Like most aspects of our natural world, we take fertile topsoils rich in organic carbon for granted. We don't realize how fragile this thin layer is which covers only a small fraction of earth's crust. We humans, along with many of our terrestrial fellow species, are dependent on fertile topsoil to survive, especially at our current levels of population and development.1 Only 7% of the earth’s surface has topsoil suitable for agriculture. The rest is mountains, oceans, lakes, deserts and polar regions. In modern times, we’ve buried and destroyed a lot of our topsoil under our cities, roads, industrial parks, landfills and shopping centers.
Topsoil is a mix of decomposed biological matter (organic carbon) from above and minerals from below. It takes about 500 years, in an undisturbed temperate forest or prairie, for natural processes to create one centimeter of topsoil. By comparison, it takes us only two and a half years, on average, to destroy one centimeter of topsoil. Modern farming methods, including tillage and the large scale use of mineral fertilizers, pesticides and herbicides, cause both the erosion and oxidation of topsoil.
Oxidation, in this case, means that the organic carbon in soil, the element that makes it black and fertile, is converted to carbon dioxide at a rate that is much more rapid than it is replenished. One third of the excess carbon in the atmosphere has been emitted from topsoil as a result of human activity.
Not only is topsoil thinning, but we are losing 4 million hectares of topsoil covered land per year to desertification, which is an area the size of Switzerland, or twice the area of the American state of Massachusetts. Desertification means that the rock, sand and clay under the vanishing topsoil layer is exposed, and the habitat the topsoil supported disappears. It can and does occur in any climate, whether arid, semi-arid, tropical or temperate. Whatever agricultural topsoil we have left is rapidly losing its organic carbon content.2 Organic carbon is essential for soil fertility, retaining nutrients and water while improving nutrient uptake and buffering soil pH and salinity.3
Topsoil forms most easily in temperate regions of the world with winter seasons that slow the decomposition rate down to allow humic matter to slowly accumulate in soil. In warmer regions, almost all organic matter decomposes immediately to CO2, in a matter of weeks. It is instructive to note that the developed nations with stable societies are in regions of the world with temperate climates. These countries have inherited a geological legacy of fertile soils rich in organic carbon, but this inheritance has largely been, and continues to be squandered. Those regions that lack organic carbon in their soils tend to be plagued with poverty, malnourishment, instable societies and governments, and a lack of development, education and health care. Unless our soil management practices change, this is where we are all headed.
Soil organic carbon, that black stuff in our dirt, is the foundation of wealth in our world. It is the foundation of our stable societies, of our scientific and technological development. This essential foundation is being lost. From 1955 to 1995, soil erosion and degradation caused farmers to abandon some 430 million hectares, one third of all arable land, which is the area of India and China combined.7 The Food and Agriculture Organization of the United Nations estimates we have only about 30 years left until agricultural productivity begins to decline from a lack of fertile topsoil. Those of us in the developed world haven't noticed it yet, but many areas of the world have already experienced severely diminished to devastated agricultural capability due to soil carbon and topsoil loss.
Societies throughout history have made their living farming, and one of the strange things about the history of farming is that it has resulted in long-term soil degradation in society after society. In the end, the soil was not able to support them over the long run.
So in a very real sense the history of humanity, as a post glacial exercise in expansion via agriculture, has had this sort of dark side that has undermined the sustainablity of farming practices that we rely on to maintain the continuity of civilizations.8 9
In modern times, we have come to believe wealth springs from our financial systems, our technological advances, our well organized societies, our intelligence. But take the carbon rich topsoil out from under our feet and our food chain collapses, most likely to the point where our population, wealth, our technological development, our societal order all collapse with it. In certain regions of the world where topsoil is vanishing, this collapse is apparent, a driver of migration, poverty and social instablity.
In more developed regions, as soil and thus food quality have declined, human health and productivity have been undermined.
Regenerative small scale farming, with a focus on integrated rotational grazing and no-till cropping, is a relatively simple solution that can rapidly restore soil organic carbon and fertility.10 Biochar can play an important role in regenerative agriculture. If we are going to preserve our soils, a signficant portion of the large scale, industrialized farming we currently practice must be abandoned. As with fossil fuels, we ultimately don't have a choice. Either we can plan ahead and start modifying our agricultural practices now, or risk that we undermine our capacity to provide sufficient food for ourselves.