The assessment of amendments in composting to meet the requirements for the horticultural and agricultural sectors

This report addresses and completes the activities highlighted under Project 4 of the Deliverables for the Grant Scape Funded Project entitled “Quality Improvements and Use of Difficult waste in large Scale Composting”. The use of amending mature green compost using vermicomposting techniques was analysed using two 2.88 m2 reactors and a high worm loading of 7kg/m2. Over an 18 week period about 500 kg of compost was processed and a worm reduction to a loading of only 1 kg/m2 was observed. Growing trials observed that a mixture of this processed material with traditional green waste compost gave slightly improved results, but were not seen as being significant. For the horticultural sector production costs at £205/tonne were not sustainable in the current market. The use of vermicompost for the agricultural sector was undertaken in both glass house and field trails using wheat. The vermicompost was produced by feeding in-vessel co-composted green waste and biosolids earthworm beds containing approximately 5.0 kg worms/m2 housed indoors and measuring 2x2x0.3m. Studies show that vermicompost additions to soil at typical farm application rates did not cause an increase in crop yield. This might imply that vermicomposts are of little short term direct benefit to farmers, but it is likely that vermicomposts may have some long-term indirect effects such as replenishing soil organic matter and micronutrient reserves and inducing plant pathogen resistance. This material may have a role to play in integrated nutrient management systems designed for cereal farming, however, results suggest the benefits may be longterm and indirect which may ultimately reduce the market price for vermicomposts and lessen farmer acceptance of their use. The use of vermicompost amendments has a negative financial impact with net margins without fertiliser varying from £12.2/ha to - £11,205.8/ha depending on the amount of compost applied. A large scale trial was undertaken using a mixture of green waste and chicken litter to simulate a commercial operation. Respiration rates were significantly reduced due to the chicken litter blocking the free air space within the windrow, hence increasing operational time. Severe local odour issues arising from anaerobic conditions within the pile were observed. Productions were estimated to be about £36/tonne, but public acceptability of the product would be an issue.