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Field Drainage

Maintaining an efficient field and farm drainage systems ensures periods of heavy rain do not damage crops or grazing land and that excessive surface water is quickly drained away.

How can I create efficient drainage on my farm?

Review the current situation

  • Examine the current field drainage system on the farm
  • Consider field drainage requirements, the maintenance requirements, the amount of waterlogged areas, pollution, and the quality of water flooding through holding and habitats.

Identify potential opportunities for improvements to field drainage system

  • Identify poorly drained marginal areas
  • Create / improve specific wetlands to add value

Calculate the cost benefits of these opportunities

  • Consider the benefits of improved field drainage and better crop growth versus the costs of undertaking work, maintenance, soil erosion and pollution

Prioritise fields

  • Wetlands and areas adjacent to watercourses are important as buffer zones
  • Be aware of pathways that field drains and ditches follow to avoid rapid runoff of pollutants (nutrients and pesticides)

Develop an action plan for improvements to field drainage system

  • Review field drainage systems and identify need for improvement on a field by field basis using a farm map
  • Plan new field drainage for when drainage is inadequate but is required for timely and productive crop growth or reduce potential for soil damage by livestock poaching
  • Maintain existing field drainage.  Maintain land drains outfalls regularly. Make sure field drains stop short of watercourses to buffer them from soil and nutrient inputs
  • Sacrifice field drainage where the benefits of improvements (e.g. to allow for crop growth) are outweighed by the costs. Suitable areas may include land adjacent to watercourses, natural wetlands and ribbon areas at the base of steep slopes. These can be managed as buffer zones as wetlands and to provide summer “bite”
  • Consider creating small ponds and wetland areas at ditch junctions or by drainage outlets to help manage runoff and increase wildlife diversity
  • Avoid nutrient losses and the risk of watercourse pollution.  Do not spread fertilisers, manures, slurries and dirty water and liquid wastes such as dilute pesticides onto land that is well drained or has shallow drains in wet conditions

Check fields for signs of brown water runoff or sewage fungus, particularly during or after rain.

How are fields drained?

Historically drainage of fields has involved the strategic digging of a series of trench systems which help to divert the excess water away from the field.  Another method of agricultural field drainage is tile drainage. This involves replacing the trench system with buried lines of clay pipes or tiles. The system works by allowing surrounding excess moisture in the soil to drain our of the land and enter into the tile field drainage system. Water flowing within the field drains will ultimately be deposited into an exit point such as a river / stream / lake.

What are the benefits of a good drainage system?

Good management of field drainage systems can save you money and protect the environment.

The biggest benefit associated with lowering soil water content through drainage comes from the resulting changes in the crop rooting environment, which are beneficial to crop and soil management.

Other benefits include:

Soil workability and trafficability

  • A reduction in water content increases soil strength. In grazing systems, benefits will come from the increased number of days that livestock can graze without risk of damage to the soil. In crop conditions, the reduced water content of the topsoil allows increasing opportunities for cultivations during autumn / spring.

Increased soil temperature

  • Drainage reduces soil specific heat capacity and can therefore lead to increased soil temperature.

Efficiency of fertiliser use

  • Aerobic, warmer soil conditions will lead to a more efficient use of applied fertilisers, particularly N top dressings. Roots will absorb nutrients more readily and less will be lost by leaching or denitrification.

Yield advantages

  • Improved drainage can make the difference between crop success and failure in wet years. Yield advantages can range from 10-25% compared to un-drained soils.

Improved utilisation and composition of sward

  • In wetter regions, drainage is essential to help maximise utilisation of grass by livestock. The composition of the sward can be altered with grass of drained soil having less weed species, less bare ground and an increased response to N.

 

Adapted from the Rivers Trust Pinpoint Best Practice information sheet 20.0 Field Drainage.

 

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