Scientists are already worried about the rapidly growing human population, which is approaching unsustainable levels and threatening global food security. And now, new research shows that soil losses may exacerbate this problem and result in possible ramifications for human security.

In the journal Science, a group of leading soil scientists outline threats to soil productivity - and, in turn, food production - due to soil erosion, nutrient exhaustion, urbanization and climate change.

"Soil is our planet's epidermis," Donald L. Sparks, from the University of Delaware, said in a statement. "It's only about a meter thick, on average, but it plays an absolutely crucial life-support role that we often take for granted."

"Historically, humans have been disturbing the soil since the advent of agriculture approximately 10,000 years ago," he continued. "We have now reached the point where about 40 percent of Earth's terrestrial surface is used for agricultural purposes. Another large and rapidly expanding portion is urbanized. We're already using the most productive land, and the remainder is likely to be much less useful in feeding our growing population."

The planet is predicted to house approximately 11 billion people by the year 2100. The key to producing enough food will be to find better ways to manage the agricultural lands we already have, according to Sparks, rather than expanding into new areas. However, this is no trivial task.

And already the Earth is experiencing problems that make achieving this feat difficult. Soil erosion greatly exceeds the rate of soil production in many agricultural areas. For example, in the central United States - long considered to be the "bread basket" of the nation - soil is currently eroding at a rate at least 10 times greater than the natural background rate of soil production.

The loss of soil to erosion also involves a reduction in key nutrients for plant growth, leading to the need for commercial fertilizers. However, the current rate of fertilizer production is unsustainable, researchers say.

"The evidence for this is in the recent spike in the price of fertilizers," Sparks explained. "The primary components of fertilizer are either very energy-intensive to produce or they are mined from limited supplies on Earth. It's a classic supply-and-demand situation leading to large price increases that must eventually be passed on in the price of food."

And prices are not likely to go down any time soon. According to the study, the largest reservoir of rock phosphate in the United States is expected to be depleted within just 20 years. When that happens, society will need to begin importing this source of the essential nutrient phosphorus.

"Unless we devise better ways to protect and recycle our soil nutrients and make sure that they are used by crops efficiently rather than being washed away, we are certainly headed for nutrient shortages," Sparks concluded.

Not to mention competition for valuable and scarce food resources could result in more than world hunger - it could also cause geopolitical conflict.

"Human civilizations have risen and fallen based on the state of their soils," Sparks said. "Our future security really depends on our ability to take care of what's beneath our feet."

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