As Siobhan Walsh reported this week, the carbon footprint of Irish tillage farms is low. On average, Irish tillage farms produce 0.1kg CO2e/kg of grain.
This is considerably lower when compared to other sectors, such as dairy (1kg CO2e/kg of milk) and beef (16-20kg CO2e/kg of meat).
Despite its very positive emissions profile, tillage, like all other sectors in agriculture, will be asked to do more.
Luckily for the tillage sector however, the measures necessary to reduce emissions even further than this stand to benefit tillage farmers.
Increasing soil organic carbon (SOC) levels in tillage soils will play a key role in achieving this. Tillage soils tend to have the lowest levels of soil carbon.
According to Teagasc’s Gary Lanigan, this is partly due to the use of ploughs, which break up soil aggregates and expose the organic carbon in the soil to microbes.
Microbes, in turn, use this organic carbon as an energy source, resulting in the respiration of CO2.
However, soil type, specifically its clay content, also has a considerable bearing on the carbon sequestration capacity of the land.
Sandy soils, for example, have poor sequestration capacity, while peat soils, as we know, have enormous capacity.
What can you do to increase soil carbon levels?
Increasing SOC levels doesn’t just help the climate, it improves soil cation exchange capacity, which increases soil’s nutrient availability, soil water holding capacity and overall soil fertility.
Furthermore, healthier soils tend to support bigger crops, which increases root and crop residue carbon input into soil. The following measures can increase soil organic carbon levels.
One of the first things you can do is to add manure onto the soil. Adding farmyard manure (FYM) or slurry over consecutive years allows you to get a large build-up of soil organic carbon. Around 25% of applied manure carbon in a given year is retained. The amount of SOC added to the soil depends on the rate at which it is applied and of course, the type of manure applied – see Table 1.
The Straw Incorporation Measure has proven popular with the tillage industry and many farmers hope it is here to stay. About 10%-20% of the carbon returned from chopping straw is estimated to remain in the soil.
By chopping 4t of straw per hectare each year for 20 years, this will increase SOC by 8%, according to Gary. It can also result in a 40% increase in microbial biomass, even under low levels of incorporation.
Cover crops play a big role in increasing SOC levels, but over a long period of time. Gary explained that SOC can increase by 12-15t/ha by growing cover crops over a 20-40 year period.
Cover crops help reduce the fallow season, which in turn lowers the carbon loss from soil.
Minimum tillage is good for soil structure and soil health. However, in terms of SOC levels, while you get much higher levels in the top 10cm of soil, there is very little difference between a minimum tillage system and a plough-based system as you move down the profile.
Hedgerows and woodland
Finally, tillage farmers need to look at how they manage hedgerows. To many readers, a well maintained and trimmed hedgerow is a sign of good management.
However, Gary said this isn’t the case. A typical hedgerow can sequester 0.2t of CO2/km per year.
If you allow your hedge to grow out a meter and up a couple of meters, its sequestration potential increases significantly, to between 2-4t CO2/km per year.
Planting trees such as broadleaved woodlands could sequester a further 19t CO2/ha per year, or 30t CO2/ha in the case of a sitka spruce plantation.