Applications of slurry are likely to have higher levels of nitrogen this spring due to low winter rainfall, leading to calls for producers to recalculate top-up rates for crops.
Met Office figures suggest most UK regions had just 70% of rainfall normally expected for Dec/Jan, and this has had a knock-on effect on dilution of manure and slurry in open farm stores.
Industry figures suggest a 2500 litres/ha (1000gal/acre) application delivers 10kg/ha (8 units/acre) over a typical winter, but where rainfall falls by 30%, this can rise to 17kg/ha (14 units/acre) with later application dates – an increase of up to 75%.
Ensuring nitrogen applications don’t exceed crop needs or groundwater limits in areas including Nitrate Vulnerable Zones is a concern, say advisers.
Typically, nutrient values for slurry are based on 6% dry matter.
But it is likely that many will be higher – increasing amounts of available nitrogen, according to Gillian Young, dairy consultant with Devon-based The Dairy Group.
At a recent DEFRA-funded workshop held with dairy processor Mller, at Market Drayton livestock mart, Shrops, 31 slurry samples taken from suppliers’ farms suggested there was a significant financial benefit from using higher available nitrogen content of slurry.
“With artificial fertiliser around £170/t each extra unit of available nitrogen is worth almost 50p/kg,” calculates Miss Young.
Dairy producer Derek Wright of Pritch Farm, Broom Hall, Nantwich, was among participants whose slurry tested with a higher-than-expected nutrient content.
“Slurry from the cubicle house tested at 18 units/acre when applied at 1750gal/acre.
Based on current fertilizer price that’s worth about £4.50/acre,” he says.
Mr Wright hopes to factor in the nutrient value, having applied slurry across most of the 210-cow herd’s grazing and silage area in recent weeks.
“There’s a lot of potential nutrient to utilise.”
Where testing before application is not possible producers can still take action, says John Morgan of Devon-based Creedy Associates.
“Place buckets within the areas slurry is applied and have it tested soon afterwards.
“This will at least give a value that can be factored in to crop’s total nitrogen requirement for the season.”
That’s particularly important for NVZs where nitrogen applications are capped at 250kg/ha (200 units/acre) annually for grassland.
Attention to phosphate and potassium indices should be considered, adds Mr Morgan.
“There’s little gained from applying slurry naturally rich in these nutrients to grassland with indices of 3 and 2, respectively.
Make best use of the total nutrients and – where possible – apply to crops such as cereal or maize that can make best use of these resources.”
South-west based independent consultant Jo Scamell says producers could increase the value of slurry further by slit cultivating grassland.
“It’s possible to get an improvement of 30% in utilisation of nutrients.
“A 6-8in slit prunes the sward’s lateral roots encouraging growth, allows slurry to get down to where it is needed, improves soil aeration and is the most basic, impossibly easy thing to get right.
“Don’t go mad rolling grassland.
This can cap soil turning the root zone anaerobic and leaving slurry sitting on the surface – that will impact heavily on palatability of grass during grazing and hit production,” she warns.