Benefit from holding on to muck and slurry

Livestock farmers are increasingly under the spotlight when it comes to greenhouse gas emissions and climate change. But in recent years they have dramatically cut their emission levels and, by doing even more, could save both money and the environment.

“Since 1990, emissions of nitrous oxide by UK agriculture have declined by 23%,” says Karen Wonnacott, DairyCo research and development manager. “Over the same period, ammonia emissions by dairy cows have been reduced by 13%, due in part to greater attention to the appropriate storage, handling and use of manures.”

As part of the dairy industry’s commitment to reducing its carbon footprint, DairyCo is promoting initiatives to help farmers improve their environmental performance and boost their profits at the same time. It has produced factsheets and case studies to highlight areas where farmers can make cost savings and reduce their emissions.

“Good muck and slurry management is key to reducing damaging emissions of nitrous oxide, ammonia and methane, all of which contribute to global warming,” says Dr Wonnacott. “And by keeping as many of the nutrients as possible locked up in manure, farmers can boost its fertiliser value and increase their grass and crop yields. It is a win-win for everyone.”

Although ammonia is not strictly a greenhouse gas, it dissolves in rain when released into the atmosphere and then deposits to land, resulting in nitrous oxide emissions. In the UK, agriculture accounts for more than 85% of total ammonia emissions, one-third of which comes from the dairy sector.

“Ammonia emissions during livestock manure management are typically in the range of 10-20% of the nitrogen excreted by dairy cows, representing a large loss of agronomically valuable nitrogen.”

Allowing a natural crust to form on slurry will cut ammonia emissions in half, while covering slurry stores and farmyard manure heaps will slash emissions by up to 90%, she adds.

Slurry and manure applications are another area where massive savings can be made. “Rapid incorporation of slurry or manure by ploughing straight after application can reduce ammonia emissions by up to 90%. Applying slurry using a trailing hose or shoe will cut emissions by 30-60% compared with surface broadcast application, while shallow injection will reduce ammonia losses by 70%.”

Nitrous oxide, which is about 300 times more harmful than carbon dioxide, is another by-product of farming and accounts for as much as three-quarters of all UK emissions. “The dairy sector is responsible for about 17% of that, often through the loss of nitrogen in manure and slurry applications,” says Dr Wonnacott.

“Typically, about half the nitrogen content of slurry is present as readily available ammonium nitrate. Applying slurry in autumn, when crop growth and nitrogen uptake are slow, will increase the risk of nitrous oxide emissions and winter nitrate leaching. In contrast, applying slurry in spring, when crop growth is rapid, will increase the amount of nitrogen used by crops.

“Changing your slurry application from autumn to spring will, therefore, increase its fertiliser value almost threefold – a valuable saving given the cost of inorganic nitrogen.”

For optimum savings, farmers should measure and plan their nutrient applications, targeted at the crop and soil requirements. “The industry has committed to reaching Milk Roadmap targets which require 95% of dairy farmers to have a manure management plan, and for 65% to be actively nutrient planning by this year. We are on target to reach that – and the benefits to both farmers and the environment can be huge.”

South-west farmer David Munday has saved £200/ha by accounting for the nutrient content of manures applied to maize ground, and cut fertiliser costs on his wheat crops by 27%, explains Dr Wonnacott. “By analysing your slurry and your soil, you can more closely match the crop’s nutrient needs and availability,” she says. Slurry and manure are rich in potash and phosphate, and are good soil conditioners due to high organic content.

This has enabled Mr Munday to slash his fertiliser costs, reduce greenhouse gas emissions and improve his maize yields and silage quality. “Saving the environment and reducing input costs does not have to be expensive – just a few simple changes to your system can yield dramatic benefits.”