7 April 2000

Adding manure to crops

– its all in the timing

By Bob Davies

APPLYING manures and sludges to arable crops between tillering and stem extension could boost crop performance and cut costs, say backers of a new LINK collaborative research programme.

Nine agencies and companies are involved in the joint MAFF/industry funded study, which aims to help farmers use nitrogen from organic manures more efficiently.

"Total NPK fertiliser savings of over £50/ha can be achieved if we exploit the nutrient and organic matter of manures and stop regarding them as storage and disposal problems," says Mark Shepherd, principle research scientists at ADAS Gleadthorpe, Notts and project co-ordinator.

First year results show how much nitrogen is available from liquid sludges and slurries applied in the spring compared with autumn-applied solid manures and sludges.

For standard dressings of 50cu m/ha the former supplied up to 125kgN/ha (100 units/acre) whereas the latter gave about 15kgN/ha (12 units/acre). "That is because most of the N in FYM and sludge cake is in an organic, slow release form," explains Dr Shepherd. However, later nitrogen release could be important and is being monitored.

Although little of the total nitrogen in the autumn applied solid manures was leached in an average winter, as much as 25% of the nitrogen in cattle and pig slurries and liquid sludge was lost, because it is a more readily available form. "Liquid manures have to be managed differently, because of this large amount of available N that is at risk of loss."

Switching to spring spreading could therefore be far more beneficial for the liquids. Results from early plot trials suggest about 40% of the 3kg N/cu m in cattle slurry is available to replace fertiliser, Dr Shepherd reports. That is equivalent to 60kg N/ha (48 units/acre) from a 50cu m/ha dressing.

With pig slurry 50% of the 5kgN/cub m of nitrogen content was used by the crop in year 1, equivalent to 125kgN/ha (100 units/acre). Liquid digested sludge applied in the spring contained 2kgN/cu m with 35% used by the crop, equivalent to 35kgN/ha (28 units/acre).

For autumn-applied dewatered sludge cake 7% of the 9kg/cu m of the total N content was found to be accessible in the first year. For a typical application rate of 50t/ha that is equivalent to 30kg N/ha (24 units/acre). Autumn-applied, well-rotted cattle manure contained 6kg N/t, with about 5% available to replace inorganic fertiliser, equivalent to 15kg N/ha (12 units/acre) from a 50t/ha dressing.

The work has now been scaled up on two sites in Staffordshire and Yorkshire, which will stage open days later this spring. Application rates of 50cu m/ha (4500gal/acre) are being tested, with liquid going through either a £2000 Tramspread boom or a £24,000 contractors machine.

Inorganic fertiliser will be applied to top up nitrogen to the recommended level and sites yield mapped to show differences in crop performance.

Dr Shepherd admits that some growers are very sceptical about applying slurry and more particularly sewage sludge to cereals in spring. "People are concerned about pathogens and metals. But we are using treated sludge and following the ADAS safe sludge matrix. Parallel research will use laboratory techniques to monitor any risks." &#42

MANURE/ SLUDGE USE

&#8226 Use manures and sludges to cut NPK bills by £50/ha+.

&#8226 Spring application makes available more of the nitrogen in slurries and sludges.

&#8226 Impact of pathogens and metals being monitored.

Open days

Hattons Farm, Coven, Wolverhampton May 18 and Hornby Castle, Bedale, North Yorks May 25. Tickets free from ADAS Gleadthorpe (01623 844331).