Topsoil has eroded from a third of farmland globally. Without topsoil, land loses its capacity to grow crops or provide grazing for animals. We have the knowledge to restore fertility, but implementing it needs a concerted effort.
UN Sustainable Development Goal (SDG) 15.3 to achieve land degradation neutrality by 2030 is behind schedule. In fact, we are losing 12 million hectares of topsoil (roughly the size of New York State) globally every year according to the United Nations Convention to Combat Desertification (UNCCD). That’s more than ever before.
Topsoil is the nutrient-dense, uppermost layer of soil, and it is crucial for food security – without it, land can support little plant growth. Erosion, a form of land degradation, is the displacement of this soil as it is washed or blown away. Topsoil erosion is a particular challenge in agriculture, which can offer both causes and solutions to the problem. Here’s what you need to know.
1. Which regions are most affected?
Land degradation and erosion already affect over a billion people worldwide, but the situation varies strongly by region. Hot, dry and windy areas are most affected because they support less vegetation. The Middle East, the Mediterranean and sub-Saharan Africa in particular have seen a marked expansion of dry areas. More and more people are living in vulnerable areas.
The issue is most alarming in emerging economies. In contrast to developed countries, few have policies in place to combat erosion or support more sustainable farming methods. At the same time, growing populations in these countries make the need for food security most urgent. In order to survive, smallholder farmers may be forced to clear erosion-prone areas like steep slopes in order to grow more crops.
2. What are the biggest dangers?
The top five to twenty centimeters of soil have better water retention and hold more nutrients and micro-organisms – more biodiversity – than deeper layers of soil. It can take one thousand years for a centimeter of new soil to form. When healthy topsoil erodes faster than it is formed, farmers need to spend more and more on fertilizers to maintain productivity.
In extreme cases, production can eventually drop to the point where a field will no longer grow crops or provide grazing pasture for livestock. Farmers who can no longer make a living from their land are forced to leave. These environmental migrants usually end up in the nearest cities.
Under humid conditions and with tree cover, vegetation re-covers the abandoned land fast – with plant matter returning to the soil – but this process can take decades in semi-arid and arid environments. In the latter case, erosion is a vicious cycle: fewer plants mean fewer roots holding onto the soil, making the soil still more susceptible to erosion.
3. What are the main agricultural causes?
Some erosion of farmland is inevitable, with sandy soils most vulnerable to wind erosion and loamy soils to water erosion. However, it is exacerbated by a wide range of agricultural practices: first and foremost, the removal of vegetation cover. Farming on slopes, local rainfall patterns, growing certain types of crop, and land management are also important factors.
Camels looking for food in the Judean Desert, Israel.
Overgrazing by livestock is perhaps most damaging of all, particularly on steep terrain in arid and semi-arid climates. As fewer plants grow because they are eaten or trampled by the animals, the soil is exposed to wind and water erosion and to the heat of the sun. As the soil dries, it becomes even easier to erode. Trampling also causes the soil to compact, which reduces water infiltration and increases runoff.
Plowing agricultural land is another factor. The practice destroys weeds, but it also leaves soil unprotected and stirs up the topsoil, disturbing the soil organisms, which are crucial to feeding growing crops. The heavy machinery used can cause compaction of the subsoil, again reducing infiltration.
Field size is also key. Accumulating rainwater can cause more damage on the super-scale fields of industrial agriculture, particularly on sloping land. Field size could be reduced by terracing, building barriers and growing hedges, but these techniques are often abandoned for efficiency reasons.
Contour planting – following the natural lines of a slope – helps reduce water runoff.
4. What else can be done to protect farmland?
Data on exactly how much agricultural land is lost to erosion has, until recently, been hard to come by. This has led some countries to almost literally bury their heads in the sand. That is now changing thanks to remote sensing. Through the UNCCD, the Group of Earth Observations is making satellite data publicly available. That transparency should provide more countries with the impetus to tackle the issue.
At the farm level, the ancient soil-replenishing practices of crop rotation, mixed cropping and leaving land fallow are better for farmland than the monocultures of the last 70 years. Systems like integrated crop-livestock-forestry (iCLF), which is being rolled out in Brazil, are also showing promising results.
To avoid leaving the land bare and vulnerable after harvest, more and more farmers plant ‘cover crops’ like mustard. This approach is expensive but doubly beneficial: it creates protective ground cover, and it can be plowed under in spring, increasing the amount of nutritious organic matter in the soil.
A growing number of farmers eschews plowing altogether. Undisturbed topsoil retains more moisture and higher biodiversity. In Australia, over 90 percent of farmers now use no-till methods and the practice is gaining popularity in countries that practice large-scale agriculture, including the US and Brazil. Farmers transitioning to the system may need to bridge a period of lower production and invest in specialist planting machines, but the practice saves money on labor and fuel costs.
Terraced ride paddies in Thailand
Drip-irrigation systems, or building terraces, rain barriers and swales to collect rain water, are long-term solutions, but require a high initial investment. Reforestation projects are also costly and need ongoing maintenance to make sure the young trees flourish. Obviously, land planted for trees can no longer be used to grow crops like cereals. However, reforested areas provide invaluable biodiversity, roots to hold rainwater, and barriers to wind erosion and the expansion of dune fields.
NGOs like Living Land and Commonland take a holistic approach to the issue, backed by far-sighted philanthropic funds and governments. Not only do they aim to reverse erosion and restore landscapes, they want to make farms profitable again, key if they are to be sustainable and draw people back to the land.
Overall, it’s important to remember that erosion is site and situation dependent: there is no one-size-fits-all solution.
5. What are the main challenges to tackling erosion?
Farmers may feel forced to adopt unsustainable measures in order to pay their loans and survive financially. Many of the alternatives are costly or could reduce production, at least in the short term. Long-term thinking is therefore needed to look beyond the immediate costs to the added value that soil preservation would bring.
Some financial support, such as the Common Agricultural Policy subsidies in Europe, has tended to incentivize increased production over sustainability. For instance, in some regions in Spain, oranges were traditionally planted close together on terraced fields and picked by hand. As the price of the fruit dropped, growers in Spain sold their land to big agri-industrial companies. The companies received hefty subsidies to replant trees and install irrigation. They removed the terraces to create larger, sloped fields with wide avenues between the fruit trees to enable machine picking. The result? Erosion.
6. What needs to happen now?
Like any complex issue, tackling erosion requires seemingly paradoxical solutions. We have the knowledge to solve the issue, but farmers need better land management advice and ongoing support – both financial and knowledge-based – to try new approaches and technological solutions.
We need changes and incentives at a policy level, while solutions must be site-specific. And forcing measures on farmers from above will lead to resistance; a bottom-up approach is needed to ensure local ownership of projects and long-term success.