Peter Leinweber

The influence of different fertilization practices on concentrations of organic carbon and total nitrogen in particle-size fractions during 34 years of a soil formation experiment in loamy marl

SummaryThe concentrations of organic C and total N in five different particle-size fractions were studied under different mineral and organic fertilizer regimens by examining soil samples from the 34-year-old soil-formation pot experiment Hu 3 in Rostock. The C and N concentrations were generally highest in the clay fraction and decreased in the order medium silt >fine silt >coarse silt and sand. For nearly all years and size fractions the following order was obtained for C and N concentrations under the various fertilizer regimens: Compost >farmyard manure >straw + mineral fertilizer >mineral fertilizer. The various particle-size fractions and fertilizer regimens differed in the development of soil organic matter levels. Consequently, characteristic redistributions were found in the proportions of C and N in the various particle-size fractions, particularly after organic fertilizer was no longer applied (years 20–34). This experimental phase was characterized by decreased organic C and increased total N concentrations, and increased proportions of C and N in the clay-size at the expense of the sand fractions.

Seasonal variations of soil organic matter in a long-term agricultural experiment

Seasonal variations of soil organic matter (SOM) were studied in the unfertilized plot (U) and in the NPK+farmyard manure plot (NPK+FYM) of the 88-year-old ‘Static Experiment’ at Bad Lauchstädt (Germany). Decreases in the C concentrations by 0.24% (U) and 0.43% (NPK+FYM) between June and August were observed which were significant at the p < 0.01 level. The largest differences in N concentrations were 0.035% (U: August vs. September) and 0.029% (NPK+FYM: April vs. May). The C/N ratios were lowest in July and August (∼12).The seasonal variations of SOM contents were reflected in significant differences in the C concentrations of organo-mineral particle-size fractions. The proportions of soil C, associated with clay increased from 56% and 38% in April to 69% and 48% in October in the untreated and NPK+FYM-treated plot, respectively.Pyrolysis-field ionization mass spectra of whole soil samples taken in June and August showed larger differences in the molecular composition of SOM in the untreated plot than in the NPK+FYM plot. On the basis of thermograms for six important compound classes of SOM, seasonal variations in (a) their amounts and (b) their incorporation in thermally different stable humic and/or organo-mineral bonds were visualized. Within four weeks of a net mineralization of SOM, portions of phenols, lignin monomers, lignin dimers, alkylaromatics, lipids, N-containing compounds and carbohydrates reached a higher thermal stability, which can be explained by advanced crosslinking. These results represent the first application of this novel methodology to the subtle and difficult problem of seasonal SOM variations.

Pyrolysis-field ionization mass spectrometry of agricultural soils and humic substances: Effect of cropping systems and influence of the mineral matrix

Whole soil samples, extracted humic substances, the corresponding fulvic (FA) and humic acids (HA) and the extraction residues (humins) from long-term, agricultural test plots were investigated by in-source pyrolysis-field ionization mass spectrometry (Py-FIMS). For the soils distinct differences in the chemical composition of the organic matter in differently managed fields were observed. The FI mass spectra of the extracted humic substances gave complementary chemical information, as they cover a larger mass range compared to the whole soil spectra. The chemical, structural information of the conventional alkaline extraction residues was demonstrated by Py-FIMS spectra to be similar to that of the related soil samples.Influences of mineral matrix to organic matter ratios were studied on mixtures of extracted humic substances with defined mineral components such as quartz, basalt, iron oxide (Fe2O3), Ca-montmorillonite, kaolinite and illite. It was shown that in these mixtures the number of mass signals detected and the covered mass range decreased, when organic carbon concentrations (Corg) in this synthetic mineral matrix dropped below 2% (w/w). Limitations in the direct application of Py-FIMS might arise in the case of natural soil samples with Corg concentrations below 0.5% (w/w), high contents of swelling clay minerals and iron oxides. ei]{gnR}{fnMerckx}

Initial formation of soil organic matter from grass residues in a long-term experiment

SummaryThe formation of soil organic matter from grass residues was studied using samples of a long-term experiment (34 years) on humus and soil formation at Rostock, Germany (Hu 3), by elemental analyses (C and N) and pyrolysis-field ionization mass spectrometry of grass residues, humus-free loamy marl, mixtures of this loamy marl with grass roots, and whole soil samples from the 2nd, 7th, 13th, 19th, 25th, 29th, and 34th year of the experiment. The pyrolysis-field ionization mass spectra of the two grass species Phleum pratense and Lolium multiflorum were similar insofar as signals characteristic of lignin dimers and phytosterols dominated at higher masses and for mono-and polysaccharides at lower masses. The most prominent differences between overand underground plant constituents were indicated by higher relative abundances of lignin dimers in the stems and leaves and of sugars and suberin-derived phytosterols in the roots. In the investigation of the influence of mineral to organic matter ratios, comparatively weak effects of the inorganic matrix were obtained: firstly, in the lower mass range (m/z<250), secondly, for organic matter concentrations between 1.0% and 2.0%, and thirdly, for certain classes of compounds such as phenols, alkanes/alkenes, N heterocycles and mono-and polysaccharides. The qualitative differences in the molecular composition of soil organic matter were clearly attributed to its rapid increase during the first 7 years of the experiment and largely originated from a relative enrichment of lignin dimers. Then, in the period of steady-state soil organic matter levels, dynamic changes were indicated by slight enrichments of mono-and polysaccharides, alkanes/alkenes, fatty acids, N heterocycles, and fluctuating data for phenols/lignin monomers, lignin dimers, and the sum of N compounds. Alkylaromatics showed a steep increase between the 13th and 19th years and remained then on a high level.

Influence of the mineral matrix on the formation and molecular composition of soil organic matter in a long-term, agricultural experiment

The formation of soil organic matter from grass residues was studied in a 34-year-old pot experiment with grass cultivation on loamy marl using pyrolysis-field ionization mass spectrometry (Py-FIMS). For whole soils, the Py-FI mass spectra indicated clear changes in the molecular-chemical composition during SOM formation from grass residues. In particular, the enrichment of heterocyclic N-containing compounds with time was remarkable.For organomineral size fractions, even larger differences in the composition of SOM were found. The changes between the 13th and 34th experimental year are partly explained by a net transfer of phenols, lignin monomers and lignin dimers from medium silt to fine silt. Moreover, it is demonstrated that temperature-resolved Py-FIMS enables the determination of the thermal energy required for the evolution of individual compound classes which is a measure of the strength of humic- and organomineral bonds. At lower temperatures (< 400 °C), the enrichment of thermally less stable and/or loosely bound organic matter with cultivation time in clay and fine silt is due to carbohydrates, N-containing compounds, phenols and lignin monomers. Shifts of evolution maxima toward a higher pyrolysis temperature (> 400 °C) in clay, fine silt and medium silt are explained by a higher thermal stability of humic and/or organomineral bonds of lignin dimers, alkylaromatics and lipids, that developed during the last two decades of the experiment.

Molecular characterization of soil organic matter in Pleistocene moraines from the Bolivian Andes

Abstract The molecular composition of soil organic matter (SOM) in Pleistocene moraines of different ages in the Bolivian Andes was investigated by elemental analyses (C, N) and by off-line pyrolysis under nitrogen at atmospheric pressure and on-line pyrolysis-field ionization mass spectrometry (Py-FIMS) in vacuum. Moraine ages of 9,000, 16,000, 20,000 and > 20,000 years were derived from 14C datings of adjoining hard-cushion moors and were considered as a soil chronosequence. The Py-FI mass spectra of the soil samples were characterized by intensive signals of fatty acids, sterols and suberin-derived molecules. With increasing soil age, (1) relative enrichments of resistant lipids, sterols, suberin constituents, fatty acids and nitrogen-containing compounds and (2) shifts of the volatilization onsets and maxima to higher temperatures in thermograms of total ion intensities and of lipids and fatty acids were observed. These increases in thermal stability indicated the strengthening of chemical bonds as a significant process during SOM aging. It was further concluded that Py-FIMS, complementary to other analytical methods, can be used to monitor molecular-chemical changes of SOM composition and stability in soil chronosequences.

Organo-mineral soil clay fractions in fertilization experiments: mineralogy, amounts and quality of organic matter and influence on soil properties

Abstract The results of our studies on organo-mineral soil clay fractions isolated from long-term fertilization experiments in eastern Germany were compiled. In mineralogical studies it was found that illites were the dominant three-layer minerals in all soil profiles, with the exception of a Dystric Cambisol on gneiss where secondary chlorite is the dominant three-layer mineral. Mineral transformations were observed in unfertilized soils that were observed over a long period and in a soil formation experiment with loamy marl. The investigation of clay-associated organic substances has shown that the organic carbon and total nitrogen concentrations (0.5–10.2% and 0.1–1.2%, respectively) were related to the genetic soil types, to management practices, and to the duration of soil formation processes. This was also true for the quality of organic matter, which was studied by differential thermal analysis (DTA), thermogravimetry (TG) and pyrolysis-field ionization mass spectrometry (Py-FIMS). The latter method enabled the observation of clay-associated organic substances on the basis of molecular subunits. The cation exchange capacities of the clay fractions were closely correlated to the organic carbon concentrations, and therefore dependent on the management practice. Significant correlations were found between the organic matter contents of the clay fractions and physical soil properties such as bulk density and specific gravity, water retention and compressibility. It was concluded that the investigation of the organo-mineral character of soil clay fractions allows a deeper insight into the relationships between organic and inorganic constituents and the properties of soils.