Instead of throwing piles of chemical fertilisers on our fields, there is a new alternative. By Bernard Carey
Climate change is now generally an accepted fact by most people. There is still some debate as to whether it is man-made or just part of the earth’s natural cycles. But the facts speak for themselves; it is not possible to keep releasing greenhouse gases such as carbon dioxide, methane and nitrous oxide without seriously negative outcomes.
In addition soils are being eroded by overuse. Fortunately, to date, we have been able to replace soil nutrients via artificial inputs from the chemical industry. However, whilst nitrogen and potassium may not be about to run out in the future, the same cannot be said about phosphorus. It is estimated that supplies of this nutrient could run out within 75 to 200 years. Phosphorus is a finite resource, so we will have to learn to manage our soils differently into the future.
The science of “biochar” could prove to be the next step in better soil management. Biochar is ground-up charcoal, inserted into the soil to improve its quality.
Charcoal has traditionally has been made from cutting down trees. Many people might be shocked at the thought felling a forest to make biochar. But actually modern biochar doesn’t need trees at all. Biochar can be made from any biomass, for example wood, grass, sewage sludge, farmyard manure, mushroom compost or rushes. It is made by heating the biomass in a low oxygen environment at high temperatures (around 500oC) in a specially-designed kiln. What is left is charcoal. If it is ground up and added to the soil, it is called biochar.
So imagine a farmer who has a problem with rushes: he could potentially harvest them (here’s hoping for more dry summers); use this biomass to heat his house; then use the residue, biochar, to give a better quality silage and also add it to the slurry pit; thus reducing green-house gas emissions and in turn producing a better quality slurry for his land.
So why use Biochar? The answer lies in the form of carbon that makes up the biochar. Fungi and bacteria cannot break this down. This makes it valuable to bacteria, fungi and protozoa. As these microorganisms are microscopic, they can shelter and multiply in the numerous tiny pores in the carbon. And we need such soil microorganisms in our soils – they help plants get the nutrients they need to thrive. Biochar enables the soil to hold on to essential nutrients for plants. Biochar is also very porous, and hold onto water in droughts, and prevent nutrients washing away during heavy rain. It does all the things a good compost does (except fertilise), but unlike a good compost it improves with age in the soil and does not disappear.
Some farmers add bags of rich compost to their soil and when they repeat the process a year later there are no signs of last year’s compost – bacteria and fungi broke it all down. By adding biochar you get similar results only it remains in the soil.
The term biochar may be new, but its use is not; in fact the use of charcoal in Irish soils goes back to the 17th and 18th century. This material was introduced either directly as an off-shoot of the extensive charcoal industry that once was in Ireland, or indirectly through a technique call ‘paring and burning’ whereby the sod was pared off the land and left to dry and then heaped and burnt. This material was then spread on the land and gave excellent results. Unfortunately such a system was unsustainable and over time the soil was depleted.
Today the proposal is to use ‘clean waste biomass’ to generate heat and power and then land-spread the leftover biochar. Such clean waste biomass could come from straw, furze, scrub, miscanthus, willow, chicken litter, corn chaff or even rushes.
Biochar also can reduce greenhouse gas emissions in soils. By adding it to the slurry pit you get better nutrient retention and consequently fewer emissions when spreading slurry on land. Also, it can be added to silage to produce a better end product, added to livestock feed to improve digestion, and added to livestock cubicles to reduce odours.
The production of biochar doesn’t really work on a large scale, despite big business being interested in doing so. What could work better is operation on a smaller scale – mobile plants that can be towed behind a 4WD vehicle, or larger units installed on farms to meet local needs.
More research and field trials are required as there are many variables affecting the use of biochar in soil. But unlike other parts of the world where they have vast amounts of waste material that can be transformed into biochar such as rice husk, or the residue from cane plantations, or moth-damaged trees in North America, Ireland does not have an excess of such material. The future of biochar in Ireland lies in its integration into existing agricultural activity. Using biochar, Irish farmers can reduce the cost of soil additives, and they can maximise the waste from agriculture. This is a win-win situation for the farmer and the environment.
Maybe in the future it will be possible to have a degree course in biochar given it encompasses all the sciences: physics, chemistry, and biology; in addition to economics, social science and historical engineering.
For more information on biochar, see here.