Markus Kleber

Persistence of soil organic matter as an ecosystem property

Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming.

Review of XRD-based quantitative analyses of clay minerals in soils: the suitability of mineral intensity factors

Abstract The determination of the types and relative amounts of the minerals present in soil forms an essential component of most soil characterization efforts. This paper reviews protocols for XRD-based quantitative clay mineral analysis in soils, with emphasis on methods using mineral intensity factors in combination with the so-called 100% approach. We summarize methodological differences and characteristic features and give information about problems, procedural flaws and the comparability of results of some widely distributed procedures. We found that XRD-based protocols are abundant and inconsistent. Procedural flaws exist independent of the quantification approach due to the need of inevitable suppositions and unknown variability in phase chemistry, degree of structural disorder and of interstratification of the soil clay minerals. Quantification protocol instructions using mineral intensity factors in combination with the 100% approach differ in every methodological step. Variance is increased through absent standardization of sample preparation, clay mineral identification or determination of the integrated peak area. Even if the whole quantification process is held constant and precautions are adhered to, results may only be considered as a rough estimate of reality. Quantitative aspects of mineralogical variability within one soil profile and among different soil profiles related by identical parent material may be assessed, if standardized procedures are employed. Different quantification protocols will yield different phase quantities. We are not able to recommend the uncritical use of mineral intensity factors as derived from the literature.

Carbon storage in loess derived surface soils from Central Germany: Influence of mineral phase variables

The influence of the soil mineral phase on organic matter storage was studied in loess derived surface soils of Central Germany. The seven soils were developed to different genetic stages.  The carbon content of the bulk soils ranged from 8.7 to 19.7 g kg—1. Clay mineralogy was confirmed to be constant, with illite contents > 80 %. Both, specific surface area (SSA, BET-N2-method) and cation exchange capacity (CEC) of bulk soils after carbon removal were better predictors of carbon content than clay content or dithionite-extractable iron. SSA explained 55 % and CEC 54 % of the variation in carbon content. The carbon loadings of the soils were between 0.57 and 1.06 mg C m—2, and therefore in the ”monolayer equivalent” (ME) level. The increase in SSA after carbon removal (ΔSSA) was significantly and positively related to carbon content (r2 = 0.77). Together with CEC of carbon-free samples, ΔSSA explained 90 % of the variation in carbon content.  Clay (< 2 μm) and fine silt fractions (2—6.3 μm) contained 68—82 % of the bulk soil organic carbon. A significantly positive relationship between carbon content in the clay fraction and in the bulk soil was observed (r2 = 0.95). The carbon pools of the clay and fine silt fractions were characterized by differences in C/N ratio, δ13C ratio, and enrichment factors for carbon and nitrogen. Organic matter in clay fractions seems to be more altered by microbes than organic matter in fine silt fractions.  The results imply that organic matter accumulates in the fractions of smallest size and highest surface area, apparently intimately associated with the mineral phase. The amount of cations adhering to the mineral surface and the size of a certain and specific part of the surface area (ΔSSA) are the mineral phase properties which affect the content of the organic carbon in loess derived arable surface soils in Central Germany most. There is no monolayer of organic matter on the soil surfaces even if carbon loadings are in the ME level. Kohlenstoffspeicherung in mitteldeutschen Oberboden aus Los: Einfluss der Mineralphase In Oberboden mitteldeutscher Ackerstandorte wurde der Einfluss der Bodenmineralphase auf die Speicherung von organischer Substanz untersucht. Die sieben aus Los entstandenen Boden waren genetisch unterschiedlich weit entwickelt.  Der Kohlenstoffgehalt der Oberboden erreichte Werte von 8,7 bis 19,7 g kg—1. Die Tonmineralogie war in allen Boden gleich mit Illitgehalten von > 80 %. Sowohl die spezifische Oberflache (SSA, BET-N2-Methode) als auch die Kationenaustauschkapazitat (CEC) der Boden nach Kohlenstoffentfernung waren geeignetere Variablen zur Vorhersage des Kohlenstoffgehaltes als der Tongehalt oder das Dithionit-extrahierbare Eisen. Durch die SSA war in der Lage, 55 % der Variabilitat des Kohlenstoffgehaltes wurden erklart, durch die CEC 54 %. Die Belegung der Oberflache mit Kohlenstoff erreichte Werte zwischen 0,57 und 1,06 mg C m—2 und lag somit im Bereich der „monolayer aquivalenten“ (ME) Belegung. Die Beziehung zwischen dem Kohlenstoffgehalt und der Zunahme der spezifischen Oberflache durch die Entfernung der organischen Substanz (ΔSSA) war signifikant positiv (r2 = 0,77). Zusammen mit der CEC der Proben nach Kohlenstoffentfernung erklarte ΔSSA 90 % der Variabilitat des Kohlenstoffgehaltes.  Die Ton- (< 2 μm) und Feinschluff-Fraktionen (2—6,3 μm) der Boden enthielten 68—82 % des organischen Kohlenstoffs. Zwischen den Kohlenstoffgehalten der Tonfraktion und des Feinbodens wurde eine signifikant positive Beziehung beobachtet (r2 = 0,95). Die organische Substanz in der Ton- und Feinschluff-Fraktion war durch unterschiedliche C/N-Verhaltnisse, δ13C-Werte und Anreicherungsfaktoren fur Kohlenstoff und Stickstoff gekennzeichnet. Die organische Substanz in der Tonfraktion scheint im Vergleich zur Feinschluff-Fraktion starker umgesetzt zu sein.  Die Ergebnisse deuten daraufhin, dass sich organische Substanz in den Fraktionen mit der kleinsten Partikelgrose und der hochsten Oberflache anreichert und dabei scheinbar intensiv mit der Mineralphase assoziiert ist. Der Gehalt an organischem Kohlenstoff in mitteldeutschen Ackeroberboden aus Los wird in Bezug auf die Mineralphase vor allem durch (1) die Menge der Kationen an der Mineraloberflache und (2) die Grose eines spezifischen Anteils der Oberflache (ΔSSA) beeinflusst. Die Kohlenstoffbelegung der Oberflache entspricht keiner „Monolayer“-Belegung.

Ion exchange resin-soil mixtures as a tool in net nitrogen mineralisation studies

Mixed-bed ion exchange resins (IER) were mixed with intact soil aggregates and incubated at 60% water filled pore space in closed polyethylene bags for 12 weeks. To test IER eAects on N losses, nitrification and net N mineralisation, an arable soil and a grassland soil, diAering in organic matter content, were chosen and two crop residues (wheat straw, sugar-beet leaves) with diAerent C-to-N ratios were added to the arable soil. It was proposed that IER might exert an influence on N cycling similar to that of plant roots. Nitrification was inhibited by adsorption of NH4 in the +IER treatments. Net N mineralisation was greater in the grassland soil than in the arable soil which had less soil organic matter. Without incorporation of additional organic substrates, net N mineralisation was not aAected by IER in both soils. Straw addition to the arable soil caused immediate N

Construction and Evaluation of Redox Electrode with Summing Operational Amplifier: Application in Study of Methane Emission

Measurements of redox potential (Eh) provide qualitative information about oxidation–reduction conditions in hydromorphic soils. However, these measurements are confounded by several theoretical and technical complications. One seldom-discussed problem is interferences in consequence of static, capacitive or inductive coupling of stray fields (noise). This study developed an “active” redox electrode, which is immune against ambient noise coupling on the transmission line. An integrated voltage follower included into the electrode body was used to decouple the sensitive high impedance primary circuit from all further devices of the signal chain. The electrode design was field-tested over four months. Trends of Eh on 12 electrodes of this design in a Fluvaquentic Humaquept are presented and discussed in relationship with changing of boundary conditions (precipitation, groundwater level) and emission of methane.

Rekultivierung von Bergehalden des Steinkohlebergbaus — Bodenkundliche Untersuchungen am Versuchsstandort Halde Reden

Der Steinkohlebergbau hat eine Vielzahl devastierter Flachen geschaffen, die in ihrer gegenwartigen Gestalt ihre ursprunglichen naturraumlichen Funktionen nicht mehr erfullen konnen. Sofem nicht Kontamination durch Xenobiotika vorliegt, ist die Abwesenheit eines entwickelten Oberbodens das wichtigste Hindernis fur eine Wiederbesiedlung durch die Vegetation. Dieser Oberboden soll aus einem strukturierten, belebten Gemisch mineralischer und organischer Substanz bestehen und Wasser, Nahrstoffe sowie Lebensraum fur Pflanzen, Tiere und Mikroorganismen bereitstellen. Der naheliegende Ausweg, humusreichen Oberboden auf solche Flachen zu importieren, bedeutet den Abtrag eben diese s Oberbodens an anderer Stelle und erneut devastierte Flachen.