Petra Kahle

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×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−1 (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 of 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 of the high input of leaves, rhizomes and roots, the sandy soils were characterized by increased concentration of organic carbon (Corg; mean:+2.0 g kg−1 and total nitrogen (Nt; 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.

Long-term effects of short rotation forestry with willows and poplar on soil properties

Abstract Short rotation forestry is a promising tool for biomass production. In order to determine long-term effects of short rotation forestry on chemical, biochemical and physical soil properties we have investigated two former arable sites with willow and poplar clones (Salix and Populus spp.) in northeast Germany. The organic carbon and the total nitrogen contents of the sandy topsoil increased up to 4.0 g kg−1 and 0.2 g kg−1, respectively after 12 years. The C/N ratio was higher under short rotation forestry caused by the stronger C than N accumulation. The contents and reserves of plant available phosphorus and potassium were decreased significantly from the 6th to the 12th year, but the plant supply was still sufficient without fertilization. The pH in the topsoil was significantly lower under willow clones than under poplar clones. Higher dehydrogenase activity of the soil was measured under poplar and willows than at tree-less control plots. The bulk density decreased and the porosity of the soil increased under short rotation forestry. In conclusion the major long-term effects of short rotation forestry on arable used Cambisols were the accumulation of organic matter followed by slightly improved soil physical conditions and increased soil biological activity.

Soil organic matter composition of man‐impacted urban sites in North Germany

Human activity in the environment has great impact on soil ecology. However recent knowledge on properties of anthropogenic soils is still scarce. For this reason the purpose of this paper is to deliver data on the soil organic matter (SOM) properties of urban soils with an example from the city of Rostock (Northeast Germany) and to describe the environmental consequences of severe anthopogenic actvity. The results suggest that SOM of urban settings is significantly different in their chemical nature of humic compounds and their coal contents. The lower content of alkyl C and the simultaneously higher contents of aromatic C moieties in urban soils compared to their natural counterparts suggest a substantially different biochemical behavior against environmental hazardous compounds and microbial activity. This knowledge is essential for a qualitative assessment of important biochemical mechanisms in urban soils. Die Zusammensetzung der organischen Bodensubstanz auf vom Menschen stark veranderten innerstadtischen Standorten Menschliche Aktivitaten in der Umwelt haben einen grosen Einfluss auf die Bodenokologie. Trotzdem sind die Eigenschaften der anthropogenen Boden nur sehr begrenzt bekannt. Aus diesem Grunde versucht die vorliegende Arbeit, Eigenschaften der organischen Bodensubstanz (OBS) innerstadtischer Flachen am Beispiel von Rostock aufzuzeigen und einige okologische Konsequenzen abzuleiten. Die Ergebnisse zeigen, dass die OBS urbaner Boden sich deutlich in der chemischen Natur der Huminstoffe und/oder dem Kohlegehalt von naturlichen Boden unterscheidet. Der geringere Alkyl-C-Gehalt und gleichzeitig hohere Gehalt an aromatischen C-Molekulen der Stadtboden im Vergleich zu den naturlichen Boden lasst ein chemisch deutlich unterschiedliches Verhalten gegenuber umwelt-gefahrdenden Stoffen vermuten. Das muss bei einer bodenokologischen Bewertung urbaner Flachen beachtet werden.

Schwermetallstatus Rostocker Gartenböden

Zur Analyse und Bewertung der Schwermetallbelastung wurden die Gehalte an Cd, Cr, Cu, Hg, Ni, Pb und Zn von 32 Gartenboden des Stadtgebietes von Rostock untersucht. Gegenuber den ackerbaulich genutzten Boden des Umlandes ergaben sich erhohte Schwermetallgehalte. Insbesondere die Gartenoberboden wiesen aufgrund flachenhafter und punktueller Immissionen Schwermetallanreicherungen auf. An Einzelstandorten wurden Schwermetallgehalte oberhalb der Pruf- und Eingreifwerte fur gartnerisch genutzte Boden (Eikmann und Kloke, 1993) festgestellt. Boden von Hausgarten des Innenstadtgebietes sind durch vergleichsweise hohere Schwermetallgehalte als Kleingartenboden in Stadtrandlage gekennzeichnet. Insgesamt lassen die Rostocker Gartenboden keine gravierenden Belastungen mit den gepruften Schwermetallen erkennen. Heavy metals in garden soils from the urban area of Rostock The contents and mobility of Cd, Cr, Cu, Hg, Ni, Pb and Zn were determined in samples from 32 garden soils in the urban area of Rostock, Northeast Germany to assess possible risks for crop growth and human nutrition. The total contents of the heavy metals were larger in the garden soils than in the agricultural soils of the surrounding countryside. These relative enrichments originated from point sources and diffuse pollution. A number of soils had contents of total and mobile heavy metals above the threshold values for garden soils applied in Germany (Eikmann and Kloke, 1993). Generally, the topsoils had larger contents of the investigated metals than the subsoils. Furthermore, the soils in the centre of the city had metal contents larger than the soils in the outskirts. Generally, there was no large-scale heavy soil pollution with the investigated metals in the garden soils of Rostock. However, several local enrichments indicate the monitoring of heavy metal contents and mobility in garden soils needs to be completed and continued.

Visualization of Colloid Transport Pathways in Mineral Soils Using Titanium(IV) Oxide as a Tracer

In soils, colloidal transport has been identified as the most important pathway for strong adsorbing, environmental contaminants like pesticides, heavy metals, and phosphorus. We conducted a comparative dye tracer experiment using a Brilliant Blue (BB) solution and a Titanium(IV) oxide (TiO) colloid suspension (average particle size 0.3 μm), aiming to visualize and quantify colloid pathways in soils. Both dye tracers showed comparable general flow patterns with preferred transport over the deepest part of the soil profile, independent of clay content. The stained area was generally smaller for TiO than for BB by a factor of ten, however, and there was no TiO to be found at all in the low clay content soil. The travel distance was almost identical for the solution and the suspension (0.7 m) giving evidence that environmentally critical compounds bound to microparticles may be vertically transported over longer distances in soils, even within single rainfall events. The spatial variability of the dye patterns was large on a small scale with a range of 0.35 m for TiO in the horizontal plane, which was taken as a general proof for a pronounced preferential transport situation. The study indicates that TiO is transported exclusively through singular macropores of biogenetic nature, while BB passes also through the soil matrix of coarse-bedded soils, the secondary pore system or interaggregate pore space. The results emphasize the general suitability of TiO for the visualization of colloid transport pathways in soils, opening up new research opportunities for contaminant transport in soils.

Water regime of mechanical—biological pretreated waste materials under fast-growing trees

In this study mechanical—biological pre-treated waste material (MBP) was tested for suitability to serve as an alternative surface layer in combination with fast-growing and water-consumptive trees for final covers at landfill sites. The aim was to quantify evapotranspiration and seepage losses by numerical model simulations for two sites in Germany. In addition, the leaf area index (LAI) of six tree species over the growing season as the driving parameter for transpiration calculations was determined experimentally. The maximum LAI varied between 3.8 and 6.1 m2 m—2 for poplar and willow clones, respectively. The evapotranspiration calculations revealed that the use of MBP waste material for re-cultivation enhanced evapotranspiration by 40 mm year— 1 (10 %) over an 11 year calculation period compared to a standard mineral soil. Between 82% (for LAImax = 3.8) and 87% (for LAImax = 6.1) of the average annual precipitation (506 mm) could be retained from the surface layer assuming eastern German climate conditions, compared with a retention efficiency between 79 and 82% for a mineral soil. Although a MBP layer in conjunction with water-consumptive trees can reduce vertical water losses as compared to mineral substrates, the effect is not sufficient to meet legal regulations.

Orientierende untersuchungen zum einfluss des miscanthusanbaus auf ausgewählte eigenschaften verschiedener böden

In vorliegenden Beitrag werden fur 4 verschiedene Standorte in Deutschland die Bodeneigenschaften unter 4‐ bis 6‐jahrigen Miscanthusbestanden als Grundlage fur ein komplex angelegtes Untersuchungsprogramm vorgestellt und diskutiert. Die Varianten “mit Miscanthus” zeichnen sich durch geringfugig erhohte Humusgehalte gegenuber “ohne Miscanthus” aus, verbunden mit weitreichenden Auswirkungen auf andere relevante Bodenmerkmale. Erkennbar werden Beeinflussungen der Wasserretention, der Porositat und der Lagerungsdichte.

Einfluss von gülle, stroh und gründüngung auf ausgewählte fruchtbarkeitsrelevante eigenschaften eines lehmigen sandbodens

In einem 12jahrigen Feldversuch auf lehmigem Sand wurde der Einflus unterschiedlicher Formen der organischen Dungung (Stroh, Stroh‐ und Grundungung, Gulle) auf ausgewahlte chemische und physikalische Merkmale gepruft. Bei kombinierter Anwendung von Stroh‐ und Grundungung zeigten sich verringerte Dichten und erhohte Porenvolumina. Strohdungung bewirkte eine Zunahme der Wasserretention, besonders des pflanzenverfugbaren Wasseranteils. Hinsichtlich der Kationenaustauschkapazitat als Kriterium fur das Nahrstoffspeicherungs‐ und Transformationsvermogen ergaben sich bei den gepruften organischen Dungern Erhohungen gegenuber der Bezugsvariante. Eine Ursache fur die eingetretenen gunstig zu beurteilenden Veranderungen chemischer und physikalischer Bodeneigenschaften bildet der Anstieg der Ct‐ Gehalte.

Willow stands as an alternative method for the reduction of leachate at contaminated sites — numerical investigations

The commonly used multiple-liner-system of modern top sealings of contaminated sites is expensive and in many cases (minor hazardousness of pollutants), not necessary. As an alternative, we investigated the performance of willow stands as the only measure to reduce percolating soil water and therewith pollutant transport to underlying ground water resources. It is well accepted that willows have a high water demand and may considerably reduce percolation. On the basis of experimentally determined soil physical properties of a landfill site, we performed water balance calculations with the physically based HYDRUS-code and a simple bucket approach.  The 20 yr annual leachate rate for bare soil was calculated to vary from 336 (HYDRUS) to 451 mm yr—1 (bucket-model). Willows were able to reduce the annual leachate to 146 (HYDRUS) and 186 mm yr—1 (bucket-model), indicating their great performance compared to a grass- or beechwood cover. However, legal regulations (TASi) in Germany cannot be met with the proposed method. In minor hazardous cases, official authorities may accept willow stands as an alternative system for protection. Weidenpflanzung als Alternativverfahren zur Reduzierung der Sickerwasserrate auf kontaminierten Standorten Die weitverbreiteten mehrschichtigen Oberflachenabdichtungssys-teme fur Altlasten zur Reduktion von Sickerwasser sind teuer und oftmals nicht erforderlich. In dieser Studie wurde die Leistungsfahigkeit von Weidenanpflanzungen als Alternativverfahren zur Sicherung von Altlasten untersucht. Weiden haben einen betrachtlichen Wasserbedarf und konnen damit zu einer deutlichen Verringerung des perkolierenden Bodenwassers beitragen.  Auf Grundlage experimentell erhobener bodenphysikalischer Kennwerte eines Altstandortes wurden Wasserhaushaltsberechnungen mit dem physikalisch basierten HYDRUS-Ansatz und einem Speicherzellenmodell durchgefuhrt.  Es wurden als derzeitige (unbewachsener Boden) jahrliche Sicker-wasserraten 336 (HYDRUS) bis 451 mm a—1 (Speichermodell) errechnet (20-Jahresmittel). Weiden sind in der Lage, die jahrliche Sickerwasserrate auf bis zu 146 (HYDRUS) bzw. 186 mm a—1 (Speichermodell) zu senken und sind damit leistungsfahiger als Vegetationsdecken aus Gras und Buchen. Trotzdem konnen die Vorgaben der TA Siedlungsabfall mit der vorgeschlagenen Methode nicht erfullt werden. Allerdings konnen bei mindergefahrlichen Standorten — wie in diesem Fall — behordliche Ausnahmeregelungen fur Weidenanpflanzungen erteilt werden.

Grundlagenuntersuchungen zur umweltrelevanz teerhaltiger technogener substrate in stadtböden

In Gefas‐ und Inkubationsversuchen wurde die Wirkung steigender teerhaltiger Zusatze auf das Pflanzenwachstum von Gartenkresse (Lepidium sativum L.) sowie das Abbauverhalten dieses Substrates gepruft. Es zeigte sich eine nachteilige Beeinflussung der Pflanzenentwicklung, deren Ausmas durch die Hohe des Teersubstratzusatzes bestimmt war. Zur Aufklarung des Ursachenkomplexes werden als wesentliche Faktoren fluchtige organische Kohlenwasserstoffe, N‐Immobilisierung und O2‐Mangel, induziert durch die einsetzende starke CO2‐Entwicklung, diskutiert.