15 June 2001

Minimising environmental impact

Current research on minimising the environmental impact

from livestock was reviewed at a recent Sustainable Livestock

Production LINK workshop, Richard Allison reports

NITRATE levels in groundwater can be kept below the EU maximum of 50mg/litre by lowering nitrogen inputs and modifying land management on dairy farms, but profitability can suffer by 10%.

That is the message from a six-year project undertaken at ADAS Bridgets Research Centre, Hants, presented to researchers at a recent LINK workshop on the environmental impacts of modern livestock farming.

ADAS Bridgets researcher Paul Withers said reducing nitrogen losses into the environment by modifying slurry handling is expensive at £1.20/kg of nitrogen saved, particularly when considering fertiliser nitrogen only costs 30p/kg.

"This is not a cost-effective option for reducing nitrogen losses. Extra investment is needed to extend slurry storage capacity and contractor costs are higher for spreading slurry with specialised machinery.

"But there are other effective strategies which cost less, such as rapid incorporation of slurry in soil on maize land. In addition, implementing the RB209 fertiliser recommendations only costs £9/ha, but it requires improved management skills."

Mr Withers also outlined some examples where it went wrong in the project. "A mixed grass/clover sward was ploughed out in October instead of December, which is too early, increasing nitrate leaching.

"Another problem was that the residual nitrogen in the soil from the previous crop was underestimated for whole-crop wheat, resulting in too much fertiliser being applied. This demonstrates that it is not just a matter of reducing nitrogen input, but how you manage the land is also important.

"Maize was a key part of the environmentally improved system at Bridgets because it has a lower nitrogen content than grass silage, allowing a lower nitrogen diet to be fed to cows. Also, slurry can be rapidly incorporated in soil prior to sowing maize, virtually eliminating nitrogen losses as ammonia," he added.

The method of applying slurry on grassland affects ammonia losses. The trailing shoe technique deposits slurry beneath the sward, resulting in 60% less ammonia loss compared with broadcasting using a splash plate. But he explained that work rates were slower with the trailing shoe.

"To reach the target nitrate level in water, nitrogen inputs had to be reduced by 30%."

Mr Withers also highlighted that phosphorus losses are a major environmental issue. In the project, phosphorus inputs in feed and fertiliser were reduced, and the surplus fell from 32kg/ha to 3kg/ha, without reducing milk output. &#42

Changing the method of slurry application to grassland can reduce ammonia losses by 60%, says Paul Withers.

MINIMISING IMPACT

&#8226 Nitrate leaching reduced.

&#8226 Slurry equipment expensive.

&#8226 Not just reduced inputs.