Soil erosion, combined with the effects of climate change and the loss of agricultural land to urban sprawl, will threaten global food security unless drastic action is taken to preserve the fertility of the world’s farmland, warns a paper published on May 7th in the journal Science. Soil provides the basis for agriculture, improves water quality and stores carbon. However, human activities are depleting Earth’s soil resources. According to the authors, unsustainable farming practices have accelerated the loss of soil through erosion and nutrient removal. Agriculture is therefore a major game-changer for the long-term health of soil - the “living epidermis” of the planet. Lead author Ronald Amundson, a professor at the University of California, Berkeley, said that “Ever since humans developed agriculture, we’ve been transforming the planet and throwing the soil’s nutrient cycle out of balance.” People are often not aware of the geological transformation because the changes happen slowly, he explained. Soil erosion has increased since the “green revolution” with its intensive use of chemicals and fertilisers. Although these methods helped to significantly increase crop yields, the ability of soil to support the growth of our food supply is now reaching a peak. The authors note that most of the Earth’s fertile soils are already in agricultural production. In addition, urbanisation is eating up productive farmland. Between 1970 and 2000, an area of agricultural land the size of Denmark became urbanised. Over the next 20 years, 1.5 million square kilometres of land, an area the size of Mongolia, will be converted to urban areas, the scientists warn. The supply of nitrogen, potassium and phosphorous, the three main fertilisers, could also become a major political challenge and lead to uncertainties. The nitrogen synthesis process is energy-intensive, making its supply dependent on fossil fuels. Phosphorous and potassium come from rocks and minerals which are not equitably distributed throughout the world. The authors point out that the United States has only 1 to 2% of global potassium reserves and its phosphorous reserves are expected to run out in about three decades. “Morocco will soon be the largest source of phosphorus in the world, followed by China,” Dr Amundson said. „These two countries will have a great deal of say in the distribution of those resources. Some people suggest we will see the emergence of a phosphorus cartel.” The authors call for a better management of soils. One proposal is to recycle nutrients captured in waste treatment facilities in the same way that paper and plastics are recycled from domestic waste, Dr Amundson said. “The nutrients lost can be captured, recycled and put back into the ground. Additionally, more efficient management is needed to reduce losses from soil. Excess nitrogen, for example, is considered a pollutant, with the runoff sapping oxygen from the nation’s waterways, suffocating aquatic life and creating dead zones in coastal margins. (ab)