3.1.5 Soil degradation
** REferences to update**
3.1.5 Soil degradation
"Soil is lost rapidly but replaced over millennia and thisrepresents one of the greatest global threats for agriculture" Duncan Cameron, Professor of Plant and Soil Biology at the University of Sheffield
Increased deforestation, overgrazing and the use of chemicals are also causing severe damage to our soils. This process is exacerbated by increases in extreme weather events, such as extreme rainfall that causes fertile topsoil to be washed away into rivers, or increased erosion due to drought, winds, or high temperatures.
Indeed, erosion carries away 25 to 40 billion tonnes of fertile topsoil every year and a third of our soils are now classified as being moderately or highly degraded. It can take about 500 years to form just 2.5 cm of topsoil, yet we are currently losing soil 10-100 times faster than it can be regenerated. This problem is made worse by the fact that earthworms - creatures that usually play a key role in the restoration of degraded soils - cannot compensate for the loss of healthy soil as they too have been depleted by 80% or more by the chemicals used in intensive farming. The UK has some of the most degraded soils on Earth, with nearly 85% of fertile peat topsoil in East Anglia having been lost since 1850, and the remainder at risk of being lost over the next 30-60 years.
A whopping 95% of what we eat relies on healthy soils, so degradation of our soils is having a huge impact on global food production - see section on human impacts on global food production.
Loss of topsoil also leads to increased pollution, flooding and desertification.
Soil degradation also has a knock-on effect on global warming. Soils hold around 70% of the planet’s land-based carbon, mostly from dead plant or animal matter, which is processed and cycled by small animals and microorganisms, such as earthworms, bacteria and fungi. In fact, just a spoonful of healthy soil contains 6 billion microorganisms. However, when soil is repeatedly ploughed or compacted by heavy machinery or livestock, the ability of the soil’s biological communities to store carbon is compromised and vast quantities are released back into the atmosphere in the form of carbon dioxide. (See section on intensive agriculture).
Globally, it is estimated that agricultural soils have now lost up to 75% of the carbon they held before being used for agriculture - or maybe more.