Cropping of Miscanthus in Central Europe: biomass production and influence on nutrients and soil organic matter

The objective of the present study was to investigate the impact of biomass development of Miscanthus x giganteus (Greef et Deu.) on the concentration of plant nutrients and the accumulation in soil as well as quality of soil organic matter (SOM). Field trials with 4-9 year-old Miscanthus stands were investigated and sampled at four experimental sites in Germany in the years 1994 - 1999. From 1994 to 1996 the above-ground standing biomass at the end of the vegetation periods ranged from 14.8 to 33.5 t ha (- 1) dry matter (DM). The below-ground growing biomass (rhizomes, roots) reached 15 to 25 t DM ha - I (before sprouting in spring). Mean pre-harvest losses (harvesting date: February/March of the following year) of 4.5 t DM ha (-1) originated from senescent leaves and shoot-tips fallen to the ground during winter. This amount corresponds to about 26% of the whole above-ground biomass (harvested biomass + pre-harvest losses + harvested residues). Direct harvested residues (stubble mass) varied between 0.7 and 3.1 t DM ha(-1) Therefore 23-51% of the biomass grown could not be harvested. The mean harvested biomass was 11.7 t DM ha (-1). The largest concentrations of N, P, K and Mg in plant materials were observed in the pre-harvest losses. whereas the harvested biomass had the lowest concentrations. The concentration or nutrients in the harvested biomass was 61% (N) 64% (P), 55%, (K) and 50% (Mg) of the concentration in the biomass at the end of the vegetation period. These differences are explained by nutrient losses due to fallen leaves and shoot-tips and nutrient translocation into below-ground plant parts. The higher concentrations of plant available K in soil indicate that Miscanthus cropping enhances the cycling of nutrients in the plant-soil system. As a result or the high input of leaves, rhizomes and roots, the sandy soils were characterized by increased concentration or organic carbon (C-org; mean: + 2.0 g kg (1) and total nitrogen (N-t: mean: + 0.2 g kg (- 1)). The storage of SOM in topsoils was increased by 11.7 t ha (- 1). Moreover, the Miscanthus residues affected the quality of SOM. In a plot with Miscanthus, increased proportions of alkanes, alkenes, sterols and free fatty acids were observed by pyrolysis-field ionization mass spectrometry. (C) 2001 Elsevier Science BN. All rights reserved.