We lose 5–10kgs of soil for every meal we eat. Every person, every meal, every day. This works out to around 75 billion tonnes of soil lost every year based on numbers from the US Geological Service. At this rate, we have around 60 years of farmable topsoil left. Within our lifetimes, we will have lost most if not all of the productive soils we now rely on for our food. But how do we ‘lose’ soil?
What is soil?
First things first, what is soil and why is it important? Most definitions of soil is that it is the top layer of earth that is conducive to plant growth. Soil can have many different chemical and physical structures, but generally features higher carbon levels and is much more biologically active.
In an agricultural context, the loss of topsoil means that farm lands are less fertile and support lower crop yields. If a farm loses too much of its precious soil, it is very likely that the farm will become unviable, and the potential food production is lost. If this happens at a large scale across regions or states, food security of the region can be servery impacted.
How do we lose soil?
Losing soil can have a serious impact of our ability to produce food, but what does it mean to lose soil, and how does it happen?
There are many ways we lose soil, and they can all be characterised as mismanagement of natural cycles. This can be broken down into Cultural, Chemical or Biological in nature.
Cultural
Cultural mismanagement of soils includes are the negative interactions that humans have with the land. This includes deforestation, over tilling, compaction, irrigation mismanagement, and overgrazing. Cultural mismanagement also includes urbanisation and urban encroachment of farm land.
Chemical
Chemical mismanagement of soils includes the reduction of soil organic matter (OM) and carbon, increased salinity, chemical and plastic contamination, nitrogen, mercury and heavy metal contamination.
Biological
Biological degradation of soils can include the introduction of weeds that destroy natural systems, overgrazing of domestic, commercial and pest animals, particularly hard hooved animals on wet soil. Biological impacts can also include destruction of soil bacteria, flora and fauna through changes in the ecosystem.
These three main drivers of soil degradation all interact to reduce the stability and increase the movement of soil, either through water or wind erosion.
A story of soil loss.
A new farmer needs land to feed his family. The new farmer cuts and burns the native forests. The loss of trees and plants that helped stabilise the land makes the soil more transient and prone to runoff. But because of the decades of forest cover and depositions of organic matter, the topsoil is deep and can deal with a little bit of run off while it recovers. But it can’t. Now that the land is open, the farmer can run some cattle. The cattle preferentially graze the sweet native grasses, leaving unpalatable grasses and weeds to take over. The hard hooved cattle compact and pug up the wet soil, destroying soil structure, and with lower levels of ground cover, the soil is more susceptible to wind and water erosion. The farmer changes his system to try growing grains. He takes the cattle off, sprays non-selective herbicide on the remaining plants to leave bare soil. He then comes in with a heavy tractor and tills the land to create a nice, uniform seed bed for his planter. The soil dries out with no ground cover and when the wind blows, the soil is lifted off the farm and into the atmosphere, most likely ending up in the ocean. But because the soil is deep, the farmer can continue to do this for years. He adds synthetic fertilisers to boost production and kills his weeds with chemicals of various modes of action to reduce the risk of the weeds becoming resistant. This changes the soil biology. This model works for several years and his yields are great, but year on year he is losing soil to wind and water erosion. Eventually the soil slowly starts to become more and more infertile until it no longer supports his business so he sells the farm and moves into town. The impact of the farmer on the land is that provision of years of food for the rest of his community, at the expense of the environment and soil resources.
How do we fix it?
Improving and saving agricultural soils centres around practices that increase the organic matter and carbon in the soil. To save soil and improve the environmental sustainability of agriculture, we need to preserve the existing soil resources. This will involve the intensification of production on the land we currently farm and preservation of native forests. On the lands we are farming, an intensive no-till and cover cropping management strategy needs to be implemented to start to rebuild soils from the ground up. The carbon from the organic matter incorporates into the soils to help to improve the land and increase fertility. Following sustainable grazing practices is also critical on neglected grazing land. It is possible to rebuild carbon in the soil through the use of cattle on the right landscape. We need to reduce the spread of urban development into prime agricultural land to ensure that the potential production of these farms are not lost to urban sprawl.
Finally, the choices you make as a consumer have an incredible impact on the types of agricultural systems we use. Agribusinesses are agile and will change to meet consumer expectations, as a community we have the responsibility to purchase sustainably produced food that aligns with our beliefs of what sustainable agriculture is. But to make informed decisions, consumers need to be informed.