The United Nations has completed the first global assessment of the state of the planet's land resources, finding in a report Monday that a quarter of all land is highly degraded and warning the trend must be reversed if the world's growing population is to be fed.

The UN Food and Agriculture Organization estimates that farmers will have to produce 70 per cent more food by 2050 to meet the needs of the world's expected 9 billion-strong population. That amounts to 1 billion tons more wheat, rice and other cereals and 200 million more tons of beef and other livestock.

But as it is, most available land is already being farmed, and in ways that often decrease its productivity through practices that lead to soil erosion and wasting of water, the report said.

That means that to meet the world's future food needs, a major "sustainable intensification" of agricultural productivity on existing farmland will be necessary, the FAO said in State of the World's Land and Water Resources for Food and Agriculture.

FAO's director-general Jacques Diouf said increased competition over land for growing biofuels, coupled with climate change and poor farming practices, had left key food-producing systems at risk of being unable to meet human needs in 2050.

"The consequences in terms of hunger and poverty are unacceptable," he told reporters at FAO's Rome headquarters. "Remedial actions need to be taken now. We simply cannot continue on a course of business as usual."

The report was released Monday, as delegates from around the world meet in Durban, South Africa, for a two-week UN climate change conference aimed at breaking the deadlock on how to curb emissions of carbon dioxide and other pollutants.

The report found that climate change coupled with poor farming practices had contributed to a decrease in productivity of the world's farmland following the boom years of the Green Revolution, when crop yields soared thanks to new technologies, pesticides and the introduction of high-yield crops.

Thanks to the Green Revolution, the world's cropland grew by just 12 per cent between 1961 and 2009, but food productivity increased by 150 per cent. But the UN report found that rates of growth have been slowing down in many areas and today are only half of what they were at the peak of the Green Revolution.

The price tag deemed necessary for investments through 2050 is $1 trillion US in irrigation water management alone for developing countries, with another $160 billion for soil conservation and flood control.

It found that 25 per cent of the world's land is now "highly degraded," with soil erosion, water degradation and biodiversity loss. Another 8 per cent is moderately degraded, while 36 per cent is stable or slightly degraded and 10 per cent is ranked as "improving."

The rest of the Earth's surface is either bare or covered by inland water bodies.

Some examples of areas at risk:

  • Western Europe, where highly intensive agriculture has led to pollution of soil and aquifers and a resulting loss of biodiversity;
  • In the highlands of the Himalayas, the Andes, the Ethiopian plateau and southern Africa, soil erosion has been coupled with an increased intensity of floods;
  • In southeast and eastern Asia's rice-based food systems, land has been abandoned thanks in part to a loss of the cultural value of it.

The report also found that water around the world is becoming ever more scarce and salinated, while groundwater is becoming more polluted by agricultural runoff and other toxins.

In order to meet the world's water needs in 2050, more efficient irrigation will be necessary since currently most irrigation systems perform well below their capacity, the FAO said.

The agency called for new farming practices like integrated irrigation and fish-farm systems to meet those demands, as well as overall investment in agricultural development.

The price tag deemed necessary for investments through 2050 is $1 trillion US in irrigation water management alone for developing countries, with another $160 billion for soil conservation and flood control.