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Soil erosion has been recognised as one of the major threats to the sustainable use of soil and land resources in Europe. Although soil erosion is a natural phenomenon (where soil losses are in balance with soil formation rates), human intervention in the form of land management can accelerate soil erosion rates beyond soil renewal rates, so that a net loss of soil occurs.
 Loss of soil by erosion results in declines in soil depth, preferential removal of nutrients, organic matter, agro-chemicals, seeds and trace elements, and a reduced soil microbial population. These losses can reduce soil fertility and productivity, so that yields decline and there is less protective vegetation cover and root mass to protect against erosion processes in subsequent years. This sets up a viscious circle of “erosion – loss of topsoil – poor vegetative biomass – erosion” which is unsustainable in the long term. Indirect consequences of soil erosion include damage to emerging plants, exposure of less fertile sub-soil, and a reduction in water holding capacity. Once eroded, the sediments enter water courses leading to increased turbidity, pollution from the sediments and any contaminants adsorbed onto them, changes in water temperature, light penetration and available oxygen, and deposition of sediment. All of these factors can have detrimental effects on aquatic flora and fauna. Many studies have shown the sensitivity of aquatic ecosystems to even low levels of water pollution by sediment and its associated contaminants.
SOWAP aims to address some of these issues on arable land in northern and central Europe, where erosion rates have been a concern for many years. Here, land preparation and crop agronomy requires many field operations, especially for winter cereals in the UK and sugar beet in Belgium. These operations include seedbed preparation, where numerous tillage operations are required to break up the soil tilth to ensure good contact between drilled seeds and soil media. Whilst in the short term, soil surface roughness levels are high, encouraging surface ponding of water, this roughness is lost as aggregates slake and breakdown when subjected to raindrop impact after one or two rainfall events, giving high soil losses.
 The collapsed soil structure can result in redistribution of dislodged fines to create surface seals and caps that have negative impacts on seedling emergence, reduce infiltration and thus encourage surface runoff, often with high sediment concentrations. Repeated trafficking and wheelings from numerous field operations increase bulk density and reduce porosity; two factors detrimental to control of runoff. When combined with reduced topsoil depth, soil productivity and crop yield may decline.
In the light of these negative impacts, a more conservation oriented land-use system will be beneficial in protecting soil resources and maintaining surface water quality. Much is known about the principles behind soil conservation practices. However, there is a considerable gap between what is known in principle and what is applied in practice. SOWAP aims to provide evidence to overcome the constraints to adoption and implementation of soil and water conservation strategies by demonstrating practical and realistic erosion control solutions, concentrating on the use of conservation tillage.
In principle, the objective of conservation tillage is to “maintain a fertile seedbed in the soil, whilst retaining maximum resistance to erosion”. The aim is to:
- Create a good environment for growing crops
- Optimise soil and water conservation
- Maintain sound economic practices (no decline, preferably an increase, in yield as a result of practices)
- Use maximum or optimum retention of residues from previous crop
- Use herbicides to control weeds, where tillage would be used conventionally
- Control soil and water losses by
 % cover (residues and crop canopy)
maintaining surface roughness (residues, soil surface structure and crop stem density)
simulate root effects (by crop and any incorporated residues).
With these principles in mind, SOWAP aims to demonstrate:
- the environmental impacts associated with “conventional” arable land use practices.
- the viability and effectiveness of “conservation oriented” arable land management systems in protecting soil resources, improving catchment water quality and promoting biodiversity.
Please follow the links below to find out more about the problem of soil erosion (Summary) and the Objectives of this part of the project. |
