A new set of quality standards for compost coming into force next month will ease the regulatory burden on growers and could lead to an increase in its use on farm.
From 7 May, any compost produced to Quality Protocol for Compost standards will not be classed as waste, so growers in England and Wales spreading it on land will not have to register with the Environment Agency for a waste exemption. Rules remain unchanged in Scotland, where compost meeting the existing British PAS100 Standard is already not classified as waste.
An estimated 0.6-1m tonnes of compost is used on-farm each year, which is small compared with the 90m tonnes of animal manure used. But ADAS soil scientist Susie Holmes expects this will increase.
“The amount of compost applied on-farm is definitely growing, as people are increasingly looking to agricultural uses. The new quality protocol will certainly help this trend continue.”
She believes the low available nitrogen content of compost – typically 5% N in the first year – makes it an environmentally-friendly way of improving soil organic matter, which is now required under cross-compliance. “Nitrogen leaching will be less of a problem and the organic matter is also in a more lignified form, so it lasts longer in the soil than many animal manures.” It also improves workability and water-holding capacity, she says.
Bagged nitrogen savings are unlikely to exceed 15kg/ha in the first year because of the low nitrogen availability, Mrs Holmes acknowledges, but there could be other savings in phosphate and potash. “One fresh weight tonne of compost typically contains 3kg phosphate and 6kg potash and quite a large percentage will be available to the crop in the first year.”
Sandy soils in particular, may benefit because they are often low in potassium as well as needing extra organic matter to improve water holding, she says. “But even heavier soils can benefit from improved workability.”
But proximity to composting sites remains one of the main factors inhibiting use on farms, Mrs Holmes recognises. “Compost is so bulky you can’t transport it too far. That’s where on-farm composting is a real benefit.”
In many cases, if farmers have a site nearby and are willing to collect compost themselves, they will be able to have it for free, she adds. “The cost of spreading is about £2.50-3/t, but you would easily get that back from the nutritional value it delivers.”