but also policymakers, whereby in the coming years' new research and findings such as these may be drawn into legislation. It is within every farmer's interest to get ahead of the game and start putting this research into practice.