Professor John Quinton reflects on the importance of the humble soil beneath our feet, following the annual meeting of the British Society of Soil Science hosted at Lancaster Environment Centre.
No soil – no life
The Earth was a very different place 417 million year ago. Carbon dioxide concentrations in the atmosphere were much higher, and the first plants were only just starting to emerge. This was a critical time in the history of the Earth, not just because of the evolution of plants, but also because it was when the first soils started to form.
“Soil? How can the formation of soils be as important as the evolution of plants?”. I hear you ask. The presentations at the annual meeting of The British Society of Soil Science, held recently at Lancaster Environment Centre, told us why.
Joe Quirk, from Sheffield University, described his experiments showing the important role played by mycorrhizal funghi in chemically altering rocks and reducing the carbon dioxide concentrations in the atmosphere 400 million years ago.
This early rock and soil mineral alteration (weathering) would have been partially responsible for reducing carbon dioxide concentrations in the atmosphere and so allowing the development of life on earth. However, those early plants and fungi had to have their roots in something, and that something was soil. Those early soils would not only have supported the plants by providing them with somewhere to put their roots, but will also have begun to store carbon much like the soils of today.
Today’s soils store vast amounts of carbon. It is estimated that the organic soils of Britain store as much carbon as is emitted by the entire world’s industry in one year. So it is not surprising that many researchers are looking for ways of increasing the soils ability to store carbon. However changing the carbon content of a soil is more easily said than done.
Adding organic manure to the soil seems like a good plan, however, the soil responds very slowly to the conditions of organic matter and long term experiments, such as in the Calhoun Experimental Forest described in Dan Richter’s Keynote talk, show us that it takes many years for soil carbon contents to change. This is the thing about soils, they change slowly and take a long time to build.
How long have we got?
Dan Richter described soils which were 4 million years old. These soils are not just the product of one environment, but have been ‘formed’ and ‘reformed’ many times in response to changes in the environment. He also pointed out that soils are no longer “natural” but are heavily modified by human activities.
There are perhaps few places on earth where soils are as modified as in the British Isles. Andrew Tye, from the British Geological Survey, presented a timeline of soil use in the English Midlands dating back to Roman times. It showed a repeated cycle where the soils were cleared for agriculture, abandoned after the soil became exhausted, returned to Forest and then cleared again.
If Andrew’s timeline is correct then this Midland soil sustains agriculture for around 400 years in each cycle. Currently it’s back in agriculture again but this time with a critical difference, the availability of inorganic nitrogen and phosphorus fertilisers. Will these additions be enough to sustain these soils far into the future?
It is hard to predict the answer to this question. Models such as those described by Lancaster University’s Jessica Davies, which might help by predicting soil change over tens or hundreds of years, are only just being developed. As Dan Richter pointed out, getting this long-term perspective is hard: it not only requires models but a long term commitment to monitoring soil change and establishing experiments which can study changes resulting from management interventions. The understanding that we can glean from these experiments can only help us to improve our predictions of future.
Although our models are currently uncertain, one thing is certain, without soils the Earth returns to an inhospitable planet similar to the one we had 470 million years ago. Learning how to care for our soils so that they still function long into the future requires us to act now.
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