Two Somerset dairy producers have proved composting manure can yield benefits in terms of soil health and reduced weed burdens, as Aly Balsom reports
Improving the aerobic function of farmyard manure by composting can boost its overall value by 20-fold and significantly enhance its contribution to soil nutrient cycling.
In fact, independent consultant Josephine Scamell explains how one tonne of composted manure can replace 20t of raw, undigested farmyard manure (fym).
“According to US research, there is significant scope for producers to get more from manure by making the most of natural microbial function; we’re missing a trick by not composting,” she says.
And this is a view shared by two producers in the South West, including Simon Madge of Manor Farm, Seavington St Mary, Illminster, who says accelerated composting has significantly boosted soil health on his farm.
“I don’t regard compost as fertiliser, it’s more a soil conditioner. Soil structure looks better and healthier and worm numbers have definitely increased,” he says.
What makes the difference between a conventional stack of fym and composted material is the introduction of air to promote natural microbial activity. By turning fym regularly, the composting process will be accelerated.
Mr Madge, who farms 240 cows, composts 800t of straw from loose housing every year with heaps turned four to five times a year using a specialist Windrow machine.
The machine is commonly used to handle green waste for the council and works by fully aerating the compost piles by turning the material from top to bottom.
“We used to compost to some extent using a rear discharge spreader, but by contracting out we are accelerating the rate of composting and it is much quicker and easier to do,” he explains.
At Manor Farm, compost is spread on arable ground in the autumn and grassland in the spring. “Compared with two years ago, soil condition is better and yields have improved,” says Mr Madge.
Although currently running an organic system, he says even if he changed to farming conventionally, he would continue using compost and not using fertiliser.
Mrs Scamell explains how applying compost to ground actually results in an assimilation of nutrients, rather than the nutrient loss you may expect
“The microbial activity in the soil will actually combine with that in the compost, hugely enhancing the nutrient assimilation capability of the soil. So by applying compost, nitrogen and carbon fixation from the soil and atmosphere will actually increase, and trace element availability will also be enhanced,” she says.
“Farmers may not be aware how much they are missing by not composting fym. By composting you are changing what is essentially a hazardous waste into a nutritious, hygienic compost.
“The humus in compost not only stimulates growth, it also enhances the carbohydrate metabolism of the plant to increase the amount of sugar produced – something which is important for producing high-quality forages,” she says.
Research by Linda Maria of the Massachusetts Institute of Technology has found up to 120lb (55kg) of nitrogen can be fixed an acre a year. In fact, there is the potential to provide all nitrogen requirements through fixation in bioactive soils, says Mrs Scamell. “This is a similar principle to nitrogen fixing in clover,” she says.
Research shows an average 50-100% more root nodules in legumes grown in fields where compost has been applied, explaining why less additional nutrient applications are needed in bioactive soils.
However, for Holt Farms, Blagdon, one of the most significant benefits of composting material is the removal of any detrimental weed seeds carried in the slurry.
Farm manager Jon Wilson comments: “Because we are organic, we can’t spray for weeds, so the main reason we compost is because we want to get rid of seeds.”
The microbial activity in the composting process digests any weed seeds, explains Mrs Scamell. “The heat generated by biodigestion also acts to kill any seeds, nemotodes and fly larvae and has also been proven to eliminate infectious bugs such as E coli and salmonella,” she says.
At Holt Farms, any compost accumulated in spring and summer is applied to autumn sown crops such as winter wheat or triticale at a rate of about 15-20t/ha. Spring barley also has compost incorporated into the top two inches of soil. In fact, Mrs Scamell says the crops at Holt Farms are among the cleanest she has ever seen because of the application of compost.
The farm uses the same machine as Mr Madge to speed up the compost process. Mary Mead, owner of Holt Farms and co founder of Yeo Valley Organics, says using this accelerated composting method is a way of speeding up how farmers used to traditionally deal with fym.
“With the old method, piles of fym in the field took a lot longer to compost and there was the temptation to spread before material hadn’t fully broken down,” she says.
Holt Farms has 420 cows split across two units, Holt Farm and Yoxter Farm and have recently installed slurry seperators on both units to split out the solid and liquid elements from cubicle housing. The solids and fym from pre-calving loose housing pens are then stacked in lines in fields for composting.
The liquid from the separation process is applied to grassland or winter sown arable crops when it’s dry enough, using an umbilical system or tanker, explains Mr Wilson.
“The liquid infiltrates into the soil much quicker versus slurry which can just sit of the top, giving off ammonia and losing nutrients through volotisation.”
One year the farm also composted excess grass that has got wet. “This way, when you are pushed into it, you can make more from waste,” says Mr Wilson.
Composting at Holt Farms:
- A slurry separator splits out the solid and liquid elements
- The solid part is heaped in lined in fields
- Heaps are turned using a Windrow machine up to six times over an eight-week period.
- Heaps are not turned at all from September to February during wet weather
- Location of compost heaps must be changed year on year
- The aim is to produce a black, compost of a similar consistency to that bought from a garden centre
- Any compost accumulated in spring and summer is applied to autumn sown crops at a rate of 15-20t/ha
- Spring barley has compost incorporated into the top two inches of soil
- The heat generated by composting kills any weed seeds in fym, reducing weed levels in crops post-spreading
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