Sewage sludge success

15 January 1999

Sewage sludge success

At todays crop prices

alternative nutrient sources

can not be ignored. Sewage

sludge is one increasingly

popular option. Edward Long

visited a Notts farm which

has more experience of the

issue than most and is

reaping huge benefits

UNTIL 15 years ago a large part of the Severn Trent water companys Stoke Bardolph estate near Nottingham operated as a traditional sewage farm "cropped" with lagoons of sludge.

When these dried out the land was briefly reclaimed for agriculture before being needed again for lagoons. With poor soil structure and profuse weed growth yields of the occasional wheat crops were poor.

Now the estate, which still takes huge quantities of sludge, is run as a conventional farm and yields have rocketed.

Cropping on the free-draining sand and gravel river valley soil comprises 230ha (575 acres) of wheat and 130ha (325 acres) of winter rape, plus 100ha (250 acres) of grass and 170ha (425 acres) of forage maize for a 380-cow dairy herd.

"In the old days when lagoons dried out the land was cropped with grass for the cows and some wheat. But that was only opportunist farming," says farms manager, Chris Holt. "Wheat yields averaged just over 2t/acre and with an annual rainfall of just 22in the grass was also nothing special."

About 20 years ago it was realised that by adopting an integrated sludge recycling system there was scope to exploit the nutrient build-up in the soil.

At the heart of the switch was the development of an umbilical application system. That allowed accurate amounts to be put on, with treatments possible when soils would otherwise have been damaged. Digested sludge is now pumped through 20 miles of underground mains, 500,000cu m being applied annually.

The switch allowed a higher standard of farming to be implemented. Maize was the obvious first crop, needing a lot of nitrogen and allowing sludge to be applied all winter.

Most of the grass was ploughed up leaving only some along the river bank for heifers and 20ha (50 acres) around the dairy unit for lounging paddocks. The cows are now mostly kept inside and fed a winter diet all year round.

Last years maize yielded over 40t/ha. Sludge injection has had a good effect on soil structure and wheat yields have risen to 8.25t/ha (3.3t/acre).

"Yields like this on drought-prone land have been achieved without the need for artificial fertiliser," Mr Holt says. "This represents a saving of at least £50/acre on wheat which over nearly 600 acres adds up to a lot of money. We buy in just 15t of nitrogen to topdress crops growing alongside the river where we cannot use the organic material, so our fertiliser bill is almost nil."

The farm uses more sewage sludge than is normally applied to farmland. But the operation is well within legal limits and carefully monitored. Digested material, which has 2.5-3% dry solids, contains 2.5% N, 1.8% P, trace amounts of K and some sulphur. It is worth about £20,000 a year Mr Holt says.

As wheat is grown in a rotation with maize and rape about 70% of it is a first wheat for feed. But the legacy of years of heavy sludge use, high fertility conditions with top-end nutrient indices and organic matter levels of up to 10%, mean it has to be managed carefully if the value of the "free" nutrients and the crops full potential is to be exploited.

"Excessive tillering, a high risk of lodging, and heavy weed growth are the main problems we have to cope with every season," says assistant farms manager John Jackson. "We find the low tillering Consort suits our system. But no matter which variety is grown wheat must not be drilled early as this would encourage tillering, to increase the lodging risk, boost the chance of frost killing a winter proud crop, and increase disease pressure. We do not start drilling wheat until early October."

Seed-rate is based on thousand grain weight with the aim of establishing a final population of 200/sq m, which is about two-thirds the normal target for most wheat growers. This is equivalent to an initial established population of 250/sq m for a lightland crop, and 275 on heavier parts of the farm.

With a massive weed threat on the fertile land there is little scope for herbicide rate cutting. A mixture of diflufenican + IPU is sufficient to keep crops clean on 90% of the farm without a follow-up.

Where surviving broad-leaved weeds do pose a threat a dose of metsulfuron-methyl (Ally) is used, with fluroxypyr (Starane) applied where cleavers are troublesome. On the 10% of the farm infested with blackgrass, IPU + trifluralin (Autumn Kite) is used.

Some fields have above average levels of heavy metals, a result of sludge applications made decades ago, before controls were in place. But those are still within the UKs strict limits, Mr Holt notes.

Applications are not adding to the burden and recent studies have shown the biological activity of the soil has not been compromised. Earthworms are plentiful. &#42


&#8226 Home to UKs 6th largest sewage treatment plant.

&#8226 Waste treated from 0.5m people.

&#8226 1300cum of waste processed each day.

&#8226 0.5m cu m of sludge a year.

&#8226 20 miles of underground mains.

Minimal environmental impact is a key goal

After a five-year conversion period for the cropping attention turned to restoring the environment. "Historically much of the estate had suffered under the old management regime and was rather featureless. The new system provided an opportunity to put back the clock by restoring hedges and planting trees," says Chris Holt.

Since the early 1990s 10,000 trees have gone in, 10 miles of hedges have been replaced and three ponds dug. "Within five years the hedges took shape and we felt we should let local people in to see what we had achieved. We provided 15 miles of discretionary access and soon detected a positive response from visitors, wildlife groups, and local politicians," says Mr Holt. The estate now receives 50,000 visitors a year.

Temporary wetlands and other habits for insects, birds and mammals have also been incorporated into a wildlife plan. Conservation strips planted with sunflowers, kale, mustard and buckwheat are laid down each year to provide food and cover for birds and corners and strips left when harvesting maize.

"Our wildlife initiative is an integral part of the overall business and not a bolt-on sop to environmentalists. There is a big pay-off as the countryside in which we live and work is improved, and the public is more sympathetic to our farming methods. This initiative is now woven into our plans to meet the needs of crop assurance schemes," notes Mr Holt.

Keeping environmental impact to a minimum and improving habitat where possible is a key goal for Chris Holt. The policy is reaping benefits in terms of public acceptance.

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