Teagasc is advising tillage farmers that achieving carbon neutrality within their businesses should be a feasible objective within a reasonable period of time.
However, the challenge facing livestock farmers in this regard will be much greater.
These were two of the main conclusions emanating from Teagasc’s second national crops’ forum, which was held recently.
Lower carbon footprint for tillage farmers
Johnstown Castle-based Dr. Gary Lanigan explained: “Cereals have a much lower carbon footprint than either beef or milk.
“The respective figures are: 0.3 to 0.5kg of CO2 per kg of grain; 1.0kg of CO2 per kg of milk and 16.0kg of CO2 per kg of meat.”
According to Lanigan, emission levels of nitrous oxide from tillage soils are lower, relative to the levels expected from grassland sites which, invariably, contain higher levels of organic carbon.
He added:
“However, nitrate leaching rates are highest from tillage soils.”
Specifically, where carbon is concerned, Laningan confirmed that a typical grain crop will assimilate 12.0t/ha of carbon courtesy of photosynthesis.
However, carbon losses from crops are significant. Respiration will account for the equivalent of 5.0t/ha; the removal of the grain at harvest will account for an additional 4.0t, with straw removal accountable for 2.0t/ha.
“Approximately 1t/ha of carbon is stored in the crop’s root system. However, subsequent decomposition will reduce the amount of carbon actually incorporated into the soil to around 0.2t/ha,” said Lanigan.
Soil type
The Teagasc advisor indicated that soil type determines the amount of organic carbon that it contains.
Brown earths tend to contain the lowest levels of carbon with peaty soils ranking highest in this regard.
Lanigan continued:
“Adding farmyard manure and chemical fertiliser will increase soil organic matter levels within any cropping system.
“The use of min till cultivation systems, as opposed to ploughing, helps to maintain soil carbon reserves, but only at the very top levels of the soil profile.”
Straw incorporation for tillage farmers
Research has confirmed that straw incorporation will act to increase soil organic carbon levels.
It has been estimated that between 10% and 20% of straw carbon remains in the soil.
Over a period of 20 years, it has been shown that incorporating 4.0t of straw/ha per annum will increase soil carbon levels by 8%. This manifests itself in the amount of microbial biomass found in soils.
Lanigan commented: “The growing of cover crops will also act to boost soil organic carbon levels. Over a 20-year period between carbon incorporation, rates of between 10t/ha and 15t/ha can be expected.
“Highly managed hedgerows can absorb up to 0.2t of CO2 per km, per annum. This figure rises if the hedgerows are allowed to grow taller and wider.
“Broadleaf woodland can absorb approximately 19t of atmospheric CO2/ha per annum.
Organic carbon
“Soil organic carbon is important when it comes to increasing crop yields and soil quality,” Lanigan added.
“Rotations, cover crops and grass leys are effective at increasing soil carbon levels within a tillage system.
“Woodland and hedgerow management can help to achieve a carbon neutral tillage farm,” he concluded.