Cropping

How much soil goes ‘down the drain’ each year?

European Commission Joint Research Centre, December 18, 2017

ALMOST 36 billion tonnes of soil are lost every year due to water, and deforestation and other changes in land use make the problem worse, according to a new study by the University of Basel, the European Commission – Joint Research Centre and the Centre for Ecology & Hydrology (CEH, UK).

The study also offers ideas on how agriculture can change to become a part of the solution from being part of the problem.

Soil is an essential resource for satisfying human needs, such as food and feed production, fibre, clean air and water. Soil is not an infinite resource though. Human activity and changes in land use lead to increased soil loss, which in turn degrades nature’s recycling system and diminishes land productivity, thus decreasing human wellbeing worldwide.

The research findings, “An assessment of the global impact of 21st century land use change on soil erosion”, offer an unprecedentedly thorough, high resolution assessment of global soil loss.

The spatial pattern of soil erosion in 2012. Areas classified as having very low, and low erosion rates represent almost 85 percent of the study area. About 7.5 million km2 in total (6.1 percent of the land), exceeds the generic tolerable soil erosion threshold. (Photo: European Union, University of Basel)

 

The study quantifies the effects of land use change between 2001 and 2012 and finds that during this period, 35.9 billion tonnes of soil had been displaced due to water (mostly rainfall) annually.

This is the equivalent of the weight of the concrete that it would take to build 250 of the world’s largest dam, the Three Gorges Dam in China.

Soil loss increased by 2.5 per cent between 2000 and 2012 mainly due to clearing down forests for agricultural purposes.

Soil erosion hotspots

Soil erosion doesn’t strike evenly. Moderate to high soil erosion impacts about 9.3pc of Earth’s land surface, and it exceeds the generic tolerable soil erosion threshold for 6.1pc of the land surface, or about 7.5 million square kilometres.

The greatest increase in soil loss is estimated for Sub-Saharan Africa, South America and Southeast Asia. This means that countries with less developed economies are estimated to have experienced the highest soil erosion rates.

South America surpasses Africa with an estimated increase of soil erosion of over 10pc in 2012.

This seems to be driven mostly by deforestation and the large expansion of cropland areas in Argentina (41.6pc of its territory dedicated to cropland), Brazil (19.8pc), Bolivia (37.8pc) and Peru (5.9pc). During the same period, soil erosion in Africa increased by 8pc, mostly in the Equatorial countries.

The largest and most intensively eroded regions are in China (0.47 million km2, 6.3pc of the country’s land area), Brazil (0.32 million km2 or 4.6pc the country’s land area) and African Equatorial territories (0.26 million km2, 3.2pc of the region).

Conservation agriculture saves soil

Soil erosion can be reduced if soil conservation practices are adopted in agriculture.

The study estimates that, if applied correctly, conservation practices could save over a billion tonnes of soil per year.

Conservation agriculture currently covers about 15.3pc of the observed cropland globally, reducing soil erosion by an estimated 7pc.

The highest reductions in soil loss due to conservation agriculture are estimated in South America (16pc), Oceania (15.4pc) and North America (12.5pc).

Unique methodology

The study investigates global soil erosion dynamics by means of high-resolution spatially distributed modelling (ca. 250?×?250?m cell size).

The geo-statistical approach allows, for the first time, the thorough incorporation into a global soil erosion model of land use and changes in land use, the extent, types, spatial distribution of global croplands and the effects of different regional cropping systems.

This, coupled with an improved global assessment of rainfall erosivity dynamics and the latest globally consistent dataset resulted in a state-of-the-art global model based on the Revised Universal Soil Loss Equation or RUSLE.

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The study was produced by a group of researchers, led by the University of Basel, the European Commission – Joint Research Centre and the Centre for Ecology & Hydrology (CEH, UK).

https://www.eurekalert.org/pub_releases/2017-12/ecjr-hms121517.php

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