Woodchip will need to be reused several times as bedding for livestock before it becomes a useful fertiliser.
Research at IGER, Aberystwyth, has shown that simply composting for six months after using once is not good enough. In contrast to straw-based farmyard manure, impractical large volumes of compost must be applied to replace standard nitrogen dressings for crops.
IGER researcher Rhun Fychan and Myers Paul of Bangor University told visitors at a soil fertility demonstration that woodchip had been used for eight weeks to bed either bulling heifers, or yearling ewes, fed either hay or silage. Identical animals on the same forages were housed on straw. All the bedding was collected and composted for six months during the summer of 2006.
After storage in bags over winter, compost was analysed and scientists calculated how much had to be applied to spring barley plots to supply 75kg/ha of nitrogen.
Composted straw bedding from cattle fed hay and straw had to be applied at the rates of 6453kg and 5018kg/ha. The equivalent weights for composted woodchip from under cattle were 17,668kg and 16,308kg/ha. After composting, the required weights of straw bedding from sheep fed hay and silage were 6447kg and 4366kg/ha. The required application rates of composted woodchip from under sheep were 10,977kg and 10,084kg/ha.
More barley tillers were produced when straw-based composts were used. “It’s clear that woodchip needs to be reused two or three times to allow it to absorb more nitrogen and to break down larger chips,” said Mr Paul.
The best advice was not to apply chips to land until they had broken down to a fibrous loamy material. To ensure effective composting, new woodchip should not be mixed with once- or twice-used material.
Mr Paul also suggested farmers could cycle material over several seasons until they had a regular supply of well-composted nitrogen-rich compost.
Woodchips need reusing several times before being used as a substitute inorganic fertilser, according to research at IGER, Aberystwyth.