A tractor prepares a field by turning over the cover crop into the soil in preparation for planting at Leafy Greens, in the Salinas Valley, California, June 2011. Cover crops of barley and rye grass hold the topsoil, reducing erosion. Photo: Lance Cheung / USDA Media via Flickr (CC BY-ND).
Conserving soil: precious, finite and under threat
5th August 2015
Human existence relies on healthy soils, writes Jane Rickson. But all over the world they are being lost and degraded by inappropriate land use, reducing their capacity to produce food and store water, nutrients and carbon. Sustainable land management must be incentivised to conserve this essential resource.
Our very survival depends on this very thin layer of soil that is found in only a small fraction of the earth's surface. Moreover slow rates of soil formation mean soil is effectively a finite and limited resource.
Healthy soils deliver a wide range of ecosystem goods and services that can be linked to human well-being and national economic status.
At a time when global demand for food is increasing, protecting soil resources is at the heart of future food security, as over 94% of our food comes from soil.
Soil is also the source of fibre, fodder and (bio)fuel production and offers a habitat to diverse flora and fauna that are the foundation of the food chain. Soil stores water to reduce the impacts of flooding and droughts that are predicted to increase under future climate change scenarios.
Soils also hold vast amounts of carbon, which helps mitigate the effect of greenhouse gas emissions and associated global warming.
In short, our very survival is dependent on this very thin layer of soil that is found in only a small fraction of the earth's surface. Moreover slow rates of soil formation mean soil is effectively a finite and limited resource.
Global soils are under increasing pressure from external drivers such as demands for more food production (quantity, quality and reliability), the intensification of agriculture, urbanisation (leading to sealing of soil surfaces, as well as migration of workers away from agricultural areas), and extreme weather events.
These factors are leading to soil degradation, manifest in processes such as soil erosion, compaction, loss of organic matter and soil biodiversity, and contamination. Every year, an estimated 12 million hectares of agricultural land are lost to soil degradation, adding to the billions of hectares that are already degraded.
Degraded soils deliver fewer goods and services, and are less resilient to external pressures. Hence a damaging, often irreversible positive feedback loop is set up.
The impact of 'land mining' on future food production
Increased agricultural intensification may aggravate the risk of soil degradation. Cropped land is particularly vulnerable to soil erosion, compaction and loss of organic matter and biodiversity.
This is due to the exposure of bare soil for lengthy times of the year, the disturbance of soil structure and biology during farming operations such as tillage, the increasing weight of larger agricultural machinery, the number of repeated passes over a parcel of land and the removal of organic matter during harvests.
Globally, an estimated 2 to 5 million hectares of arable land are lost every year to soil erosion alone. Concerns are growing that soil degradation is reducing the productive capacity of our land, with devastating impacts. Some estimate a 30 % reduction in food production due to degradation of agricultural land by 2040.
This has serious implications for food security worldwide and our ability to produce food that can meet cultural, health and nutritional needs, food that's available, accessible and affordable, both now and in the future.
At present, the evidence base is limited in identifying direct impacts of soil degradation on food production. This is partly because some soil management practices have been used to mask these impacts.
These include adding chemical fertilisers to soil to replace lost nutrients, applying irrigation to compensate for the reduced water holding capacity of thin, eroded soils, or introducing higher yielding crop varieties. Many of these practices rely on finite resources and require large capital investments. They have little effect on the resilience of soil to resist (and recover from) degradation processes.
Incentivising farmers to protect and revive their soils for the long-term
By definition, soil degradation decreases the ability of soils to function, but the corollary is that soil protection and conservation should improve soil condition and enhance the delivery of ecosystem goods and services including food production. Existing and innovative land and water management can prevent and reverse soil degradation.
Many mitigation measures can be effective in controlling multiple degradation threats. For example, increasing soil organic matter content will reduce the susceptibility of soil to erosion and compaction, whilst providing the substrate for an active microbial community.
Organic matter improves soil structure, water holding capacity and resilience to resist and recover from external pressures, such as extreme weather events and overexploitation of land over time.
Farmers can increase soil organic matter content by reducing tillage intensity, planting cover crops, adding organic amendments and composts, and retaining crop residues within the field, rather than removing or burning them after harvest.
However, conserving soil and reversing soil degradation is challenging. The beneficial effects of soil conservation practices on soil condition are often only apparent after several years. Clearly, this is at odds with the much shorter term economic cycle faced by many farmers.
Some practices may result in yield reductions in the short term, which can make farming uneconomic, especially in marginal areas. Nevertheless, the impacts and costs of continuing soil degradation such as food shortages will be felt by society as a whole, not just the farming sector.
So, policies are urgently needed to incentivise farmers to protect soils so this precious natural resource can continue to deliver vital goods and services for generations to come.
Jane Rickson is Professor of Soil Erosion and Conservation in Cranfield University's Soil and AgriFood Institute. She has 30 years experience of research, consultancy and training in land and water engineering, and soil management. Her work has focussed on the causes and effects of land degradation, with particular emphasis on soil erosion and its control.
Rickson et al. (2015) 'Input constraints to food production: the impact of soil degradation'.
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