Worming our way towards healthier soils
New research involving UCD has quantified the effects of farming practices on earthworm populations in soils. Associate Professor Olaf Schmidt spoke to Claire O’Connell.
Earthworms. Whether they fascinate or repel you, collectively we humans owe them a huge debt of gratitude. As ‘nature’s plough’, worms churn and enrich the soil, enabling it to support life and grow the food we ultimately eat.
But are we doing worms a disservice with intensive tillage practices that mechanically break up the soil?
A new analysis involving UCD shows that keeping soil disruption to a minimum and covering soils with harvest residue or manure is the formula to keep those worms alive and working.
“In farming systems earthworms are the goody-goodies, they are highly beneficial, everything they do is good for us,” says Associate Professor Schmidt, UCD School of Agriculture and Food Science.
Worms are ‘ecosystem engineers’, explains Associate Professor Olaf Schmidt, describing how their mechanical movements and digestion in the soil can shape the environment.
“They work the soil,” he says. “They eat a lot of soil, they decompose harvest residues and manure and they excrete water-stable soil aggregates, which is good for soil structure and productivity. They release nutrients so plants and other organisms can use them and they make physical channels or tunnels in the soil, which are highways through soil for water and air.”
Also, perhaps less fun for the earthworm, they themselves are a source of food for other animals such as birds and badgers. “This is important for biodiversity,” says Associate Professor Schmidt.
So we are agreed: earthworms are good to have around. But what happens to worm populations when tillage practices in farming, such as conventional ploughing, mechanically disturb the soil?
To take a global look, Associate Professor Schmidt and Professor María J. I. Briones from the Universidad de Vigo analysed data from 276 studies across 40 countries dating as far back as 1950.
“There are a lot of individual studies in various countries and soil types and using different methods, and we ourselves have done some of those studies,” says Associate Professor Schmidt.
“We wanted to get a global, quantitative picture, so we extracted the main results from all those studies and applied statistical analysis to mine into the data and tease out the generalisable effects of farming practices on worms.”
The meta-analysis, published in the journal Global Change Biology, found that intensive tillage practices reduced the earthworm population of soils, while a more ‘conservation’- led approach of reduced tillage and covering the soil with harvest residue, manure or mulch seemed to offer an environment where worms could thrive.
The gritty details
Compared to conventionally ploughed soils, untilled soils had an average of 137% more worms and 196% more biomass, while the conservation approach saw an average of 127% more worms and 101% more biomass. “With this study we have been able to quantify the effects on worms of various tillage practices around the world, in different soils and climatic conditions,” says Associate Professor Schmidt.
By digging into the data, the researchers were also able to identify that larger species of worms were more sensitive to the detrimental effects of intensive tillage.
“There isn’t just one type of earthworm, in Ireland alone we know of 28 species,” says the UCD researcher. “So we looked at the effects of farming practices on the 13 most common species and we found the positive effect of reduced tillage is largest for species which we call the anecics. These are large worms that live all their lives in a single vertical channel called a macropore in the soil, which can take in water. If you plough the soil, these worms are chopped and killed and the channels are destroyed.”
Soil is a living entity, it is really complex and it has been described as a thin veneer that sustains us all. But it is not renewable in our lifetime, so we have to protect it.
Feed worms, don’t turn them
When the study was published, Associate Professor Schmidt was inundated with interest from farmers and others who work with the soil. “Farmers are interested in soils, they know their livelihoods depend on them,” he says. “And worms are a visible indicator of how the soil is doing. If you dig up a bit of the soil and see lots of different kinds of worms that’s good. If not, the farmer knows there is a soil issue.” Associate Professor Schmidt’s advice to farmers is to consider adopting reduced tillage practices. “The worms will do many of the functions of the plough, they will mix the soil and incorporate manure,” he says. “And if you help the earthworms you help to improve the soil quality overall.”
Soil – the thin veneer that sustains us Associate Professor Olaf Schmidt is unequivocal when it comes to stressing the importance of soil for humans and for the planet. “The existence of humankind depends on soil,” he says. “We get almost all of our food from soil, it locks up carbon and purifies water and provides a habitat for biodiversity.” He became fascinated with the biology of soil as a student in East Germany, and became ‘hooked’ on teasing out the many secrets science is discovering about it. “Soil is a living entity, it is really complex and it has been described as a thin veneer that sustains us all. But it is not renewable in our lifetime, so we have to protect it,” he says. “UCD has a really good history in soil ecology and although the field work can be hard – you sit in a wet field and sort soil for ages – it is also great fun.
Associate Professor Olaf Schmidt was in conversation with Claire O’Connell, science writer and contributor to The Irish Times and Silicon Republic
This article first appeared in the Spring 2017 edition of UCD Today