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Peak Soil 

In the past 40 years, 30 percent of the planet's arable land has become unproductive due to erosion
 
The process of raising the world’s food has not always been kind to the environment. Many of the adverse environmental impacts caused by agriculture are results of either the loss of natural habitat that occurs when land is converted to agricultural purposes and use (or misuse) of pesticides and fertilizers. 
 
Yet soil degradation has also been a factor, and one with implications for food production as well.
 
the dirt beneath our feet is a miracleThe dirt beneath our feet is a nearly magical world filled with tiny, wondrous creatures. A mere handful of soil might contain a half million different species including ants, earthworms, fungi, bacteria and other microorganisms. Soil provides nearly all of our food - only one percent of our calories come from the oceans.
 
Soil also gives life to all of the world's plants that supply us with much of our oxygen, another important ecosystem service. Soil cleans water, keeps contaminants out of streams and lakes, and prevents flooding. Soil can also absorb huge amounts of carbon, second only to the oceans.
 
The losses
 
Each year, 12 million hectares of land, where 20 million tonnes of grain could have been grown, are lost to land degradation. In the past 40 years, 30 percent of the planet's arable (food-producing) land has become unproductive due to erosion.
 
Most soil erosion – about two thirds – is caused by water washing away topsoil, with another third caused by wind. Ploughing, removal of crop residues after harvest, and overgrazing all leave soil naked and vulnerable to wind and rain, resulting in gradual, often unnoticed erosion of soil. 
 
Farmland can be degraded in several other ways besides erosion. Physical degradation from mechanical tilling can lead to soil compaction and crusting. Repeated cropping without sufficient fallow periods or replacement of nutrients with cover crops, manure, or fertilizer can deplete soil nutrients. In addition, over-application of agricultural chemicals can kill beneficial soil organisms.

Poor water management on irrigated cropland is a leading cause of degraded farmland. Inadequate drainage can lead to waterlogging of the soil or to salinization, in which salt levels build up in the soil to toxic levels. With some 10 to 15 percent of all irrigated land suffering some degree of waterlogging and salinization, these two problems alone represent a significant threat to the world’s productive capacity.

Often, when climate and human activities combine to turn once-healthy soil into wasteland, the degradation is seemingly irreversible. 
 
Reversing the soil conditions
 
A big part of reversing soil decline is the use of carbon, the same element that is helping to overheat the planet if we want to continue to eat, drink and combat global warming.
 
The more of a crop - maize, soy or vegetable - that remains after harvest, the more carbon is returned to the soil. This carbon is mainly found in humus - the rich organic material from decay of plant material. Soil needs to contain just 1.5 percent carbon to be healthy and resilient - that is, more capable of withstanding drought and other harsh conditions. Healthy soil equals healthy crops, healthy livestock and healthy people.
However, most soils suffer from 30 to 60 percent loss in soil carbon. 
 
Farmers and pastoralists could perform "miracles" in keeping carbon in the soil and helping to pull carbon out of the atmosphere and feed the world - if they were properly supported.
 
Carbon absorbtion
 
A huge amount of carbon from the atmosphere could be sequestered in soil. When a plant grows, it takes CO2 out the atmosphere and releases oxygen.
 
The world's 3.4 billion hectares of rangeland and pastures has the potential to sequester or absorb up to 10 percent of the annual carbon emissions from burning fossil fuels and cement production.
 
However, the contradictory view is that determining exactly how much carbon a farm field or pasture can absorb from the atmosphere is highly variable and difficult to determine. Proper land management can help with climate change but in no way does it reduce the need to make major reductions in fossil fuel use. And using farmland or pastures as "carbon sponges" will lead to all sorts of problems.

The real key is [to] adopt practices that enhance soil health to improve food productivity. This approach is much more likely to help in improve local livelihoods, protect water resources, improve biodiversity, reduce erosion and help put carbon back into the ground where it belongs.