Research brings change of tack to best slurry use
By Simon Wragg
FARMER-FUNDED research on maximising use of slurry has changed emphasis for muck management for one Cheshire-based partnership.
Stuart and Richard Yarwood say they were indoctrinated into the practise of using bagged fertiliser to maximise forage production. But rising fertiliser prices and investment in farmer-funded research has now put emphasis on making the most of muck and slurry.
The brothers run 200 pedigree Friesian Holsteins and followers at the 93ha (230-acre) Lower Midhurst Green and 45ha (110-acre) Handfield Farm, Congleton. Typical annual fertiliser rates applied to grazing and silage areas over the past decade have topped 400kg/ha N (320 units/acre), 19kg/ha P (15 units/acre) and 125kg/ha K (100 units/acre).
"In the past, we were unaware of the true value of slurry when applied to grassland," says Stuart. But with bagged N touching £135/t a few years ago, the brothers began to adopt recommendations from slurry trials conducted by the R&D group of the Cheshire Grassland Society (see panel).
"R&D trials suggest applying 3000gal/acre of slurry at the right time could give 20 units/acre of N and enough P and K to supply first cut silage," says Stuart. "The question in our minds was whether we could afford to cut bagged N applications and still maintain output from grass, as dairying is our main enterprise."
To minimise risk of under-supplying nutrients, soil tests were used to establish nutrient indices across grazing and silage areas. Using data from CGS trials, fertiliser rates have been recalculated taking into account nutrient content of both slurry and dirty water.
In the past, all first cut silage ground received 150kg/ha N (120 units/acre), 35kg/ha P (28 units/acre) and 62kg/ha K (50 units/acre) as a blanket treatment. Nitrogen applications have now been cut back by 25kg/ha (20 units/acre); both P and K indices are topped up with tailor-made compounds taking into account soil indices and slurry.
"On second cut silage ground applications of 80 units/acre were scaled back to 62 units/acre to improve silage quality, but where slurry has been applied at 3000gal/acre it is down to 45 units," says Stuart.
As well as slurry, dirty water is also being applied with an umbilical spreading system. "Dirty water has a lower nutrient value, but still gives about 10 units/acre N," says Richard. Timing of dirty water applications is being steered towards summer to reduce risk of burn-up, although this is not usually a problem. "But in worst years it could be the difference between having grass or not," he adds.
Like slurry applications, spreading dirty water with this system enables a more accurate application to be achieved compared with using a tanker. Greater accuracy is also achieved by recalibrating nutrient levels in summer and winter slurry, the latter containing more water.
Fertiliser cost cutting could be improved further by increasing slurry storage, the brothers maintain. "The system is not cutting fertiliser costs as much as it could. We have limited storage and still have to apply slurry to provide space rather than when it can be better used," says Stuart.
Despite storage limits, which should be rectified when a new 500,000gal slurry pit is completed in spring, use of manures has cut fertiliser costs by over £12.50/ha (£5/acre) for first cut silage ground alone.
"Our grassland society groups trials raised our awareness of slurry and confidence in using it by finding out what it is worth when applied properly," Stuart adds. *
• Save £12.50/ha (£5/acre).
• Timely applications.
• Umbilical spreading better.
A number of replicated trials have been conducted by CGSs R&D group over several years at Reaseheath College in Cheshire to assess slurrys potential. A summary of trial work completed to date includes:
• Amount of P and K in adequate slurry applications should be sufficient for first cut silage.
• 28,000 litres/ha (3000gal/acre) slurry plus 100kg/ha N (80 units/acre) gives best yields of early grass.
• Slurry applied at 28,000 litres/ha (3000 gal/acre) by Feb14 doesnt affect silage fermentation significantly.
• Applications of 150kg/ha N (120 units/acre) fertiliser often give lower yields than 125kg/ha N (100 units/acre).
• Injecting slurry gives best yield response, particularly in second cut silage ground.
• Analysis essential to establish amount of available N in slurry.