Arable News

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New guide plays role in stemming drainage investment decline

The basic principles of fielddrainage, as well as maintenance and installation information, are the subjectof a new practical guide issued by AHDB.

By refreshing knowledge on drainage,it is hoped that the guide will play an important role in stemming the declinein UK drainage investment.

Well-drained soils enhance theresilience of land by making it more able to withstand weather shocks such asthose seen in the wet autumn of 2012.

Fields have been drained foragricultural use for centuries but the last significant nationwide investmentoccurred in the wake of World War II, when grant aid and advice was freelyavailable as part of a productivity push.

Grant aid and free advice dried up inthe 1980s and the rate of installation of new drains has declined.

Good field drainage is of particularvalue to growers on heavy soils, in high rainfall areas or where the watertable needs to be controlled.

Guide co-author Kirk Hill, ADASSenior Soil and Water Engineer, said: In essence, good drainage is aboutmanaging soil to help it return to field capacity.

Soils in a well-drained state tendto work more easily and provide yield benefits.

This guide explains how to getfields in that state, which often does not involve a significant capitalinvestment. 


The guide describes how a relativelysmall investment, such as locating and maintaining existing ditches and drains,is likely to reap rewards relatively quickly.

Mr Hill said: If ditches becomeinfilled and outfalls are not kept clear, the field drainage system will ceaseto function effectively.

This can result in yield-robbingwaterlogging beneath the surface and is not merely a problem when there arevisible wet patches in the field.

To control drainage, the first thingto do is rummage around the farm office for drainage plans or create a new planshowing pipes, outfalls and ditches.

Once located, blocked outfalls canbe cleared with a spade in a matter of minutes and blocked drains cleared usinga rod or a jet to rejuvenate an entire field.

Useful guidance to help growerslocate outfalls, such as checking ditches after rainfall in autumn and winterwhen there is less vegetation, is detailed in the guide.


For growers considering installing anew system, the guide provides outline costs and real-life case studies.

Based on 2015 prices, it is estimatedthat a new system typically costs around 2,5003,500 per hectare for drainagewith permeable backfill and around 1,5002,500 per hectare for drainagewithout backfill.

Costs can vary greatly and growerslooking to invest in a new system are advised to seek the opinions ofexperienced land drainage consultants and contractors.

Not allabout drains

All drainage systems work best intandem with good soil structure, because if soil is compacted it impedes theflow of water to the pipes. In fact, maintaining good soil structure may evenavoid the need for capital investment.

The guide also features informationon subsoiling and topsoil loosening and details when it is appropriate tosupplement the drainage system with mole drains.


Mr Hill concluded: All landownersshould take drainage seriously and invest in their land, and the lack of grantaid should not be a disincentive, particularly for simple maintenance tasks.

It makes good business sense toinvest and the pay-back period for some of the less intensive managementoptions is rapid.

The good news is that the increaseduse of yield maps is helping to flag up poorer yielding areas in the field andmaking growers question whether it could be due to a hidden soil drainageissue.

The AHDB Field drainage guide can bedownloaded from

Copies can also be picked up from theAHDB stand at Tillage-Live on 16 September 2015.

  • Written by: Farmers Guide
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