STILLDOUBTSOVERSLURRYINJECTION…
STILLDOUBTSOVERSLURRYINJECTION…
SLURRY injection has won warm approval from the environmentalists, but many livestock farmers remain unconvinced.
The first choice for most farmers with large quantities of slurry to deal with are vacuum tankers, plus self-moving irrigators for dirty water and other low dry matter wastes.
Both have a number of advantages including a relatively low capital cost, but they are under fire from critics who say they can cause serious environmental problems.
The obvious problem is the smell nuisance. Tankers and irrigators achieve their spreading action by spraying the liquid in the form of droplets, and this happens to be an efficient method for releasing the gases which we detect as a smell.
Less obvious, but of more concern to the environmentalists, are the chemicals released as part of the smell. The list includes ammonia, which is released very rapidly during the spreading process. After the gas is released it can travel for long distances in the air currents, but eventually returns in the form of acid rain.
Some of the ammonia released in the UK is from non-farming activities such as manufacturing industry and power stations, but farming is easily the biggest source accounting for about 70% of the total.
The other by-product gas which worries environmentalists is nitrous oxide (N2O), which is one of the gases contributing to the "greenhouse effect", but as this is produced mainly by chemical reactions in the soil, it is linked to the quantity applied rather than the method of application.
Changing application methods away from equipment which releases droplets into the air could reduce ammonia production during spreading by about 50%, and this would be a significant step towards meeting Britains target for cutting ammonia emissions to reduce acid rain.
In Holland the link between application methods and environmental damage has already resulted in a ban on all forms of surface spreading, other than the trailing shoe type spreader – and the trailing shoe system is likely to be moved on to the banned list soon, according to Ian Scotford of the Silsoe Research Institute (SRI).
"Soil injection is the preferred method of application in Holland, and I believe the approval for the trailing shoe applicator will be withdrawn," said Mr Scotford. "Holland is the only country in Europe which has taken such drastic action over application methods. I am not aware of any plans in this country to follow their example."
Soil injection is at the top of the list for reducing gaseous emissions and the complaints from down-wind neighbours. This applies particularly to equipment for deep injection which puts the liquid 150mm or more below the surface. Using shallow injection techniques at up to 50mm depth is slightly less effective, but is more likely to be acceptable on grassland.
Other alternatives available to contractors who aim to provide their customers with an environmentally friendly slurry application service include dribble bars and the trailing shoe spreader. Both drop the slurry on the soil surface, and both avoid producing the airborne droplets which cause gaseous release during the application process. Both can also be used to spread the slurry beneath a crop canopy, slowing the wind movement over the newly spread liquid and helping to reduce the ammonia and smell release.
If slurry is spread on bare soil, the advice in the Managing Livestock Manures booklet is to incorporate the liquid into the soil, ideally within four hours of application, but certainly within 24 hours.
Even adjusting the splash plate to lower the spreading trajectory on a tanker can help to reduce the gaseous release problem, says Mr Scotford.
"Instead of adopting the Dutch policy of strict legislation, we are taking a more positive approach by emphasising the financial benefits available to farmers who reduce ammonia losses during and after spreading," he says. "Avoiding ammonia release means more nitrogen is available for crop growth, and this can allow savings in the amount of fertiliser applied."
The official estimate is that the slurry from 100 cows housed through the winter could be worth £2000 as a replacement for purchased fertilisers, and the aim is to persuade farmers that it is worth taking extra care over management and spreading to achieve savings on this scale. *
Injection buries many of the disposal problems – as well as the slurry.
Surface spreading, especially on short grass, is out of favour
with environmentalists.