Cover crops reduce nutrient losses and leaching

It is important to take steps to reduce the risk of nutrients being washed off fields.

High levels of nutrients in water bodies can cause algal growth and ‘choking’ of aquatic life.

What is nutrient leaching?

Nitrate (a form of nitrogen) is not strongly attracted to soil particles and can be washed away (leached) in solution.

Phosphate, which is attached to soil particles, can also be lost in soil run-off after heavy rainfall.

Losses are more likely to occur in autumn and winter when soil moisture and rainfall levels are high, especially when soil is left bare.

How cover crops reduce nitrate leaching

Cover crops take up nitrogen and help reduce nitrate leaching.

Nitrogen uptake by cover crops sown in late summer/autumn ranges from 30 to 120 kg N/ha before the spring.

Cover crops also bind the soil and provide canopy cover, helping to reduce phosphate run-off.

The amount of nitrogen uptake depends on the species used, drilling date and success of establishment.

Species choice

• Non-legume crops are best
• The most effective species are brassicas, cereals and phacelia (if sown early)
• Deep-rooting crops, such as fodder radish, plantain and stubble turnips, may reduce nitrogen leaching into watercourses by as much as 40%

Drilling date

• Earlier-drilled (late August) cover crops are more effective at reducing leaching than those drilled later (late September)
• Later cultivations could stimulate the mineralisation of nitrogen that is not captured by a cover crop, especially if it struggles to grow under cold conditions

Establishment

• Rapid early growth and root development are essential
• Lowest nitrate losses occur on fields with good ground cover

Further information

The ADAS Farmscoper model helps predict the impact of autumn-sown cover crops on nitrate, phosphorus, and sediment losses.