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Assessing the status of drainage in UK agriculture: A case study in the demonstration test catchments - WQ0214

A well drained soil has long been recognised as being one of the most important beneficial factors in agriculture. As a consequence farmers have installed drainage schemes to reduce soil wetness since at least the 15th century with a rapid increase in the amount of land drained taking place from the mid 19th century onwards as technology provided better solutions. However, despite the importance of drainage many schemes were designed to follow local practice rather than being based on sound scientific principles taking account of soil and climate. This was especially the case in the period prior to the 1960s onwards. From the 1960s, led by the work at the Field Drainage Experimental Unit and driven by standards set as part of the MAFF capital grants scheme, drainage design standards improved and became gradually more unified. However, with the ending of capital grant schemes drainage activity on farms decreased dramatically and field observations suggest that maintenance of drainage systems has become a low priority on many farms. This may be a consequence of the fact that the older generation of farmers were relatively well versed in drainage techniques compared to the current generation many of whom will have little or no contact with grant aided drainage and the technical standards associated with it. Poor drainage has consequences for both the environment and agricultural production. Grassland will experience increased damage to the sward from poaching which may cause accelerated losses of particulate material and associated nutrients in surface run-off. On arable land poor drainage may result in increased surface runoff and cause significant erosive losses if it occurs at a time when crop cover is limited. Wet soils rapidly become anaerobic especially in autumn or spring when temperatures become elevated, this can cause substantial losses of nitrogen to the atmosphere as nitrous oxide which is an important greenhouse gas. Well drained soils also pose a threat to the environment as soil material mobilised on the surface due to rainfall impact passes through macropores reaching the drained rapidly providing a direct route to surface water bodies. This can cause increased transfers of sediment, phosphorus and pesticides to surface waters and a range of well-documented off-site impacts associated with the degradation of surface waters by multiple diffuse pollutants. The condition of the drains installed under farmland in England and Wales is therefore of considerable importance when considering diffuse pollution and pollution swapping issues. In particular the impact of poor drainage on denitrification and nitrous oxide losses is of considerable relevance to meeting the UK's obligations under international agreements.

This project aims to assess the current state of drainage in the UK via a set of case studies in the DTCs, gain an understanding of farmer appreciation of the role of drainage and at the same time review the quality of existing GIS data layers on soil drainage. The existing soil drainage layers were developed from statistics collected under the MAFF capital grant schemes and are a statistical representation of the likelihood of a given field being drained. Refined and more robust data layers would be of considerable advantage to those seeking to develop mitigation measures to minimise pollution and also would provide more robust modelling outputs. We will start by reviewing existing data layers and comparing our analyses with earlier work carried out at CEH using the same core data sets to identify if there are any inconsistencies. Data on the actual presence of field drains and maintenance activity will be collected by a combination of telephone surveys, and one to one farmer interviews using specialist drainage advisers. In addition we will undertake work to calculate the value of drainage to a range of services including both agricultural ones and to society in general. The potential to undertake soil drainage status/ drain condition surveys over a wider area by use of remote sensing techniques will be evaluated by undertaking a literature review.

The output of the project will be refined data layers describing soil drainage l and associated raw data to be provided to the DTC archives, a report to Defra identifying the policy implications of drainage deterioration covering diffuse pollution green house gases, flood risk and their relative values to society. We will also present the policy implications to Defra and other stakeholders and provide further briefings to rollout operationally important findings to farmers and others within the DTCs.

Project Documents
• ROAME Document : WQ01   (200k)
Time-Scale and Cost
From: 2010

To: 2012

Cost: £202,624
Contractor / Funded Organisations
Sustainable Farming and Food Science              
Water Quality              
Water Quality and Use