Earth has lost a third of arable land in past 40 years, scientists say

Another example of something we have known about for years, and have chosen not to correct.

I am being required to rake up the leaves in my yard, which is a stupid waste of time. When I owned my own house, I left the leaves in the yard, and by spring they had mostly decomposed, returning nutrients to the soil and adding organic matter that improved the clay soil. After decades of people being required to rake up their leaves in the fall, the place where I live now has eroded soils with little humus in it.

I do have a compost heap, but most people back up the leaves, & they are collected and disposed of.

Notice that in forests of hardwood trees, where the leaves are left where they fall, they don't collect to great heights.

http://www.theguardian.com/environment/2015/dec/02/arable-land-soil-food-security-shortage

Oliver Milman
Dec. 2, 2015

The world has lost a third of its arable land due to erosion or pollution in the past 40 years, with potentially disastrous consequences as global demand for food soars, scientists have warned.

New research has calculated that nearly 33% of the world’s adequate or high-quality food-producing land has been lost at a rate that far outstrips the pace of natural processes to replace diminished soil.

The University of Sheffield’s Grantham Centre for Sustainable Futures, which undertook the study by analysing various pieces of research published over the past decade, said the loss was “catastrophic” and the trend close to being irretrievable without major changes to agricultural practices.

The continual ploughing of fields, combined with heavy use of fertilizers, has degraded soils across the world, the research found, with erosion occurring at a pace of up to 100 times greater than the rate of soil formation. It takes around 500 years for just 2.5cm of topsoil to be created amid unimpeded ecological changes.

“You think of the dust bowl of the 1930s in North America and then you realise we are moving towards that situation if we don’t do something,” said Duncan Cameron, professor of plant and soil biology at the University of Sheffield.

“We are increasing the rate of loss and we are reducing soils to their bare mineral components,” he said. “We are creating soils that aren’t fit for anything except for holding a plant up. The soils are silting up river systems – if you look at the huge brown stain in the ocean where the Amazon deposits soil, you realise how much we are accelerating that process.

“We aren’t quite at the tipping point yet, but we need to do something about it. We are up against it if we are to reverse this decline.”

The erosion of soil has largely occurred due to the loss of structure by continual disturbance for crop planting and harvesting. If soil is repeatedly turned over, it is exposed to oxygen and its carbon is released into the atmosphere, causing it to fail to bind as effectively. This loss of integrity impacts soil’s ability to store water, which neutralizes its role as a buffer to floods and a fruitful base for plants.

Degraded soils are also vulnerable to being washed away by weather events fueled by global warming. Deforestation, which removes trees that help knit landscapes together, is also detrimental to soil health.

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The academics behind the University of Sheffield study propose a number of remedies to soil loss, including recycling nutrients from sewerage, using biotechnology to wean plants off their dependence upon fertilizers, and rotating crops with livestock areas to relieve pressure on arable land.

Around 30% of the world’s ice-free surfaces are used to keep chicken, cattle, pigs and other livestock, rather than to grow crops.

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tags: human impact on environment