Effect of the organic residues of Miscanthus x giganteus on the soil organic matter level of arable soils

During a complex investigation programme on the evaluation of the long-term ecological impact of cropping Miscanthus, the substrate composition of residues in 4-8-year-old stands of Miscanthus x giganteus and the contribution of Miscanthus residues to soil organic matter (SOM) were investigated. Only about 50% of the aboveground biomass produced yearly was suitable for harvest because of pre-harvest losses and harvesting residues. The potential supply to SOM was therefore 3.1 t ha(-1) carbon annually accumulated by the litter, and 9.1 t ha(-1) carbon accumulated by rhizomes and roots in the long term. These organic residues mineralized differently in laboratory experiments at generally high rates of decomposition. Analysis of soluble portions of the organic substance of these biomass components by hydrolysis with hot water, 2% HCl and 80% H2SO4 confirmed the results. Setting the SOM effect of an equivalent farmyard-manure (FYM) supply to 100%, Miscanthus residues reached 60% (stubble, rhizomes), 80-90% (pre-harvest losses) and 100% (roots). Established Miscanthus stands are able to produce about 8.2 t ha(-1) organic substance, which is comparable with FYM in terms of SOM impact. This kind of calculation showed higher values for Miscanthus than for the agricultural crops investigated to date. An SOM increase of about 0.5% on sandy soils and 0.2% on silt soil was determined after 6-8 years of cropping Miscanthus x giganteus.