Topsoil needs a little more consideration

Scientists have provided what they say is the first worldwide snapshot of how soil erosion may be affecting the longevity of our soils.

A team from the UK, China and Belgium analysed data collected at 255 locations across 38 countries on six continents to calculate soil lifespan – how long it would take for the top 30 centimetres of soil to erode at each location.

The study included soils that are conventionally farmed and others that are managed using soil conservation techniques.

It found more than 90% of the former were thinning, with 16% having lifespans of less than a century. And these were found all over the world, from Australia, to Asia, to the Americas.

“There have been many headlines in recent years suggesting that the world’s topsoil could be gone in 60 years, but these claims have not been supported with evidence,” says Dan Evans of Lancaster University, lead author of a paper in the journal Environmental Research Letters.

“This study provides the first evidence-backed, globally relevant estimates of soil lifespans.”

There are, however, some causes for optimism, Evans and his colleagues note.

Soils managed with conservation strategies tended to have longer lifespans, and in some cases these practices promoted soil thickening. Only 7% of soil under conservation management had lifespans shorter than a century, and nearly half exceeded 5000 years.

Converting arable land to forest was found to be the best way to lengthen soil lifespans. However, other approaches that allow farming to continue, such as cover cropping, where plants are grown between cropping seasons to protect the soil, were also shown to be highly effective.

The ploughing of land along contours rather than downslope, and hillslope terracing were similarly suggested as beneficial for lengthening soil lifespans.

“It is clear that we have a conservation toolbox that can slow erosion and even grow soil. Action is needed to promote the adoption of these measures…,” says Lancaster’s John Quinton, a co-author.

The researchers say their analysis reveals a wide distribution of soil lifespans, encompassing five orders of magnitude and “partly reflective of an extensive variation in the underlying driving variables such as climate, slope and soil texture, which in turn can influence the efficacy of soil management techniques”.

“However, soils with human-scale lifespans shorter than 100 years are present in all of the observed regions, including many of the world’s wealthiest nations. This clearly demonstrates that soil erosion is one of the most critical threats to soil sustainability globally…,” they write.

The research was a collaboration with China’s Chang’an University and KU Leuven in Belgium.