Combined production of biomass for energy and clean drinking water - A miscanthus demonstration project on the Renewable Energy Island Samsø

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1 Combined production of biomass for energy and clean drinking water - A miscanthus demonstration project on the Renewable Energy Island Samsø Uffe Jørgensen, Danish Institute of Agricultural Sciences, Department of Crop Physiology and Soil Science, P.O. Box 50, DK-8830 Tjele. uffe.jorgensen@agrsci.dk Introduction The island of Samsø has been elected as the Danish Renewable Energy Island with the aim of 100% self sufficiency with renewable energy within year The island is supposed to become a showcase for Danish renewable energy technology (see The biomass resource of the island is however scarce due to intensive horticultural production and a rather small forested area (Jørgensen & Christensen, 1999), and there is a need to produce more biomass for the heating plants established or under construction. Recent research at the Danish Institute of Agricultural Sciences has shown that nitrate leaching from the perennial energy crops willow and miscanthus is considerably lower than from traditional agriculture (Jørgensen & Hansen, 1998; Mortensen et al., 1998; Jørgensen & Mortensen, 2000). Additionally, pesticide use is low and may even be avoided by mechanical treatment of weeds (Jørgensen & Mortensen, 2000). Miscanthus is not as commercially developed an energy crop as willow, and there is a need for further experience and development especially of the crop establishment. Miscanthus establishment was originally done by plantlets, which however showed up to be both too expensive and too unsafe as several large plantings in northern Europe did not survive the first winter (Jørgensen & Schwarz, 2000). Recently, the company Nordic Biomass has developed a specific planting machine for miscanthus rhizomes (Kristensen, 1997). This has completed an establishment system that cuts costs by at least 80% compared to planting of plantlets (Schwarz et al., 1998). The system has been tested in small scale in the UK and in Denmark, but more experience is necessary before large plantings can be planned for. In year 2001 the Danish Energy Agency sponsored establishment of approximately 20 ha miscanthus on Samsø, and the county of Århus sponsored the establishment of a soil water sampling station to follow nitrate leaching from two management systems of miscanthus and from a neighbouring crop rotation. This paper presents the project experiences and results so far. Planting 20 ha were selected for the project among interested farmers on the island. The farmers were responsible of preparing the fields properly before planting. Nordic Biomass (NB (formerly Hvidsted Energy Forest )) in co-operation with the Danish Institute of Agricultural Sciences (DIAS) delivered and planted miscanthus rhizomes. Subsequently the farmers are responsible of crop management, harvest and sale of miscanthus for local heating plants. However, DIAS will be available for advise on weed treatment etc. Rhizomes for the project were harvested from fields on Funen. The fields were raked free of leaves before rotary cultivation to break up the rhizomes into pieces of a suitable size for planting. Rhizome harvesting was done with a Grimme stone picker (Fig. 1). This worked quite well on the more sandy soils, but due to a very wet spring the more loamy soils caused major problems, and at some fields harvesting was impossible. In general the wet conditions caused a high soil fraction with the rhizomes and that more rhizomes were left in the field compared to earlier experiences.

2 Fig. 1. Rhizome harvesting with a Grimme stone picker on a sandy soil in spring Rhizomes and soil was loaded into 15 m 3 containers that were transported by lorry to Samsø. Planting took place from May 14 to 22. Only 12.6 ha were planted because the amount of rhizomes taken up was lower than expected. The wet conditions were one reason for this. Another reason may have been that rhizomes on better soils are distributed deeper into the soil than on the sandy soils where experience on rhizome harvesting has taken place so far. Therefore a lower fraction is harvested when only 15 cm working depth is used for cultivation and harvesting. The planting process in general worked well and approximately 4 ha per day were planted (Fig. 2). However, on stony fields the coulters were damaged several times indicating a need for mounting of stone-release equipment. The fields were very variable in texture, which caused no major differences in planting performance. However, on one minor area of very heavy clay the furrows were not well closed after planting, which caused a poor contact between rhizomes and soil, and a subsequent low plant establishment. Fig. 2. Rhizome planting on Samsø in spring 2001 with the planter from Nordic Biomass.

3 Sprouting and subsequent plant development was good in the mild climate of Samsø. However, in general the plant number on the fields was too low, which was a result of the low amount of rhizomes in the planting material. In the first year miscanthus has very low competition upon weeds and row cultivation and/or chemical treatments were applied in most fields. Ground water protection Part of the land planted with miscanthus is situated in an area with specific restrictions due to important drinking water resources. Earlier results have shown that nitrate leaching from miscanthus is low when the crop has established (Fig. 3), and therefore a specific project on the demonstration of environmentally friendly agricultural measures was initiated in spring Suction cups were established to measure nitrate leaching from three different fields: 1. Miscanthus recommended fertilisation and herbicide use 2. Miscanthus reduced fertilisation, fodder radish catch crop sown mid August in year 1 and preferably mechanical weeding 3. Crop rotation Early potatoes 2001, ryegrass catch crop sown mid July juli 93 januar 94 juli 94 januar 95 juli 95 januar 96 juli 96 januar 97 juli 97 januar 98 juli 98 januar 99 juli 99 januar 00 mg NO3-N/l 0 N N (NPK) N N (NPK) N (liquid manure) N (liquid manure) Fig. 3. Concentration of nitrate-n below miscanthus at different fertiliser-application since establishment in 1993 at Research Centre Foulum. The first results are shown in Fig. 4 with a clear difference between the three treatments. Nitrate concentrations below miscanthus without catch crop were initially lower than in earlier investigations (compare Fig. X and Y), which may be due to the good crop establishment from rhizomes. The catch crop of fodder radish seems to be very efficient in collecting surplus nitrate in late autumn, which is in line with Thorup-Kristensen (2001), who found this crop to be the most efficient catch crop under Danish

4 conditions and much more efficient than Italian ryegrass. However, a longer time period is necessary to draw real conclusions from the results. This project on monitoring of leaching will continue for several years in contrast to the planting demonstration, which finishes after replanting in spring mg nitrate-n/l Crop rotation Miscanthus Miscanthus + catch crop Fig. 4. Concentration of nitrate-n below two miscanthus treatments and a neighbouring agricultural crop rotation at Samsø. Summary The project has produced the following experiences on miscanthus establishment: Rhizome harvest is best done on sandy soils The calculation of amount of rhizome material collected and planted is difficult and more experience is needed The planting machine is operational but there are several points for further optimisation, eg. Stone release on coulters So far the mild climate with low precipitation at Samsø seems to suite miscanthus well With respect to ground water protection the first results on nitrate concentrations are in line with earlier experimental results. A catch crop of fodder radish significantly reduced concentrations in the first year. References Jørgensen, P.J. & Christensen, E.L., Biomasseressourcer på Samsø. PlanEnergi, Århus, 90 pp. Jørgensen, U. & Hansen, E. M., Nitrate leaching from Miscanthus, willow, grain crops and rape. In: Proceedings of the IEA workshop on environmental aspects of energy crops production (Wörgetter, M. & Jørgensen U. eds.), BLT Austria, Jørgensen, U. & Mortensen, J., Combined energy crop production and groundwater protection. In: Do energy crops have a future in Denmark? DJF rapport Markbrug nr. 29, Jørgensen, U. & Schwarz, K.-U Why do basic research? A lesson from commercial exploitation of Miscanthus. New Phytologist 148,

5 Kristensen, E.F., Automatic Miscanthus rhizome planter, prototype. The European Energy Crop Internetwork, ( Mortensen, J. V., Nielsen, K. H. & Jørgensen, U Nitrate leaching during establishment of willow (Salix viminalis)on two soil types and at two fertilisation levels. Biomass and Bioenergy 15 (6), Schwarz, K.-U., Kjeldsen, J. B., Münzer, W. & Junge, R., Low cost establishment and winter survival of Miscanthus x giganteus. In: Kopetz, H. Weber, T., Palz, W., Chartier, P. & Ferrero, P. L. (eds.). Biomass for energy and industry, C.A.R.M.E.N., Rimpar, Germany, Thorup-Kristensen, K Are differences in root growth of nitrogen catch crops important for their ability to reduce soil nitrate-n content, and how can this be measured? Plant and Soil, 230,