A landscape of soil degradation after the floods, Nsanje District, Malawi.
The world's soils are rapidly deteriorating due to soil erosion, nutrient depletion, loss of soil organic carbon, soil sealing and other threats, but this trend can be reversed provided countries take the lead in promoting sustainable management practices and the use of appropriate technologies, according to a new UN report released today.
The Status of the World's Soil Resources produced by FAO's Intergovernmental Technical Panel on Soils brings together the work of some 200 soil scientists from 60 countries. Its publication coincides with World Soil Day which is celebrated on 4 December and also the end of the UN International Year of Soils 2015 an initiative which has served to raise global awareness on what has been described as "humanity's silent ally".
"Let us promote sustainable soil management rooted in proper soil governance and sound investments. Together, we can promote the cause of soils, a truly solid ground for life," UN Secretary-General Ban Ki-moon said in a message for World Soil Day.
Soils are vital for producing nutritious crops and they filter and clean tens of thousands of cubic kilometres of water each year. As a major storehouse for carbon, soils also help regulate emissions of carbon dioxide and other greenhouse gases, thus fundamental for regulating climate.
Yet the overwhelming conclusion of the report is that the majority of the world's soil resources are in only fair, poor or very poor condition and that conditions are getting worse in far more cases than they are improving. In particular, 33 percent of land is moderately to highly degraded due to erosion, salinization, compaction, acidification, and chemical pollution of soils.
"Further loss of productive soils would severely damage food production and food security, amplify food-price volatility, and potentially plunge millions of people into hunger and poverty. But the report also offers evidence that this loss of soil resources and functions can be avoided," said FAO Director-General José Graziano da Silva.
Writing the foreword to the 650 page-long report, he expressed the conviction that the contents will "greatly assist in galvanizing action at all levels towards more sustainable soil management," adding that this was in line with the international community's commitment to achieve the Sustainable Development Goals.
The impact of population growth, urbanization and climate change
Changes to the condition of soils are primarily driven by population growth and economic growth, factors that are expected to persist in the decades to come.
The report notes how to feed a global population that has grown to some 7.3 billion today, over 35 percent of the Earth's ice-free land area has been converted to agriculture. The result is that soils that have been cleared of natural vegetation to grow crops or graze livestock suffer from sharp increases in erosion and steep losses in soil carbon, nutrients and soil biodiversity.
But urbanization is also taking a major toll. The rapid growth of cities and industries has degraded increasingly wide areas, including by contaminating soils with excess salt, acidity and heavy metals; compacting them under heavy machinery; and sealing them permanently under asphalt and concrete.
Climate change - which is currently the focus of the UN COP21 conference in Paris - is a further strong driver of soil change, the report finds.
Higher temperatures and related extreme weather events such as droughts, floods and storms impact on soil quantity and fertility in a number of ways, including reducing moisture and depleting the layers of nutrient-rich topsoil. They also contribute to an increase in the rate of soil erosion and shoreline retreat.
Achieving healthy soils
The report focuses on the 10 main threats to soil functions: soil erosion, soil organic carbon loss, nutrient imbalance, soil acidification, soil contamination, waterlogging, soil compaction, soil sealing, salinization and loss of soil biodiversity.
It notes how there is a general consensus on soil-related strategies that can, on the one hand, increase the supply of food, while on the other, minimize harmful environmental impacts.
The solution proposed is one that centres on sustainable soil management and which requires the participation of a broad level of stakeholders ranging from governments to small-holder farmers.
Erosion, for example, can be curbed by reducing or eliminating tillage - digging, stirring, and overturning of soil - and using crop residues to protect the soil surface from the effects of rain and winds. Similarly, soils suffering from nutrient deficits can be restored and yields increased by returning crop residues and other organic material to the soil, employing crop rotation with nitrogen-fixing crops, and making judicious use of organic and mineral fertilizers.
The report identifies four priorities for action:
• Minimize further degradation of soils and restore the productivity of soils that are already degraded in regions where people are most vulnerable;
• Stabilize global stores of soil organic matter, including both soil organic carbon and soil organisms;
• Stabilize or reduce global use of nitrogen and phosphorus fertilizer, while increasing fertilizer use in regions of nutrient deficiency; and,
• Improve our knowledge about the state and trend of soil conditions.
Such actions need to be supported by targeted policies, including:
• support for the development of soil information systems to monitor and forecast soil change;
• increasing education and awareness on soil issues, by integrating this into formal education and across the curriculum - from geology to geography, from biology to economics.
• investing in research development and extension, to develop test, disseminate sustainable soil management technologies and practices.
• introducing appropriate and effective regulation and incentives. This could include taxes that discourage harmful practices such as excessive use of fertilizer, herbicides and pesticides. Zoning systems can be used to protect the best agricultural soil from urban sprawl. Subsidies could be used to encourage people to purchase tools and other inputs that have a less harmful impact on soils, while certification of sustainable crop and livestock practices can make produce more commercially attractive at higher prices.
• supporting achievement of local, regional and international food security by considering countries' soil resources and their capacities to manage them sustainably.
Some of the report’s key findings:
Erosion carries away 25 to 40 billion tonnes of topsoil every year, significantly reducing crop yields and the soil’s ability to store and cycle carbon, nutrients, and water. Annual cereal production losses due to erosion have been estimated at 7.6 million tonnes lost each year. If action is not taken to reduce erosion, a total reduction of over 253 million tonnes of cereals could be projected by 2050. This yield loss would be equivalent to removing 1.5 million square kilometres of land from crop production – or roughly all the arable land in India.
Lack of soil nutrients is the greatest obstacle to improving food production and soil function in many degraded landscapes. In Africa, all but three countries extract more nutrients from the soil each year than are returned through use of fertilizer, crop residues, manure, and other organic matter.
Accumulation of salts in the soil reduces crop yields and can completely eliminate crop production. Human-induced salinity affects an estimated 760,000 square kilometres of land worldwide – an area larger than all the arable land in Brazil.
Soil acidity is a serious constraint to food production worldwide. The most acidic topsoils in the world are located in areas of South America that have experienced deforestation and intensive agriculture.
• Summary - The State of the World's Soil Resources
• Full report