Post-industrial landscapes bolster energy crops with the help of PAS 100 Compost

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1 Post-industrial landscapes bolster energy crops with the help of PAS 100 Compost As fossil fuel reserves decline and pressure mounts to reduce CO2 emissions, renewable energy is fast becoming the focus for a cleaner, more sustainable future. The UK faces challenging targets, but with the right soil improver, an increase in biomass production on brownfield land could not only bolster energy supplies, but also bring unproductive land back into use. Under the EU Renewable Energy Directive, the UK must generate 15 per cent of its energy requirements from renewable sources by 2020; no mean feat for a country that, in 2010, supplied just three per cent of its needs from sustainable sources. As new technologies come into play and a range of renewables limbers up to address the shortfall, biomass energy crops such as grasses and short rotation coppice willow are playing their part in the equation. Discussion on the long term pros and cons of transferring food-growing land to the production of biomass continues, but meanwhile attention is turning to the potential offered by brownfield land and, in particular, soils disturbed during mining. These soils tend to be in poor condition with low organic matter content and availability of nutrients. Historically bulky manures have been used to accelerate recovery, but availability of these is highly localised and seasonal. As a result, WRAP has been working in partnership with landowners and scientists to assess the viability of providing an alternative source of soil improvement in the form of commercially produced PAS 100 compost. These soils tend to be in poor condition with low organic matter content and availability of nutrients. Historically bulky manures have been used to accelerate recovery, but availability of these is highly localised and seasonal. As a result, WRAP has been working in partnership with landowners and scientists to assess the viability of providing an alternative source of soil improvement in the form of commercially produced PAS 100 compost. The trials described below were established to gauge the effectiveness of PAS 100 green and food derived composts as a viable improvement to poor quality soils on post-industrial sites. page 1 forward

2 When the Peel Group began to explore the possibility for growing biomass in the form of short rotation coppice on brownfield land in North West England, it needed to find a way to improve the poor quality of the soil. The resulting trial at in which PAS 100 food derived compost was incorporated into the soil showed increased soil nutrient values and highlighted the potential for derelict and brownfield land to play an active role in the growth of renewable energy crops. The substrate at Bickershaw was typical of deep mined colliery spoil sites; deficient in major nutrients and highly acidic. To successfully grow short rotation coppice (SRC), the soil needed to be improved to reduce bulk density; increase pore space; enhance moisture retention while improving drainage; increase organic matter content, and enhance the availability of major and secondary plant nutrients. Compost supplied by Fairfield Compost was added to comparative plots at the equivalent of 500 and 1,000 tonnes per hectare in order to sustain the crop for a period of three to four years. Prior to application, the entire site was treated with ground limestone to neutralise the acidity. Within a short time it was evident that the addition of the food derived compost had had a significant impact on the availability of nutrients. Potassium levels in the low rate application, for example, were recorded at 21 times the control rate, while the plot treated with the greatest volume of compost was shown to hold 44 times the potassium found in the control plot. Similarly, phosphorus rates were modestly higher in the high rate of compost. This is key, since phosphorus is typically unavailable to plants in colliery spoil due to a chemical reaction with high concentrations of ferric iron. Food derived compost was shown to offer a beneficial environment for the growing of SRC willow, compared with a number of organic alternatives such as paper mill crumb and sewage sludge which are also available. Evidence suggests that food derived compost is able to increase water availability more consistently than paper mill crumb. Equally, paper mill crumb has been shown to cause net immobilisation of soil nitrogen proportional to the rate it is applied, which would restrict the growth of SRC willow. Food derived compost would provide more than enough nitrogen over a period of three to four years. Although the application of compost at 1,000 tonnes per hectare saw dramatic results in some cases, the lower rate of 500 tonnes per hectare was perfectly adequate and was able to offer long term benefits to the crop for the required amount of time, establishing it as a valuable player in future restoration projects, and helping to convert poor quality land into productive energy growing sites. page 2 Bickershaw trial site

3 In 2006, WRAP commissioned trials at an opencast coalmine in Fife to demonstrate the potential for using PAS 100 compost to improve soil and growing conditions on a site recently reinstated after disturbance from opencast mining. Results showed that even three years after application, the areas treated with PAS 100 compost maintained a long term improvement in soil conditions. Environmental Advisor and project manager Debbie Neely said that under higher applications of compost, the site encountered a problem with grasses out-competing the trees. However, she expanded: The trees that did grow, grew a significantly greater harvest than the control, so if we had had better weed control to start with, we would have a huge harvest. is a working mine with a site restoration strategy that includes the planting of short rotation coppice willow. Poor, heavy soil quality and a tendency to water log presented a challenge which called for the addition of bulky organic material to improve conditions, restart biological activity and enhance soil nutrients. PAS 100 compost was applied, before planting, and at two different rates; 300 and 600 tonnes per hectare, with an equal volume of land left untreated to act as a control. Samples taken in December 2007 and throughout 2008 demonstrated that the treated plots contained substantial increases in organic matter, plant nutrient levels and ph values. Three years later, these benefits were still evident. The trial took advantage of reasonably dry weather conditions to spread the composts, using a 4-wheel drive tractor unit and walking floor, rear discharge spreader body. The design of the plots had a major impact on spreading by allowing the spreader to run the full length of one field, working at a single treatment rate. Low ground level traction also minimised the degree of smearing and rutting that occurred while spreading composts. coalmine after the application of PAS 100 compost page 3

4 Ctd. Plant nutrients such as phosphorus, potassium and magnesium also increased with the addition of compost, showing conclusively that PAS 100 could be widely recommended both as a solution to the long term improvement of soil structure and as a vehicle for providing crops such as short rotation coppice willow with the necessary nutrients and conditions necessary for vigorous growth. Visually it was extremely obvious within several months where the compost had been applied you could see exactly the different rows high, medium, and control the whole way across with the striped field. It was impressive. Debbie Neely, Environmental Adviser Cockle Park Farm at Morpeth, Northumberland, had a history of agricultural production before it was used for opencast excavation as part of the Butterworth Opencast Mine. When mining ceased in 1990, ongoing problems with restricted drainage, water availability and plant rooting meant that immediate restoration for agriculture without a major increase in soil fertility and structure was unfeasible. However, trials using PAS 100 food derived and green composts showed that the land could be improved, in conjunction with short rotation willow coppice grown as a biomass crop to provide an income. Conditions at Morpeth are typical of many restoration sites where compaction of finely textured and slowly permeable soils lead to poor drainage. Often, the solution is to introduce grass or forestry plantation until the soil is favourable for returning to arable, but this is a costly approach with no tradable return until the land is suitably remediated. Biomass crops such as willow coppice offer a viable and attractive alternative and are emerging as an important renewable energy source, particularly on poor quality land that is unsuitable for the economic production of food crops. page 4

5 Ctd. Although non-food crops are often well-suited to poor soil conditions, these sites tend to be low in available nutrients, requiring the addition of fertilisers to improve growth. Chemical fertilisers are both expensive and undesirable due to their dependence on fossil fuels. PAS 100 compost, on the other hand, not only offers a cheaper option, but also comes with the added advantage of increasing the reserves of organic matter in the soil helping to store moisture and nutrients. Both PAS 100 food derived and green compost were applied using a purpose-built plot spreader which had previously been calibrated to apply the correct rate on adjoining areas of coppice plantation. Food derived compost in particular was found to provide significant carbon offset benefits; it facilitated greater yields than green compost and also required a lower tonnage in order to provide optimum nitrogen dosage. This resulted in large savings in fuel use for transportation and spreading. Food derived compost also increased yields by 57 per cent compared to the untreated plot, and by the second season was comparable with the plot treated with sewage sludge. These results demonstrate a particular affinity with the coppice rotation system, where the opportunities for application of fertiliser are limited to post-harvest periods when access to land with machinery is restricted. Sewage sludge saw a marked increase in yield in the first year, but also resulted in an excess of nutrients such as nitrogen, phosphorus and magnesium and a rise in ph which, over time, may prove detrimental to crop nutrition balance and also cause weed problems. Initially, all applications appeared to act as a weed-suppressing mulch. Sewage sludge proved especially successful in this role, although in later months it appeared to encourage the growth of particularly aggressive weed species. Willow at SES In comparison, the lower level of available nutrients in the PAS 100 compost plots helped to discourage invasive weed species. This, combined with the slow release of nutrients which matches the demands of short rotation coppice over a three to five-year cycle, offers a great potential to build fertility in poor quality soils and has already proved a cost effective way to improve yields. page 4

6 This case study is one of a series of projects that examines the use of PAS 100 compost in biomass production on brownfield land For further information visit where you can access: the Good Practice Guide; tools and guidance; and a range of other case studies While steps have been taken to ensure its accuracy, WRAP cannot accept responsibility or be held liable to any person for any loss or damage arising out of or in connection with this information being inaccurate, incomplete or misleading. This material is copyrighted. It may be reproduced free of charge subject to the material being accurate and not used in a misleading context. The source of the material must be identified and the copyright status acknowledged. This material must not be used to endorse or used to suggest WRAP s endorsement of a commercial product or service. For more detail, please refer to our Terms & Conditions on our website - back : home Waste & Resources Action Programme The Old Academy 21 Horse Fair Banbury, Oxon OX16 OAH Tel: Fax: info@wrap.org.uk Helpline freephone