The state we are in – understanding the life-cycle of soils
19 May 2006
Soil problems have global consequences for food security, poverty reduction, water protection and biodiversity.
In 2001 the European Commission indicated that soil loss and declining soil fertility were a main threat to sustainable development, because they diminish the viability of agricultural land. Some soil protection is undertaken through various policy areas but a comprehensive European Community soil protection policy does not exist. It has now become evident that soil problems have global consequences for food security, poverty reduction, water protection and biodiversity. Concerted approaches are therefore needed for providing solutions.
This is not the first time in geological history that soil loss is a world wide problem. Two hundred and fifty million years ago, the Permian-Triassic mass extinction occurred – the biggest extinction of all time. At that time, greenhouse gases were injected into the atmosphere by gigantic volcanic eruptions in Siberia, causing the runaway greenhouse effect that triggered the mass extinction. The rising temperatures, together with increased concentrations of green-house gases, caused acid rain that killed the vegetation on land and the soils were washed into the sea.
Soil degradation has been the most frequent cause of cultural decline and total civilisation collapse
More recently, the world’s first civilisation – the Sumer from Southern Mesopotamia, which is now Iraq – collapsed around 2000 BC as a result of soil degradation. Subsequently, soil degradation has been the most frequent cause of cultural decline and total civilisation collapse. But in the past, civilisation collapses were localised to certain geographical areas. Today, with six billion inhabitants on Earth who are intertwined in global trade, the looming collapse is likely to be global.
While we have an overview of what is causing soil degradation world wide, our understanding of soil formation processes and rates are still poor. Soil – while strictly speaking a renewable resource – has formation rates that are very slow, while degradation rates are much higher. How much higher is not well known.
A special issue of Science on 11 June 2004 claimed soil to be the most complicated biomaterial on the planet. It is a composit of minerals (rock weathering products) and organic matter (decomposing plant material), and the fertility of the soil is dependent on the level of its mineral and organic content. Threats to soil degradation include erosion, decline in organic matter and soil contamination. It has been estimated that 52 million hectares of land in the EU are affected by degradation process, 16% of the total land area in the EU. Soil degradation in dry areas is known as desertification, which is a major problem in many of the Mediterrainean regions. World wide, desertification can cause the destabilisation of societies and migration of human populations, and has thus extremely serious socio-economic consequences.
Natural processes such as wind and water induce soil erosion by removing soil and transporting it elsewhere. However, human activities can dramatically increase erosion rates. Man-made erosion has been estimated to be an order of magnitude higher (100 gigatonnes/year) than natural erosion, roughly 50% of which is due to inappropriate agricultural practices. Man has thus become a geological force! Erosion is enhanced by steep slopes, climate, inappropriate land use, land-cover patterns and ecological disasters. The results of soil erosion are the loss of soil functions and ultimately the loss of soil itself. In parts of the Mediterranean the erosion is as high as 200 mm/100 years and in Africa a staggering rate of 2,000 mm/100 years is reported.
The world has grown too small to forgive us any big mistakes
Organic matter plays a central role in maintaining key soil functions and is an essential determinant of erosion resistance and soil fertility. The European Soil Bureau has estimated that 75% of the total area analysed in south Europe has a low (3.4%) or very low level of (1.7%) soil organic matter – agronomists consider soils with less than 1.7% organic matter to be in pre-desertification stage. The percentage of soils in Europe with less than 2.6% organic matter rose from 35% to 42% in the period 1980-1995. Organic carbon loss in England and Wales over the past quarter of a century is as high as 16%, or 4.4 million tonnes of carbon per year. Globally, more than twice as much carbon is held in soils as in vegetation and the atmosphere combined and soil protection is thus a major issue for the buffering of climate change.
Soil is the product of complex interactions between climate, geology, vegetation, biological activity, time and land use. Average world soil formation rates, based on the conversion of parent rock into soil, are estimated to be between 0.05 and 10 mm/100 years. These numbers have large error bars. Within this uncertainty range, soils of agricultural land most often result in a net loss.
Scientists in the US and their European counterparts now wish to establish research networks that are collaborative and focus on understanding the biological, chemical and physical processes in the Critical Zone (from treetop to bedrock) that control the atmosphere, biota, landforms and water supplies. This can be done most effectively by establishing ‘Soil Observatories’, where common measurements are undertaken in regions that differ with respect to geology, climate, landscape and anthropogenic influence.
To this end, the National Science Foundation in the US has provided funding for instrumentation at five field sites; the effect of biota on weathering will be studied in the next five years by Ragnarsdottir and her colleagues in Bristol, Sheffield and Leeds, funded by a Natural Environment Research Council consortium grant; and theWorldwide Universities Network (WUN) will assist the European community to establish a link with their activities so that weathering and soil formation can be understood at the global scale and these results used to underpin soil protection policy.
In the words of Ronald Wright, “the future of everything we have accomplished since our intelligence evolved will depend on the wisdom of our actions over the next few years. Humans on Earth have a presence so colossal that error is a luxury we can no longer afford. The world has grown too small to forgive us any big mistakes.”