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Land Erosion
Land Erosion
UK
UK
Intensive agriculture has already caused arable soils to lose 40% to 60% of their organic carbon. Soil erosion in England and Wales is lower than many other countries, but it is estimated by the government that 2 million hectares are still at risk. Around 3.9 million hectares are at risk of soil compaction in England and Wales – nearly twice the total area of Wales. The highest UK erosion rate found was more than 140 tonnes/hectare per year – recorded on a single field in West Sussex in the early 1990s.
The Climate Change Committee’s Soil Case Study says " Erosion in England and Wales was calculated to be approximately 2.9 Mt yr-1, which is similar to the 2.2 Mt yr-1 estimate given by the Environment Agency (EA).” The majority of this erosion was associated with silts and sands, especially on arable and horticultural land, where mean per hectare erosion rates were also highest.
There are fields - sandy ones- in Britain losing 47 tons of soil per acre per annum. Do remember, when looking at the soil biome, we found the weight of soil is about 1.5ton m3, so that equates to about 30m3 washed away. Using the same biome figures, that means the loss of 40million kilograms of worms and about the same amount of small arthropods. With the loss of other creatures that must be getting on for 100mkg of soil fauna being washed away.
In UK it has been calculated that soil degradation is costing well over a £1.2billion a year. “mainly linked to loss of organic content of soils (47% of total cost), compaction (39%) and erosion (12%). Eighty percent of costs occur off-site and, as such, are often of limited concern to those whose actions may be causing soil degradation” (Graves et al 2015). As Natural England notes, “soil and nutrients washing off agricultural land is the most common reason for our rivers and streams becoming unhealthy”.
Low erosion is due to a mixture of factors, particularly climatic conditions. The temperate maritime climate, with relatively mild temperatures and moderate rainfall provides a generally moist environment which encourages vegetation growth. This in turn helps stabilise soil, by protecting it from heavy rain, thus reducing erosion. The topography, of gentle slopes - the ‘rolling countryside’ means that runoff is less forceful
According to government estimates about 20 years ago, 2.2 million tons of soil were being lost each year, now they are nearer 3m. There was a round-up of the impacts of erosion on arable in 2013 (Boardman 2013)
There are five main grade of land – Grade 1 is very good and can grow a couple of crops a year, Grade 2 is somewhat less flexible but still grows grain, Grade 3 is ideal for pasture and mixed farming, while grade 4 is less adaptable, and Grade 5 really rough grazing. In the UK we are loosing about 1 mill tonnes of poor soil from the mountains and moors in the West, and 2 million from our best grade 1&2 soils in the East.
"Whilst mean erosion rates in the UK are low, relative to the rest of Europe for example, 16% of observations on arable land were greater than the supposedly tolerable rate of 1 t ha−1 yr−1 and maximum erosion rates were as high as 91.7 t ha−1 yr−1. " (Benaud et al 2020).
Dashboard of interactive factors determining soil degradation in EU (but excluding UK thanks to Brexit)
Europe
The mean soil loss rate in European Union is estimated to 2.46 t/ha annually, with over 12% loosing 5tons in Europe (Panagos et al 2015).
A staggering 61% of EU soils are in an unhealthy state with around 1/3 of that due to erosion by water (loss of soil organic carbon 48%, and the loss of soil biodiversity (37.5%).
“Thresholds have been set for each soil degradation process to categorise healthy from unhealthy soils. These thresholds have been based on a combination of scientific estimates and adopted critical limits. They represent an estimate of the point beyond which most soils can reasonably be considered unhealthy or vulnerable to a certain process”. Grey on the map equals concrete, while deep red the maximum number of concurrent ‘degradations.’
World
Soil erosion globally has resulted in around 25 to 40 billion (or giga) tons of increased sediment every year from cropland, according to remote sensing. “Most cropland soils, whether rain-fed or irrigated, have lost much of their organic matter and soil life, resulting in more rapid soil erosion than at any time in history — about 21 gigatons per year on croplands alone."
When we talk about tons lost, we are measuring the silt/sediment, rather than life. Most of the weight - 95% is mineral - and would account for most of the sediment. But the remaining 5% would be ‘life’, which weighs in at over one billion tons. That would be the worms, springtails mites as well as the fungi and bacteria which make up soil life. Translated into human beings that would be well over three times the present human population - which is estimated to weigh over 300m tons.
Biodiversity
Biodiversity
Throughout this site we have been looking at the soil biome - the breadth of organisms from bacteria, algae, fungi plant roots, small arthropods, nematodes and worms. There have been times when they have been affected - most notably after the great End Permian Extinction 250mya. Now however, losses are due to our farming techniques and concretisation Farming now includes ploughing, plantations and monocrops, and many more chemicals. Nowadays the main impacts include:
Soil degradation: Modern farming practices such as intensive tillage, heavy use of chemical fertilizers, and monoculture crops can lead to reducing the diversity of soil organisms and their functions.
Loss of soil organic matter: The heavy use of chemicals, like fertilisers and pesticides can lead to a reduction in soil organic matter, which is an essential component for maintaining soil health and biodiversity.
Changes in soil structure: Intensive tillage can damage soil structure, reducing soil biodiversity by disrupting the physical environment that supports microorganisms and invertebrates.
Soil compaction: Heavy machinery and livestock can compact the soil, reducing the infiltration of water and air into the soil, which can negatively affect soil biodiversity.
Loss of habitat: The conversion of natural habitats, such as grasslands and forests, into agricultural land can lead to the loss of biodiversity, including soil biodiversity.
Reduction in crop diversity: Monoculture farming practices, where only one crop is grown, can lead to a reduction in soil biodiversity by limiting the diversity of nutrients and habitat available to soil organisms.
The United Nations sees biodiversity as our 'strongest natural defence against climate change', but doesn't mention soil biodiversity. Luckily, the European Environment Agency says: "Restoring ecosystems would also support biodiversity and enhance a wide range of ecosystem services.... improving soil quality could be a very cost-efficient measure in terms of climate action with a triple impact. First, growing plants remove carbon dioxide from the atmosphere. According to the FAO, restoring currently degraded soils could remove up to 63 billion tonnes of carbon, which would offset a small but important share of global greenhouse gas emissions. Second, healthy soils keep the carbon underground. Third, many natural and semi-natural areas act as powerful defences against the impacts of climate change.
Compaction
Compaction
According to government figures in England almost 4 million hectares of soil are at risk of compaction. he main cause of soil compaction is the weight of machinery, which has increased dramatically over recent decades. Other factors include high tire inflation pressures, wheel slip, and the number of passes a vehicle makes over the soil. On fields cut for silage, there may be four/five passes a year for cutting, and a further 2/3 for slurry distribution. Compacted soil can affect soil fertility, increase the risk of flooding, reduced capacity to store rainfall, which can lead to more rapid overland flow and erosion and can restrict root growth. It must also affect aeration
”Only one in eight fields has high earthworm numbers..and Almost 4 million hectares of soil are at risk of compaction in England and Wales, affecting soil fertility and our water resources, and increasing the risk of flooding"
The weight of these machines is comparable with dinosaurs. The soil survived dinosaurs, perhaps because they came by only now and then. "The similarity in mass and contact area between modern farm vehicles and sauropods raises the question: What was the mechanical impact of these prehistoric animals on land productivity? (Keller & Or 2022) ) Farm vehicles have grown over the past few decades, to the point where they may be compacting the subsurface soil where roots of crops extend.
Today, that average weight (of a combine harvester) has grown to over 35,000 kg. To avoid crushing the soil beneath this bulk, tyres have got larger, and they're operated at lower pressures, allowing the tyre to spread over a larger area to limit the compaction of the surface soil. The stresses (that go deeper down) largely depend on the mass per wheel. The difference with dinosaurs is that, while they may have passed by occaisionally, these machines may go over the same land 6-8 times a year.
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