Boost soil carbon levels for healthier medium and yields

Agriland

26-04-2025

It is often remarked that Irish soils have been badly damaged over the years through ill husbandry and exploitation of its inherent nutrients and structure.
These are weighty charges that are not to be dismissed lightly, for it is upon soil that all farming – and ultimately human nutrition – is based, so its proper functioning is important to all of us.
Yet before we can ask after the state of a soil, we need to get to grips with what it actually is for. Although there is soil everywhere we go, familiarity tends to blunt our interest in the finer details of its composition and purpose.
Thin layer of life
A simple description is that soil is the boundary layer between the rock of this planet's outer shell and the atmosphere, where that rock lies above the level of the oceans.
Soil is composed of three main constituents – minerals, water, and gasses – with the organic matter sometimes being divided into dead carbon-based material and live organisms.
Optimum soil will contain 25% water and 25% air, according to Lena Madden, senior research fellow at the Technological University of the Shannon (TUS).
While this is the ideal, she questions the existence of such a soil in Ireland, pointing out that we have a wet climate which tends to encourage the waterlogging of soil, excluding the air that is so vital to its health.
Moisture management
There is little can be done about the climate, so controlling the rainfall is out of the question.
Yet the rate at which the water drains away or is retained are factors that can be modified to large extent, so it is these that farmers need to focus on when optimising soil husbandry.
Soil acidity and nutrient status are the two main features over which there is a great deal more control, and it is these that the Irish government have focussed on through the advice given by Teagasc over the years.
Dr Lena Madden (fourth from left) with colleagues from the Irish Living Labs project
However, Dr. Madden questions whether these are still the appropriate factors to highlight when considering the health of the soil, for soil needs to function as a growing medium, rather than just a reservoir for nutrients, if yields are to be maintained.
To function properly, soil needs a structure, which is often badly damaged by compaction.
Dr, Madden highlights this compaction as a major concern, suggesting that perhaps it would be better to address this issue instead of the pursuit of ensuring a supposedly correct balance in the nutrient bank.
The senior research fellow also urges for soil not to be regarded as a lifeless mix. She said it is the microorganisms within it that create the structure, and it is the care for these -be they worms, fungi, or any of the millions of species that live beneath the ground – that holds the key to soil health.
Dr. Madden also suggested that we must also stop regarding the the first 5-10cm of soil as its true extent.
She said he roots of a pasture should extend to 20-30cm and stock farmers need to consider the functioning of the soil at this depth alongside the mat of roots nearer the surface.
Carbon is the answer
Compaction is the curse of all soils and, here in Ireland, the high rainfall exacerbates the issue, not only discouraging root growth but causing run-off and the erosion of soils.
The best way to improve the situation, Dr. Madden believes, is to increase the amount of organic carbon in soils, and she has set this out as a major focus for the studies and trials being conducted under the EU-funded Living Lab project.
Meanwhile, the researcher urges farmers to do whatever they can to add more carbon to their soils, noting that one quick fix may be the addition of woodchips mixed with slurry, though she notes that all solutions are site-specific.
Two factions, two resources
As for slurry itself, the ability to separate it and treat the two factions as different materials is a step forward and may hold potential in helping to extract the greatest benefit from it.
Using either slurry or crops for energy production is a waste of resources according to Dr Madden
Bovine-sourced farm slurry is a great carbon resource, although it will vary in nutrient content, and Dr Madden has no time for feeding it to an anaerobic digester for the production of methane.
This, she points out, removes a large part of the carbon from the material, as is intended, leaving a nutrient-rich broth thatoffers little benefit in the way of improving soil composition and structure.
Compost for soil
Composting of carbon-rich residues, such as straw and other crop residues, in conjunction with slurry is another idea that appeals to those wishing to address the deficit of organic carbon in soils.
Compositing dairy bedding in a purpose-built facility in the Netherlands. The farm specialises in high-value crops
Unfortunately this is a process which adds costs to production in the short-term. While the benefits should appear further down the line as soil condition improves, that is a hard sell to many in conventional farming.
Crop residues such as forest thinnings are also in demand from power stations running on biomass, further adding to the competition between farmers and the energy industry for what were once considered waste products.
Overall outlook
There has always been an appreciation of the role of organic matter in farming.
With the post-green revolution. much of this understanding was swept away with the reliance on scientific method rather than the wisdom and empathy developed over hundreds of generations.
It is that course of action which is being questioned now as never before, as overall yields plateau rather than enjoy the dramatic annual increases experienced during the years leading up to the turn of the century.
In an effort to once more push forward with increasing yields, or maintaining yields whilst reducing inputs, the Living Labs project is seeking to reintroduce the accumulation and dissemination of knowledge horizontally between farmers at ground-level, and displacing to a certain extent the current top-down approach of institutions instructing and advising.
It is this approach which Dr Madden feels will help reinforce the circularity of farming and, by extension, society in general through a collective approach that holds a healthy rural community at the heart of its efforts to feed humanity.