Tillage a small player in emissions reduction…but still work can be done

It’s a well-known figure, 32% – the contribution of agriculture to national greenhouse gas (GHG) emissions. The sector had been going in the right direction in reducing these emissions, but not anymore.

Karl Richards, speaking at last week’s Teagasc National Tillage Conference, gave some facts, figures and possible actions to reduce the amount of gases being emitted to the atmosphere.

“From the early 2000s onward we saw about an 18% reduction in GHG emissions and then, we can see, with the abolition of milk quota those emissions have gone back up,” Karl stated.

“Agriculture is still not emitting as much carbon as it was back in the late 1990s, but this is a major problem.

In an era of reducing emissions we’re going in the wrong direction.

Karl explained that two-thirds of these emissions come from methane and one-third come from nitrous oxide. Methane comes from livestock, while nitrous oxide is associated with fertiliser and manure use.

Data source: Teagasc

He noted that nitrogen (N) use efficiency is the main area where tillage farmers can reduce emissions. Karl commented that a lot of tillage farmers also have livestock and those animals are probably the main source of carbon emissions on their farms – this was found to be the case in the National Farm Survey of 2017.

Karl explained that to offset emissions by 10% there are a number of steps which can be taken. The majority of these measures are associated with livestock as can be seen in the graph below.

N use efficiency, he explained, is really the only measure relating to tillage.

Carbon sequestration

Karl added that carbon sequestration also has to be improved by 10% and he showed ways which this can be achieved. He explained that forestry is the biggest offsetting.

Most of this forestry is forestry that is already planted. This is forestry that’s already in the ground and accounts for the lion’s share or carbon sequestration.

Forestry accounts for 2.1MT (megatonnes) of carbon dioxide. He added that water table management of organic soils, in other words the re-wetting of bogs to the tune of 40,000ha, would offset nearly half a megatonne of carbon.

“If the country re-wetted 40,000ha, it would offset nearly half a megatonne of carbon, which is a massive amount of carbon and it will do that every year for millennia.”

Pasture management could account for 0.26MT, while tillage measures of growing cover crops and straw incorporation would account for 0.16MT.

“We need to apply lots of different small little actions to generate the savings and increase carbon sequestration in the soils,” Karl noted.

How can tillage farmers improve their carbon footprint?

“Tillage farming is very ambitious already in terms of GHG emissions, but there are ways that we can further reduce emissions. First of all, [this can be done] by optimising our soil fertility – pH, P [phosphorus] and K [potassium] in our soil.”

Karl noted that healthy soils require less fertiliser and this in turn improves our nutrient use efficiency. He added that unless farmers are getting more yield then more N should not be applied.

Excessive N applications can lead to the emission of nitrous oxide gas, which accounts for 33% of our GHG emissions. Applying N at the wrong time can also result in more of these emissions.

Karl noted that using animal manures is a good step in improving soil health and nutrient use efficiency.

“Animals were brought onto farms in the past for a reason – to use non-human edible products and to produce manure to return to the soil.”

The researcher, who is based at Johnstown Castle, noted that returning straw to the soil can also increase soil organic carbon levels.

Image source: Teagasc

Cover cropping over winter can also increase soil organic carbon and soak up nutrients over winter. In both cases he noted costs associated with these steps.

He also added that including grass in rotations will increase soil carbon levels, but ploughing these soils can release carbon.