Surface runoff ‘main source’ of phosphorus loss in arable fields

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The study, led by Scotland’s Rural College (SRUC), reviewed current knowledge of the transport mechanisms that release nitrogen and phosphorus into waterways.

Tramlines are the unvegetated rows found in many arable fields that over time can gradually become compacted. According to the researchers, it is a “major pathway for sediment and phosphorus transport via runoff erosion”.

Sediments are a key carrier for many harmful pollutants and contaminants such as nutrients, heavy metals and pesticides. They degrade water quality and also silt riverbeds, which are essential for the early life stages of many species, including salmon and trout, and various water fly life forms.

The study follows another report published in February which found that the level of agricultural pollution entering the aquatic environment increased significantly during the 2019/20 winter – one of the wettest on record. .

The report showed that nitrate levels in Devon’s River Taw quadrupled during the wet winter due to recently converted arable land, and sediment lost to grazed grassland roughly doubled, runoff from nitrates increasing by about half.

READ MORE: Is DEFRA ‘tinkering around the edges’ of agricultural pollution?

The SRUC study, which focused on Scotland, says surface runoff and erosion are “the main sources” of phosphorus loss in arable soils, and that standard farming practices are the main source of nutrient pollution rather than poor nutrient management practices in the country. .

Joanna Cloy, who led the research, said: “Improving water quality is important for society at large. However, the agriculture industry will also benefit from preventing the loss of valuable soil and nutrients from their land, as well as improving soil health.

The researchers reviewed the preventative measures and solutions available to minimize nutrient losses, as well as the associated costs and water quality impacts.

The report recommends that reducing agricultural traffic when the soil is close to field capacity, or particularly wet, would reduce the potential for compaction along tram lines and can be achieved by considering the timing of operations.

He adds that the use of “very flexible tires” on agricultural machinery or the disruption of tram lines with a spike harrow have been shown to “dramatically reduce the loss of sediment, nitrates and of Scottish soil phosphates under winter-sown combination crops”.

Reducing the source of nutrient loss using nutrient management plans is also promoted as an effective mitigation measure by researchers.

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