ARCHIVE: Fertiliser Manual (RB209)
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Protecting the Environment


Losses of nutrients from agricultural land can pollute both ground and surface waters and the atmosphere. It is important that farmers do everything possible to minimise the risk of agricultural practices causing environmental pollution.

Some areas of agricultural land are subject to various types of agreement for maintenance or improvement of the environment and farmers may have to comply with restrictions on the use of fertilisers and manures. Farmers in these areas may need to modify the recommendations in this Manual in order to comply with specific requirements.

There is guidance in Protecting Our Water, Soil and Air: A Code of Good Agricultural Practice and in the NVZ Guidance Leaflets (Section 9). Environmental issues are described in Section 1. There are some issues particularly associated with grassland due to common conditions (sloping land, high rainfall, soils relatively high in organic matter) and to the presence of manures, either applied or deposited by grazing animals.

Nitrate

  • Farmers of land within NVZs have to comply with mandatory rules which aim to reduce nitrate movement to water. These rules are set out in NVZ Guidance Leaflets (Section 9).
  • Movement of nitrate to water can be reduced by careful matching of rate and timing of fertiliser nitrogen applications to the needs of the crop. Account must be taken of nitrogen supplied by the soil, previous crop residues and organic manures.
  • Other measures which will reduce the risk of nitrate pollution include:
    • applying organic manures and fertilisers close to the time when the nitrogen is needed for crop growth.
    • avoiding autumn and early winter application of manures wherever practically possible.
    • reducing fertiliser nitrogen use where grass growth is restricted by summer drought.

Ammonia

  • Ammonia deposition is damaging to the environment due to its contribution to acid rain and excessive enrichment of nutrient-poor habitats.
  • Livestock manures are the largest source of ammonia with greatest losses from housing and spreading to land.
  • Ammonia emissions can be reduced by incorporating manures after spreading (where possible) and by applying slurry with a band spreader or injector.
  • Reducing ammonia loss from late winter and spring applications of manure will also conserve available nitrogen for crop uptake.

Phosphorus

  • Phosphorus can be damaging to water quality in rivers and lakes where it may cause excessive algal or weed growth.
  • Phosphorus is lost from grassland mainly in surface run-off from recently spread manures, soil erosion, or dissolution of readily-available soil P, and in drain outflows in soluble forms or attached to soil particles.
  • The risk of phosphorus loss can be reduced by:
    • taking full account of the phosphate content of organic manures when deciding on fertiliser requirements.
    • following the recommendations in this Manual to avoid increasing soil P Indices beyond those necessary for crop production.
    • avoiding surface applications of manure when ground conditions are unsuitable or on steeply sloping land adjacent to water courses
    • reducing reliance on imported concentrates

Nitrous oxide

  • Nitrous oxide, a powerful greenhouse gas, is formed during denitrification of nitrate-N and nitrification of ammonium-N in the soil.
  • The amount emitted is related to concentrations of ammonium-N and of nitrate-N which can be restricted by matching nitrogen inputs to grass demand.
  • Using recommendations in this Manual and, in particular, making effective use of nitrogen in organic manures will help minimise emission.
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