What is happening to our soils?
The UN's Report Status of the World’s Soil Resources identified ten threats to soil functions.
- Soil erosion removes between 25 and 40 billion tonnes of topsoil every year. Annual crop losses as a result of soil erosion are projected to be over 10% by 2050, equivalent to removing 1.5 million km2 of land from crop production – or roughly all the arable land in India.
- Soil organic carbon (SOC) is the basis of soil fertility, releasing nutrients for plant growth. It promotes the structure and biological and physical health of soil. The conversion of forest to cropland results in losses in SOC stocks of up to 25-30%.
- Soil nutrient imbalance occurs when nutrient inputs are either insufficient to allow crops to achieve their development, or in excess of the nutrients exported during harvest. Nutrient excess is a major contributor to water quality deterioration and to GHG emissions (especially nitrous oxide). As a result of nutrient imbalances, 66% of all nitrogen reaching the Gulf of Mexico comes from the production of crops within the basin.
- Soil acidification is the lowering of soil pH due to the build up of hydrogen and aluminium ions, and the loss of base cations such as calcium, magnesium, potassium and sodium due to leaching or product removal. Over 25% of soils in Africa are acidic and in South Africa soil acidity is cited as the greatest production-limiting factor.
- Soil contamination is the addition to soil of chemicals or materials that have a significant adverse effect on any organism or on soil functions. In China, nearly 20 million ha of farmland (approx. one fifth of China’s total farmland) is contaminated by heavy metals.
- Soil water-logging is when the soil is too wet, resulting in insufficient oxygen in the pore space for plant roots to be able to respire adequately. In Pakistan water-logging affects between 1.6 and 3.7 million ha.
- Soil compaction is the increase in density and a decline of macro-porosity in a soil that results from pressure being applied at the soil surface. Soil compaction is a major contributor to floods. In some parts of Britain, soil compaction has increased the rate of instant run-off from 2% of all the rain to 60%. Nearly 33 million ha is compacted in Europe, 18 million ha in Africa and 10 million ha in Asia, due to machinery, cattle trampling and insufficient cover of the top soil by natural vegetation or crops.
- Soil sealing is the permanent covering of an area of land and its soil by impermeable artificial material, for example through buildings and roads. This trend is accelerating, with the world’s urban population projected to rise from 54% to 66% (of the total population) by 2050.
- Soil salinisation is the accumulation of salts in the soil, exacerbated by irrigation e.g. with salt-rich irrigation water and/or insufficient drainage. 20 million ha in India, 7 million ha in China, 5.2 million ha in United States and 2 million ha in Pakistan are affected by soil salinity.
- Soil biodiversity loss is a decline in the diversity of micro- and macro-organisms present in the soil, critical for soil formation, nutrient cycling, regulation of carbon and water. 56% of soils within the EU have some degree of threat to soil biodiversity.
What does this matter... what do soils do?
Put simply, soil is the source of all life. It is critical to …
- Our food. Soils are the foundation of food production, supplying plants with nutrients, water, and support for their roots. 95% of our food is directly or indirectly produced on our soils.
- Our water. Soils function as Earth’s largest water filter and storage tank. They also play a key role in resilience to floods and droughts.
- Our growth. Humans and animals acquire the nitrogen needed to make amino acids, the building blocks of proteins, from plants and ultimately from the soil.
- Our climate. Soils store more carbon than is contained in all above- ground vegetation and help regulate COemissions and climate processes.
Given these critical life supporting functions, next week we discuss ‘Soil and climate change’, before concluding with ‘Soils’ role in ensuring food security’.