Fen Management Handbook - Scottish Natural Heritage

8.2 Managing the source of nutrient enrichment
The majority of fens receive a proportion of their water supply from the surrounding
catchment, either as surface run-off or groundwater recharge. This water can
become charged with nutrients from various sources, including point-sources such
as leachate from farmyards, septic tanks etc., and more diffuse sources such as
fertiliser. Legislation and guidance which seek to limit nutrient-enriching farming
techniques are endorsed by financial incentives available through Environmental
Stewardship and similar schemes which encourage farmers to reduce nutrient use
and pollution. Nutrient enrichment from the surrounding catchment nevertheless
remains a problem for many fens, beyond the direct influence of many fen
managers.
Catchment management aims to address nutrient enrichment at source, by
producing a strategy which addresses all diffuse and point sources of enrichment
within a catchment area. Some agri-environment support measures include a
premium to encourage a high proportion of farm holdings within a catchment to
become involved in this kind of initiative (see Section 12: Economic Aspects of
Fens).
8.2.1 Crop and soil management
Various projects around the UK, including WWF’s Wild Rivers project and West
Country Rivers Trust’s Tamar 2000 project, have demonstrated the capacity to
achieve significant reductions in nutrient enrichment from artificial fertiliser and
farmyard manure by providing free nutrient budget service and/or offers of free
soil testing which encourage more targeted fertiliser application to optimise plant
uptake and avoid leaching of excess nutrients. Other initiatives to target agricultural
fertiliser application include computer models such as MANNER for nitrogen
management and PLANET for phosphorus, both available on the Defra website.
More general guidance for farmers and land managers which can help with
catchment management includes:
– spring is considered the optimal time for application of N;
– cultivation in autumn should be avoided, as it releases greater levels of N;
– fertilisers should not be applied to wet ground or during periods of heavy rain;
– fallow periods and reduced cultivation allow soils to regain good crumb
structure;
– contour tillage reduces runoff;
– maintaining over-winter ground cover helps prevent soil loss from erosion.
Basic recommendations for manure application include:
– cultivate soon after slurry applications to encourage uptake of nutrients;
– autumn and spring applications result in higher levels of diffuse pollution;
– N loss is greatest in free-draining soils in the autumn;
– P losses are greatest when soils are wet, typically November and December;
– composting manure before application can inactivate pathogens, increase
ammonia release and tends to remove P and N.
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