BIOBEDS LOOK set to become common features on many conventional arable farms, as water companies and the Environment Agency home in on the costly problem of pesticide contamination.

 Much more attention needs paying to in-yard operations, according to recently retired ADAS mechanisation officer Bill Basford.

 At least 40% of pesticides reaching water do so through so-called point source contamination caused during filling and washing down sprayers. Mr Basford estimates the figure could be 75% in some areas.

Too often drained concrete yards allow accumulated pesticide drips, splashes and spills to be washed into watercourses. Containment and treatment must be the answer, he believes.

“Most people, when you talk to them, realise they could do something to improve their practices.”

 The proven way to go about it is to install a biobed, and exemptions under impending waste management laws look set to make that easier, he suggests.

Not only will it guard against accidental pollution of watercourses, it could avoid having to pay for groundwater authorisations for existing waste disposal facilities.

 For three years, Mr Basford has been testing three biobed designs on a Lincs farm. All have absorbed and degraded nearly all the pesticide fed into them.

 “We”ve found we can reduce the concentration of the ingoing solution by up to 100,000-fold. It”s really exciting stuff.”

Detailed monitoring and sampling in the DEFRA/EA-funded work explored the fate of six commonly used pesticides (see box) through the lined organic degrading pits.

“The proof of the pudding is that 87% of the samples coming out of the biobeds were below a concentration of 0.5g/litre and often under 0.1g/litre.” The figures respectively are the maximum limits for total pesticides and a single pesticide under EU drinking water regulations.

“The key point is the EA is now saying that if a farm has a biobed and re-uses the liquid that comes out of the bottom, then it won”t need a groundwater authorisation.”

That could rule out having to pay over 100 for registration and a similar annual fee, he explains.

 andrew.blake@rbi.co.uk

Getting it right from the start

 WORK WITH experimental biobeds has pinpointed practical tips to bear in mind when installing and operating them, says Mr Basford.

 Dig the pit, with gently sloping sides, at least 1m (3.3ft) deep. Line it with impermeable material such as plastic sheet. Use sand backing to avoid punctures.

Beware underground obstructions, such as electricity cables.

Allow about 1sq m of biobed surface area for every 1000 litres to be treated each year.

 Install a drain to feed treated water into holding tank.

Make the offset pad (with 100mm bund) or drive-over area big enough to accommodate the sprayer – and tractor if involved – and allow room for the operator to work around it when filling and washing down.

Install a silt trap in the drain from the concrete pad to protect the pump.

Fit float switches to control pumping from the holding sump for an offset biobed and from discharge tanks to irrigation systems.

 Use a rigid hose network for distribution over offset biobeds and waste ground. Rodents eat through trickle irrigation tape.

 Minimise rainwater entering the system, if necessary by roofing and/or installing drainage channels.

Ensure turfs used for topping off have at least 5cm (2in) of soil to ensure proper grass establishment. The EA suggests that biobed contents should be removed after 5-7 years and disposed of through composting under cover for a further year.

Lincs Farm leads the way

BIOBEDS” POTENTIAL has been highlighted in three versions (see panel) at R&R Farms, Stainton by Langworth, Lincs.

The basic design, first used in Sweden where many farms now employ biobeds, is a lined pit at least 1m deep filled with an organic mixture containing micro-organisms which break down pesticides. At the bottom is a drain, preventing overflow during heavy rain, whose discharge is trickle-irrigated over small areas of land.

Laboratory experiments at HRI Wellesbourne found that a turfed mixture of 50% straw, 25% peat-free compost and 25% soil worked well in filtering out and breaking down pesticides, and the Lincs field work at two sites confirms this. Any concern that low temperatures might reduce biobeds” effectiveness has been dispelled.

 “I”m comfortable that they work as well in winter as they do in summer,” says Mr Basford.

Another possible option, as at one R&R site, is to employ soil alone as the degrading agent. Two years”