29 March 2002

How biosolid improved soil structure and yield

Interested in using sewage sludge to boost soil

structure and crop performance? The latest results from a

Southern Water demonstration farm show just what

can be achieved. Brian Lovelidge reports

REGULAR dressings of digested sewage products over the past five years have significantly improved soil structure and crop gross margins on Southern Waters 66ha (164 acre) Bestway Farm on Weald clay near Horsham, West Sussex.

The average 7% gross margin increase for crops on regularly treated land is mainly thanks to higher crop yields and better grain quality, reckons Bill Griffiths, who runs Southern Waters sewage product sales and application operations.

The biosolids slow release of nitrogen, provision of minor and trace elements and promotion of much greater microbial activity in the soil explain the uplifts.

"Crops appear to be healthier with significantly less take-all in wheat and less mildew in all cereals, although not to the point where we can omit a fungicide spray," he says. "But we have been able to save a spray against pea and bean weevil on peas. We usually see a few leaf notches and then the pest disappears."

Eight of the farms nine fields are down to a four-course rotation of wheat, wheat, oats and a spring break of peas, oilseed rape, grain maize or barley. The ninth field grows continuous wheat.

The two sewage products, 25% dry matter digested cake or 92% dry matter granules, are applied at around 25t/ha and 2.5t/ha respectively every two or three years, mostly to half fields for comparison. A control field receives standard inorganic N, P and K.

Improved soil structure was clearly demonstrated in February 2000 when, despite the sodden land, Mr Griffiths was keen to plough and drill continuous wheat. "The contractor said he wouldnt be able to plough, because it was so wet, but he was surprised to find it was possible and Claire was drilled into a reasonable seed-bed on Feb 24.

"The contractor tells us that the treated fields get easier to plough every year. The job is done half a gear quicker than five years ago. The improved soil structure means seed-beds are also generally better."

Better crop establishment and tillering has resulted, allowing seed rates to be cut by about 30%. Apart from one late-drilled field all the wheat went in between Sept 25 and Oct 5 at 185kg/ha last autumn.

Initially Mr Griffiths cut the bagged N rate in line with the amount of nitrogen supplied by the biosolids. But once it became clear that treated crops stood better, higher total rates were pursued. Wheat used to receive 190kgN/ha. Last years Claire continuous wheat had 220kgN/ha as bagged N, plus about 30kgN/ha from 25t/ha of biosolids. The crop received only a cheap, early PGR and did not lodge.

"Apart from last season weve been hitting 10t/ha of wheat. It has never lodged, so I think we can boost yield further with even higher bag nitrogen dressings without the crop going down, while still complying with the nitrate directive."

Mr Griffiths says 25t of digested cake contains about 250kg of nitrogen, available over several years, plus P and S. &#42

Apply any time

Application timings for digested sewage products will be unaffected by the EC nitrate directive, thanks to their low available nitrogen status, claims Bill Griffiths. "There will be no closed period for applying our products, unlike pig and chicken manures, cattle slurry and liquid biosolids. They are among the few nitrogenous fertilisers that can be used in the autumn across all soil types."

Certification guarantees standards met

Growers using Southern Waters biosolid products will now receive certificates guaranteeing they meet stringent quality standards and application criteria and, therefore, comply with quality assurance scheme requirements.

"With our certification farmers will be able to see what SW products have been used, where they came from, when they were made, the quality checks they have undergone and the products analysis," says Bill Griffiths, who runs Southern Waters sewage product sales and application operations.

SW supplies three products under its Bestway brand: digested cake, lime-stabilised cake and granules. A high K product containing ash from the new straw-burning power station at Ely, Cambs, will be launched this autumn.

Usual application rate for the digested and lime-stabilised cakes is 25t/ha and for the latter this dressing had a neutralising value equivalent to 3.3t/ha of agricultural lime. Application rate of the granules, is 2.5-3.5t/ha. Delivered, and spread with low ground pressure machines, the cake products cost £1.50-£2.50/t and the granules £14-£18/t.