Trawl the internet for trials data on the use of composted green waste in agriculture and there is plenty of material from the USA and some other European countries to chew over.
Organisations with an interest in recycling generally and composting in particular are getting to grips with the need for UK trials.
“So far, most composting initiatives have been marketing their product as soil improvers, primarily within the local hobby gardening sector,” says Francis Rayns of the Henry Doubleday Research Association (HDRA), Coventry.
“It is likely that compost will be used for landscaping but in the long term, the most important market will undoubtedly be agriculture.”
Persuading farmers to take, let alone pay for this material will take some effort.
It is generally accepted that green waste compost can provide plant nutrients and organic matter that improves water retention and erosion resistance on light soils. There is also evidence of microbial activity controlling certain soil-borne diseases such as take-all in wheat and carrot sclerotinia.
More trials are being established to define and quantify those benefits.
The HDRA, for example, is leading a four-year project studying the effects of green waste compost on plant growth, yield, soil nutrient status, soil structure and environmental impact, including an organic vegetable field trial and two on-farm trials – one organic, one conventional arable.
Remade Essex, one of several regional organisations developing local markets for recycled waste, has commissioned work on the benefits of compost for arable crop production on a heavy land farm.
“Agriculture has the potential to consume vast quantities of compost, and it will be essential that it does given the amounts likely to be produced in future,” says Ben Dyson of Remade. “We need to establish its credentials if farmers are going to take the product seriously.”
Promising indications from the first year, evaluating the effects of zero, 100t, 200t and 400t/ha compost applications on oilseed rape ground, include improved crop establishment and a contribution to the crop”s nitrogen needs.
Assessment of crop colour and vigour indicated that 100t/ha of compost supplies about the same nitrogen as 40kg of inorganic fertiliser. Only 5% of the total nitrogen was absorbed by the crop, confirming its slow release characteristics.
This rate also gave the greatest increase in leaf phosphorus and potassium content and gave the best yield response – up from 1.62t/ha to 2.53t/ha without additional nitrogen.
Increasing the amount of compost further did not add to the yield response. The optimum treatment was 100t/ha compost with 120kg/ha inorganic nitrogen. “We”ve looked at using compost for wheat production on the same heavy land farm and this year are starting a WRAP-funded trial on light land to assess compost use for high value cropping,” says Ben Dyson.
Enviros Consulting has just completed what it believes is one of the most comprehensive studies of compost use on agricultural land in Britain. Funded by waste management company Shanks with the support of the British Potato Council, the three-year project involved seven fully replicated trials and a range of crops.
“Among other things, the trials showed that soil properties could be improved,” says Phil Wallace of Enviros. “Organic matter levels were raised, as were plant available nutrients, principally potassium. Slow release of nitrogen from the compost was confirmed, so there is little risk of nitrate leaching.”
Increases in soil biological activity were evident from lab and field tests and improved water holding capacity was demonstrated on the site.
“Yields were raised by 6% on average, with potatoes showing a good response,” adds Mr Wallace.
“Such high value, irrigated crops grown on light textured soils are likely to give economic returns from the use of compost.”
“What”s important is that agriculture shouldn”t be seen as a dumping ground,” he says. “Farmers need to be offered a decent, consistent product with proven benefits.”
The work continues over the next two years, investigating the effects on soil structure and nitrogen turnover.