Dissertationen
https://kobra.uni-kassel.de:443/handle/123456789/2010042732709
2024-03-19T07:27:20ZRobustness of portable and laboratory-based visible/near- and mid-infrared spectroscopy for optimized determination of temporally and spatially variable soil properties
https://kobra.uni-kassel.de:443/handle/123456789/13550
Application of visible/near- (VISNIRS) and mid-infrared (MIRS) spectroscopy to the field of soil science is promising, as it allows information about a range of properties to be collected simultaneously and rapidly, thereby providing high spatial and temporal resolution data for use in, e.g., soil mapping, precision agriculture, and long-term monitoring. However, investigation of the conditions under which visNIRS and MIRS can replace traditional lab methods is required, as the accuracy, robustness, and efficiency of these methods depend on a wide range of factors that are not sufficiently understood. The objective of this dissertation was therefore to i) compare the performance of field vs lab visNIRS and MIRS for prediction of key soil properties using partial least squares regression; ii) investigate the spectral prediction mechanisms for these soil properties using a) loadings of PLSR components, b) variable importance in the projection scores, c) principal component analysis, and d) model robustness in independent validation; iii) determine the effects of disturbance factors, including a) soil moisture (and its interaction with soil texture) and b) changes in the crop residue quantity (via residue incorporation or decomposition) and quality (clover vs wheat straw incorporation) in soil; iv) compare the performance of various sizes of local calibrations and regional calibrations with and without the addition of local soils (spiking); v) compare the accuracy of spectral models for prediction of soil organic carbon (OC) fractions of variable residence time to prediction with covariates using multiple linear regressions; and vi) determine if spectroscopy can accurately predict the effects of tillage treatments on soil OC contents using analysis of variance. The three studies composing this dissertation utilized surface soils from several sites in Germany. The soil properties under investigation included total and fraction OC contents, total nitrogen (TN) content, pH, and texture. These studies demonstrated the excellent accuracy of lab MIRS OC and TN estimations, while the accuracy of visNIRS and MIRS was lower and more comparable for texture predictions. We found spectral estimation of OC fractions may not have an advantage compared to estimation with covariates since prediction mechanisms are likewise partially indirect (i.e. both organic and mineral spectral signatures were important). The loss of prediction accuracy from lab to field measurement was greater for MIRS than visNIRS, but in situ performance rankings of visNIRS vs MIRS were moisture dependent. Soil moisture more negatively affected OC prediction than clay prediction. No simple trend was established for the performances of soil subsets with low, high or variable moisture content, but accuracy was most negatively affected by moisture for the site with the highest sand content. The independence of the validation soils had a marked effect on model performance, and calculation of bias was essential to describing calibration suitability and hinted at indirect prediction mechanisms. We demonstrated the performance of lab vs field MIRS models for small local and regional calibrations with and without spiking, and the diminishing marginal returns to accuracy from using ever-larger calibration sets. While purely regional lab-MIRS models could accurately predict changes to OC content in response to tillage, field-MIRS models required local or spiked regional calibration to achieve accurate estimations. Thus, the higher efficiency of field measurement is counterbalanced by a more arduous calibration process to achieve satisfactory models.; Die Anwendung der Spektroskopie im sichtbaren/nahen- (visNIRS) und mittleren (MIRS) Infrarotbereich auf dem Gebiet der Bodenkunde ist vielversprechend, da sie die gleichzeitige und schnelle Erfassung von Informationen über eine Reihe von Eigenschaften ermöglicht und dadurch Daten mit hoher räumlicher und zeitlicher Auflösung liefert, die z. B. für die Bodenkartierung, die Präzisionslandwirtschaft und das Bodenmonitoring verwendet werden können. Es muss jedoch untersucht werden, unter welchen Bedingungen visNIRS und MIRS traditionelle Labormethoden ersetzen können, da die Genauigkeit, Robustheit und Effizienz dieser Methoden von einer Vielzahl von Faktoren abhängt, die nicht ausreichend bekannt sind. Ziel dieser Dissertation war es daher, i) die Leistung von visNIRS und MIRS im Feld und im Labor bei der Vorhersage wichtiger Bodeneigenschaften mit Hilfe der partiellen Kleinstquadratregression zu vergleichen; ii) die spektralen Vorhersagemechanismen für diese Bodeneigenschaften anhand von a) Ladungen der PLSR-Komponenten, b) der Variablenbedeutung in den Projektionsergebnissen, c) der Hauptkomponentenanalyse und d) der Modellrobustheit in der unabhängigen Validierung zu untersuchen; iii) die Bestimmung der Auswirkungen von Störfaktoren, einschließlich der Bodenfeuchtigkeit (und ihrer Wechselwirkung mit der Bodentextur) und der Veränderungen der Menge an Ernterückständen (durch Einarbeitung oder Zersetzung) und der Qualität (Einarbeitung von Klee oder Weizenstroh) im Boden; iv) der Vergleich der Leistung verschiedener Größen von lokalen Kalibrierungen und regionaler Kalibrierungen mit und ohne Zugabe lokaler Böden ("Spiking"); v) der Vergleich der Genauigkeit von Spektralmodellen für die Vorhersage von Anteilen organischen Kohlenstoffs (OC) im Boden bei variabler Verweilzeit mit der Vorhersage mit Kovariaten unter Verwendung multipler linearer Regressionen; und vi) die Bestimmung, ob die Spektroskopie die Auswirkungen von Bodenbearbeitungsmaßnahmen auf den OC-Gehalt im Boden unter Verwendung von Varianzanalysen genau vorhersagen kann. In den drei Studien, aus denen sich diese Dissertation zusammensetzt, wurden Oberböden von verschiedenen Standorten in Deutschland verwendet. Zu den untersuchten Bodeneigenschaften gehörten der Gesamt- und Fraktions-OC-Gehalt, der Gesamtstickstoffgehalt (TN), der pH-Wert und die Textur. Diese Studien zeigten die hervorragende Genauigkeit der OC- und TN-Schätzungen mit MIRS im Labor, während die Genauigkeit von visNIRS und MIRS bei der Vorhersage der Textur geringer war und eher vergleichbar. Wir fanden heraus, dass die spektrale Schätzung von OC-Anteilen im Vergleich zur Schätzung mit Kovariaten möglicherweise keinen Vorteil bietet, da die Vorhersagemechanismen ebenfalls teilweise indirekt sind (d. h. sowohl organische als auch mineralische Spektralsignaturen waren wichtig). Der Verlust an Vorhersagegenauigkeit von der Labor- zur Feldmessung war bei MIRS größer als bei visNIRS, aber die Einstufung der In-situ-Leistung von visNIRS gegenüber MIRS war feuchteabhängig. Die Bodenfeuchtigkeit wirkte sich negativer auf die OC-Vorhersage aus als auf die Tonvorhersage. Für die Leistungen von Bodenuntergruppen mit niedrigem, hohem oder variablem Feuchtigkeitsgehalt wurde kein einfacher Trend festgestellt, aber die Genauigkeit wurde am stärksten durch die Feuchtigkeit für den Standort mit dem höchsten Sandgehalt beeinträchtigt. Die Unabhängigkeit der Validierungsböden hatte eine deutliche Auswirkung auf die Modellleistung, und die Berechnung der Verzerrung war für die Beschreibung der Kalibrierungseignung von wesentlicher Bedeutung und gab Hinweise auf indirekte Vorhersagemechanismen. Wir demonstrierten die Leistung von Labor- und Feld-MIRS-Modellen für kleine lokale und regionale Kalibrierungen mit und ohne "Spiking" sowie die abnehmenden Grenzerträge zur Genauigkeit bei Verwendung immer größerer Kalibrierungssätze. Während rein regionale Labor-MIRS-Modelle Änderungen des OC-Gehalts als Reaktion auf die Bodenbearbeitung akkurat vorhersagen konnten, benötigten Feld-MIRS-Modelle eine lokale oder regionale Kalibrierung mit "Spiking", um genaue Schätzungen zu erhalten. Die höhere Effizienz von Feldmessungen wird also durch einen mühsameren Kalibrierungsprozess ausgeglichen, um zufriedenstellende Modelle zu erhalten.
2021-01-01T00:00:00ZGreenberg, IsabelApplication of visible/near- (VISNIRS) and mid-infrared (MIRS) spectroscopy to the field of soil science is promising, as it allows information about a range of properties to be collected simultaneously and rapidly, thereby providing high spatial and temporal resolution data for use in, e.g., soil mapping, precision agriculture, and long-term monitoring. However, investigation of the conditions under which visNIRS and MIRS can replace traditional lab methods is required, as the accuracy, robustness, and efficiency of these methods depend on a wide range of factors that are not sufficiently understood. The objective of this dissertation was therefore to i) compare the performance of field vs lab visNIRS and MIRS for prediction of key soil properties using partial least squares regression; ii) investigate the spectral prediction mechanisms for these soil properties using a) loadings of PLSR components, b) variable importance in the projection scores, c) principal component analysis, and d) model robustness in independent validation; iii) determine the effects of disturbance factors, including a) soil moisture (and its interaction with soil texture) and b) changes in the crop residue quantity (via residue incorporation or decomposition) and quality (clover vs wheat straw incorporation) in soil; iv) compare the performance of various sizes of local calibrations and regional calibrations with and without the addition of local soils (spiking); v) compare the accuracy of spectral models for prediction of soil organic carbon (OC) fractions of variable residence time to prediction with covariates using multiple linear regressions; and vi) determine if spectroscopy can accurately predict the effects of tillage treatments on soil OC contents using analysis of variance. The three studies composing this dissertation utilized surface soils from several sites in Germany. The soil properties under investigation included total and fraction OC contents, total nitrogen (TN) content, pH, and texture. These studies demonstrated the excellent accuracy of lab MIRS OC and TN estimations, while the accuracy of visNIRS and MIRS was lower and more comparable for texture predictions. We found spectral estimation of OC fractions may not have an advantage compared to estimation with covariates since prediction mechanisms are likewise partially indirect (i.e. both organic and mineral spectral signatures were important). The loss of prediction accuracy from lab to field measurement was greater for MIRS than visNIRS, but in situ performance rankings of visNIRS vs MIRS were moisture dependent. Soil moisture more negatively affected OC prediction than clay prediction. No simple trend was established for the performances of soil subsets with low, high or variable moisture content, but accuracy was most negatively affected by moisture for the site with the highest sand content. The independence of the validation soils had a marked effect on model performance, and calculation of bias was essential to describing calibration suitability and hinted at indirect prediction mechanisms. We demonstrated the performance of lab vs field MIRS models for small local and regional calibrations with and without spiking, and the diminishing marginal returns to accuracy from using ever-larger calibration sets. While purely regional lab-MIRS models could accurately predict changes to OC content in response to tillage, field-MIRS models required local or spiked regional calibration to achieve accurate estimations. Thus, the higher efficiency of field measurement is counterbalanced by a more arduous calibration process to achieve satisfactory models.
Die Anwendung der Spektroskopie im sichtbaren/nahen- (visNIRS) und mittleren (MIRS) Infrarotbereich auf dem Gebiet der Bodenkunde ist vielversprechend, da sie die gleichzeitige und schnelle Erfassung von Informationen über eine Reihe von Eigenschaften ermöglicht und dadurch Daten mit hoher räumlicher und zeitlicher Auflösung liefert, die z. B. für die Bodenkartierung, die Präzisionslandwirtschaft und das Bodenmonitoring verwendet werden können. Es muss jedoch untersucht werden, unter welchen Bedingungen visNIRS und MIRS traditionelle Labormethoden ersetzen können, da die Genauigkeit, Robustheit und Effizienz dieser Methoden von einer Vielzahl von Faktoren abhängt, die nicht ausreichend bekannt sind. Ziel dieser Dissertation war es daher, i) die Leistung von visNIRS und MIRS im Feld und im Labor bei der Vorhersage wichtiger Bodeneigenschaften mit Hilfe der partiellen Kleinstquadratregression zu vergleichen; ii) die spektralen Vorhersagemechanismen für diese Bodeneigenschaften anhand von a) Ladungen der PLSR-Komponenten, b) der Variablenbedeutung in den Projektionsergebnissen, c) der Hauptkomponentenanalyse und d) der Modellrobustheit in der unabhängigen Validierung zu untersuchen; iii) die Bestimmung der Auswirkungen von Störfaktoren, einschließlich der Bodenfeuchtigkeit (und ihrer Wechselwirkung mit der Bodentextur) und der Veränderungen der Menge an Ernterückständen (durch Einarbeitung oder Zersetzung) und der Qualität (Einarbeitung von Klee oder Weizenstroh) im Boden; iv) der Vergleich der Leistung verschiedener Größen von lokalen Kalibrierungen und regionaler Kalibrierungen mit und ohne Zugabe lokaler Böden ("Spiking"); v) der Vergleich der Genauigkeit von Spektralmodellen für die Vorhersage von Anteilen organischen Kohlenstoffs (OC) im Boden bei variabler Verweilzeit mit der Vorhersage mit Kovariaten unter Verwendung multipler linearer Regressionen; und vi) die Bestimmung, ob die Spektroskopie die Auswirkungen von Bodenbearbeitungsmaßnahmen auf den OC-Gehalt im Boden unter Verwendung von Varianzanalysen genau vorhersagen kann. In den drei Studien, aus denen sich diese Dissertation zusammensetzt, wurden Oberböden von verschiedenen Standorten in Deutschland verwendet. Zu den untersuchten Bodeneigenschaften gehörten der Gesamt- und Fraktions-OC-Gehalt, der Gesamtstickstoffgehalt (TN), der pH-Wert und die Textur. Diese Studien zeigten die hervorragende Genauigkeit der OC- und TN-Schätzungen mit MIRS im Labor, während die Genauigkeit von visNIRS und MIRS bei der Vorhersage der Textur geringer war und eher vergleichbar. Wir fanden heraus, dass die spektrale Schätzung von OC-Anteilen im Vergleich zur Schätzung mit Kovariaten möglicherweise keinen Vorteil bietet, da die Vorhersagemechanismen ebenfalls teilweise indirekt sind (d. h. sowohl organische als auch mineralische Spektralsignaturen waren wichtig). Der Verlust an Vorhersagegenauigkeit von der Labor- zur Feldmessung war bei MIRS größer als bei visNIRS, aber die Einstufung der In-situ-Leistung von visNIRS gegenüber MIRS war feuchteabhängig. Die Bodenfeuchtigkeit wirkte sich negativer auf die OC-Vorhersage aus als auf die Tonvorhersage. Für die Leistungen von Bodenuntergruppen mit niedrigem, hohem oder variablem Feuchtigkeitsgehalt wurde kein einfacher Trend festgestellt, aber die Genauigkeit wurde am stärksten durch die Feuchtigkeit für den Standort mit dem höchsten Sandgehalt beeinträchtigt. Die Unabhängigkeit der Validierungsböden hatte eine deutliche Auswirkung auf die Modellleistung, und die Berechnung der Verzerrung war für die Beschreibung der Kalibrierungseignung von wesentlicher Bedeutung und gab Hinweise auf indirekte Vorhersagemechanismen. Wir demonstrierten die Leistung von Labor- und Feld-MIRS-Modellen für kleine lokale und regionale Kalibrierungen mit und ohne "Spiking" sowie die abnehmenden Grenzerträge zur Genauigkeit bei Verwendung immer größerer Kalibrierungssätze. Während rein regionale Labor-MIRS-Modelle Änderungen des OC-Gehalts als Reaktion auf die Bodenbearbeitung akkurat vorhersagen konnten, benötigten Feld-MIRS-Modelle eine lokale oder regionale Kalibrierung mit "Spiking", um genaue Schätzungen zu erhalten. Die höhere Effizienz von Feldmessungen wird also durch einen mühsameren Kalibrierungsprozess ausgeglichen, um zufriedenstellende Modelle zu erhalten.Effects of grassland management intensification on dynamics of soil organic carbon and nitrogen in temperate grassland soils
https://kobra.uni-kassel.de:443/handle/123456789/2018050955472
In Germany, about one third of the agricultural area is managed as permanent grassland. The predominant use of permanent grassland in Germany is mostly the production of fodder for meat or milk production, achieved by grazing or mowing. In addition, an increased demand for biomass to produce renewable energy has influenced grassland management in the last decade. Until 2013, a continuous decrease in grassland due to grassland conversion was recorded (from 2003 to 2013, by a total of about 5 %). The reduction in permanent grassland was accompanied by an increase in intensification of grassland in many places. Therefore, the intensification of grassland management is typically conducted via higher grazing pressure or increased average use by mowing, combined with the application of fertilizers or an increase in fertilizer delivery.
However, especially for farming in naturally small-scale, mountainous landscapes with less productive soils, extensive grazing is recommended for coincidently achieving meat and milk production as well as biodiversity goals.
Also of interest is the renewal of grassland that is entirely or partially carried out, especially in intensively-used grassland, to improve efficiency. Grassland renewal can be performed with or without subsequent tillage.
It is generally known that management intensification of grassland, grassland renewal, or conversion to arable land influences carbon and nitrogen stocks and dynamics in soil.
From these current circumstances, the following objectives have been deduced for my doctoral thesis:
(I) to evaluate the impact of different extensive grazing pressures on carbon and nitrogen in soil, on the coupling of carbon and nitrogen in soil, on soil microbial carbon, on the basal respiration of soil, and on mineral nitrogen in soil.
(II) to evaluate the impact of varying, frequent mowing in combination with and without mineral N fertilization on carbon and nitrogen in soil, on the coupling of carbon and nitrogen in soil, on soil microbial carbon, on ergosterol as a marker of fungal biomass, on soil aggregate size class distribution and its carbon contents, and on the composition of soil organic matter.
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Summary
(III) to investigate the temporal dynamics during grassland renewal from the chemical destruction of the existing vegetation and reseeding either by direct seeding or by prior tillage, and to investigate their effects on organic carbon and nitrogen in soil, on soil microbial carbon, on soil aggregate size class distribution, and on their carbon contents.
For the processing of (I), soil samples were taken during a long-term grazing experiment northwest of Göttingen (FOR BIOdiversity BENefit trial in Solling, Relliehausen), from three different extensively-grazed treatments in three soil depths (0-10 cm, 10-25 cm, and 25-40 cm) in April 2013. The different grazing pressures were determined by measuring the compressed pasture height during the vegetation period, using a rising-plate meter and subsequently adjusting the stocking rate.
The soil samples were analyzed for soil organic carbon (SOC) and nitrogen (Nt) contents, the coupling of carbon and nitrogen, soil microbial carbon (Cmic), basal respiration, and mineral nitrogen (Nmin). Furthermore, pH, clay content, oxalate soluble aluminum, and iron contents were determined. Before data analysis, weighted means were calculated for the stocks of SOC, Nt, Nmin, and Cmic concentrations and basal respiration rates with the proportion of each compressed pasture height class as a weighting factor. A two-factorial analysis of variance (ANOVA) with the factor grazing intensity and the factor block was used in case of normality of residuals and homoscedasticity; otherwise, a Welch ANOVA was used. The weighted stocks of SOC, Nt, Cmic, and basal respiration were not significantly affected (p ≤ 0.05) by grazing intensity.
The data were highly heterogeneous, which was probably caused by the heterogeneous soil mineralogy as well as by uncertainties in the analytical determination of the respective contents, the determination of bulk densities, and the stone contents. Thus, a large part of the variation of the organic carbon and total nitrogen contents can be explained regarding the content of oxalate soluble iron (multiple linear regression: R2 = 0.64). However, the contents of microbial carbon (R2 = 0.96) and the basal respiration rate (R2 = 0.9) are, in turn, explained to a significant extent by the organic carbon contents. Furthermore the possible effects of grazing intensity on the SOC and Nt stocks are presumably explained by the mineralogical variability. However, the low variability of the C/N ratios of different grazing intensities is attributed to a coupling of C and N and, in turn, suggests sufficient SOC and Nt supply in the extensive FORBIOBEN grazing trial.
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Summary
For the processing of (II), soil samples were taken in three soil depths up to 60 cm in depth in a grassland trial near Kiel managed by the Christian Albrechts University of Kiel. The grassland was established uniformly in 2004 after its preceding management as arable land. The trial was established in a randomized block design with three replicates and included these treatments: three cuts (3C) and five cuts (5C) per year; with and without N fertilization (N fertilization: 360 kg N ha-1 year-1 as calcium ammonium nitrate). The soil samples were analyzed for SOC and Nt stocks, Cmic and ergosterol as a marker for fungal biomass, soil aggregate size class distribution, their carbon contents, and the composition of soil organic matter (SOM). Three factorial ANOVAs with the factors cut (levels: 3 cuts and 5 cuts), fertilization (levels: N fertilization and no N fertilization), interaction between cut and fertilization, and factor block (three replicates organized in blocks) were conducted.
The SOC stocks from the 5C regime compared to the 3C regimes in soil depths of 0 ~ 10 cm were significantly higher. This was presumably caused by higher harvesting frequencies, which promote the growth of tiller and leaf, are high in photosynthesis, and can stimulate biomass production. Additionally, the SOC stocks were significantly higher in the treatment without N fertilization in a soil depth of 0 ~ 10 cm. N fertilization may result in a decrease of SOC stocks by increasing microbial activity and altering the C substrate utilization pattern through changes in plant biomass composition. Furthermore, higher biomass yields under the 3C compared to the 5C regime as well as different plant species compositions in the treatments may have also contributed to SOM dynamics. Plant species composition was mainly influenced by the differing cut and fertilization regime. The main plant species under the 5C regime without N fertilization at the time of soil sampling were Lolium perenne and Trifolium repens (a highly productive grass and a legume, respectively). A dense root growth in Lolium perenne in a soil depth of 0 ~ 10 cm and the positive effects of legumes on SOC sequestration presumably caused the increase of the SOC stock under the 5C regime without N fertilization. The Nt stocks were significantly higher under the 5C regime in a depth of 0 ~ 10 cm in comparison to the 3C regime, which is presumably related to the occurrence of Lolium perenne under the 5C regime.
Soil microbial C contents were significantly higher under the 5C regime than under the 3C regime, whereas N fertilization in significantly lower Cmic contents resulted in topsoil. This is presumably related to stimulated root exudation due to a higher harvesting frequency and complex changes in microbial competition and community structure due to the addition of N. Ergosterol contents in the surface soil were significantly higher under the 5C regime in comparison with the 3C regime, presumably caused by different root
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Summary
growth, exudation, and substrate quality. Cmic and the ergosterol contents were closely correlated to SOC stocks (Cmic: Spearman Rs = 0.81; ergosterol: Spearman Rs = 0.87) in topsoil. This indicates that, in the treatments that most likely resulted in higher root productions due to stimulation and plant species composition, microbial and fungal biomasses were stimulated.
For the aggregate distribution in the topsoil layer, a shift from small (250-1000 μm) to large (> 2000 μm) macroaggregates from the 3C to the 5C regime was detected, presumably caused by a higher concentration of roots and root exudates related to Lolium perenne, with its high amount of fine roots under the 5C treatment in a soil depth of 0-10 cm. Five cuts per year affects SOC and Nt stocks positively, as well as contents of large macro-aggregates, Cmic, and ergosterol, which indicate positive effects on the soil fertility of 5C in comparison with 3C.
The N fertilization resulted in slightly negative effects on SOC stocks and Cmic contents. However, as the plant species composition was strongly influenced by cut and fertilization, it is not possible to assign the results found to direct effects (e.g., stimulation of biomass production and root exudation) or to indirect effects due to a different plant species composition.
For the processing of (III) a grassland trial was established on a continuous cut grassland located in Oldenburg in 2013. The trial was managed and supervised by the Chamber of Agriculture of Lower Saxony and the Thünen Institute. In June 2013, a field trial was established and the treatments were arranged in a randomized complete block design with three replicates and consist of
• Treatment (i), chem: chemical sward killing with glyphosate, followed by direct seeding of grassland in 1-cm depth;
• Treatment (ii), phys: chemical sward killing with glyphosate followed by the use of a rotary cultivator, a moldboard plow (25-cm deep), and a land packer, afterwards seeding of grassland;
• Treatment (iii), continuous cut grassland as control.
Soil samples were taken five times during August 2013 to October 2014, each replicated four times in three soil depths. SOC stocks, aggregate size classes, and organic carbon stored in aggregate size classes were analyzed using two-way analysis of variance
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Summary
with the factors grassland renovation (control, chem, and phys) and block (blocks 1 to 3). For further data analysis, Spearman ́s rank correlation and regression analysis was conducted.
Soil carbon stocks showed no significant differences between the grassland renewal with or without plowing and control. This suggests that a grassland renovation, after neither a purely chemical destruction of sward nor a grassland renovation using a plow, had a direct impact on the loss of carbon stocks in the grassland soils. This is perhaps related to the rather low pH in the soil (on average, 4.8), resulting in hampered microbial biomass, which, in turn, hampered the degradation of organic material.
However, grassland renewal after plowing leads to an increase in microaggregate concentrations six days after plowing, compared to the grassland control in the surface soil and in the soil profile. This indicates that one-time plowing had a direct impact on soil aggregates and destroyed macroaggregates, which fragmented into microaggregates.
However, significant seasonal variations of macro- and microaggregate concentrations over time were visible. Higher macroaggregate concentrations were found during periods with increased rainfall following higher gravimetric water content in the soil, compared to periods with less rainfall and less gravimetric water content. Correlation analysis and multiple linear regression analysis have shown that the gravimetric soil water content had a putatively major influence on the distribution of aggregate size classes. Thus, lower gravimetric soil water content led to a higher concentration of microaggregates and a lower concentration of macroaggregates, while higher gravimetric soil water content led to lower microaggregate and higher macroaggregate concentrations.
The physical renovation two and seven months after plowing also led to a significantly higher microaggregate concentration in the surface soil compared to the grassland renewal without plowing, while the concentrations in the permanent grassland were in between. In the chemical renovation, the larger roots of the dead plants might still be largely undecomposed, protecting macroaggregates from degeneration. In the physical renovation, plowing affects macroaggregates negatively by dismantling them into microaggregates via mechanical forces. Furthermore, dead roots were rearranged and breached, which caused a loss of stability in the soil matrix. However, a year after plowing and grassland renovation, no significant difference existed compared to the other treatments. In the beginning, no effect of grassland renovation on SOC in aggregates was visible. However, later microaggregates become more important than macroaggregates in the sequestration of SOC compared to the unplowed control. Because of the late response in SOC in
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Summary
aggregates after the plowing event, it seems that the indirect effects (for instance, the degradation of the root systems of the dead plants) on soil aggregates had a wider influence than the direct physical impact of the plow. The plowing event in the physical renovation caused direct physical destruction of the aggregates and, indirectly, destruction of the root systems of the dead plants. However, impacts on soil macroaggregates were nullified one year after grassland renovation.
Chemical renovation resulted in higher macroaggregate concentrations compared with the physical renovation, especially two-to-seven months after the renovation, and in similar concentrations compared with the permanent grassland in any sampling time within one year. Presumably, dead plant roots could act as binding agents and stabilize aggregates for some time. The high temporal variation in the aggregate distribution within one year in the renovated as well as in the permanent grassland indicates that the soil moisture had a wide influence and that dry conditions in the soil led to a breakdown of larger aggregates.
From the findings obtained above, it can be concluded that the impact of the intensified use of grassland on carbon and nitrogen dynamics is highly dependent on location. First, in the implementation and the degree of intensification, major differences have been observed. Thus, a direct comparison are not directly achievable. However, it can be stated that intensified grassland management, except with a high application rate of mineral N fertilizer and a large removal of biomass (with a mean of 1459 g m-2), does not or only has a low tendency to have negative impacts on the SOC and Nt stocks and sequestration mechanisms. Unlike the loss of biodiversity through intensified use, the SOC stocks and sequestration mechanisms, which are inevitably linked to plant species diversity and the variety of soil organisms, tend to react more slowly to management changes, while showing relatively rapid regeneration. Thus, targeted and appropriate management seems to be important when favoring SOC stocks and sequestration mechanisms.
2018-05-09T00:00:00ZNüsse, Anja MarieIn Germany, about one third of the agricultural area is managed as permanent grassland. The predominant use of permanent grassland in Germany is mostly the production of fodder for meat or milk production, achieved by grazing or mowing. In addition, an increased demand for biomass to produce renewable energy has influenced grassland management in the last decade. Until 2013, a continuous decrease in grassland due to grassland conversion was recorded (from 2003 to 2013, by a total of about 5 %). The reduction in permanent grassland was accompanied by an increase in intensification of grassland in many places. Therefore, the intensification of grassland management is typically conducted via higher grazing pressure or increased average use by mowing, combined with the application of fertilizers or an increase in fertilizer delivery.
However, especially for farming in naturally small-scale, mountainous landscapes with less productive soils, extensive grazing is recommended for coincidently achieving meat and milk production as well as biodiversity goals.
Also of interest is the renewal of grassland that is entirely or partially carried out, especially in intensively-used grassland, to improve efficiency. Grassland renewal can be performed with or without subsequent tillage.
It is generally known that management intensification of grassland, grassland renewal, or conversion to arable land influences carbon and nitrogen stocks and dynamics in soil.
From these current circumstances, the following objectives have been deduced for my doctoral thesis:
(I) to evaluate the impact of different extensive grazing pressures on carbon and nitrogen in soil, on the coupling of carbon and nitrogen in soil, on soil microbial carbon, on the basal respiration of soil, and on mineral nitrogen in soil.
(II) to evaluate the impact of varying, frequent mowing in combination with and without mineral N fertilization on carbon and nitrogen in soil, on the coupling of carbon and nitrogen in soil, on soil microbial carbon, on ergosterol as a marker of fungal biomass, on soil aggregate size class distribution and its carbon contents, and on the composition of soil organic matter.
7
Summary
(III) to investigate the temporal dynamics during grassland renewal from the chemical destruction of the existing vegetation and reseeding either by direct seeding or by prior tillage, and to investigate their effects on organic carbon and nitrogen in soil, on soil microbial carbon, on soil aggregate size class distribution, and on their carbon contents.
For the processing of (I), soil samples were taken during a long-term grazing experiment northwest of Göttingen (FOR BIOdiversity BENefit trial in Solling, Relliehausen), from three different extensively-grazed treatments in three soil depths (0-10 cm, 10-25 cm, and 25-40 cm) in April 2013. The different grazing pressures were determined by measuring the compressed pasture height during the vegetation period, using a rising-plate meter and subsequently adjusting the stocking rate.
The soil samples were analyzed for soil organic carbon (SOC) and nitrogen (Nt) contents, the coupling of carbon and nitrogen, soil microbial carbon (Cmic), basal respiration, and mineral nitrogen (Nmin). Furthermore, pH, clay content, oxalate soluble aluminum, and iron contents were determined. Before data analysis, weighted means were calculated for the stocks of SOC, Nt, Nmin, and Cmic concentrations and basal respiration rates with the proportion of each compressed pasture height class as a weighting factor. A two-factorial analysis of variance (ANOVA) with the factor grazing intensity and the factor block was used in case of normality of residuals and homoscedasticity; otherwise, a Welch ANOVA was used. The weighted stocks of SOC, Nt, Cmic, and basal respiration were not significantly affected (p ≤ 0.05) by grazing intensity.
The data were highly heterogeneous, which was probably caused by the heterogeneous soil mineralogy as well as by uncertainties in the analytical determination of the respective contents, the determination of bulk densities, and the stone contents. Thus, a large part of the variation of the organic carbon and total nitrogen contents can be explained regarding the content of oxalate soluble iron (multiple linear regression: R2 = 0.64). However, the contents of microbial carbon (R2 = 0.96) and the basal respiration rate (R2 = 0.9) are, in turn, explained to a significant extent by the organic carbon contents. Furthermore the possible effects of grazing intensity on the SOC and Nt stocks are presumably explained by the mineralogical variability. However, the low variability of the C/N ratios of different grazing intensities is attributed to a coupling of C and N and, in turn, suggests sufficient SOC and Nt supply in the extensive FORBIOBEN grazing trial.
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For the processing of (II), soil samples were taken in three soil depths up to 60 cm in depth in a grassland trial near Kiel managed by the Christian Albrechts University of Kiel. The grassland was established uniformly in 2004 after its preceding management as arable land. The trial was established in a randomized block design with three replicates and included these treatments: three cuts (3C) and five cuts (5C) per year; with and without N fertilization (N fertilization: 360 kg N ha-1 year-1 as calcium ammonium nitrate). The soil samples were analyzed for SOC and Nt stocks, Cmic and ergosterol as a marker for fungal biomass, soil aggregate size class distribution, their carbon contents, and the composition of soil organic matter (SOM). Three factorial ANOVAs with the factors cut (levels: 3 cuts and 5 cuts), fertilization (levels: N fertilization and no N fertilization), interaction between cut and fertilization, and factor block (three replicates organized in blocks) were conducted.
The SOC stocks from the 5C regime compared to the 3C regimes in soil depths of 0 ~ 10 cm were significantly higher. This was presumably caused by higher harvesting frequencies, which promote the growth of tiller and leaf, are high in photosynthesis, and can stimulate biomass production. Additionally, the SOC stocks were significantly higher in the treatment without N fertilization in a soil depth of 0 ~ 10 cm. N fertilization may result in a decrease of SOC stocks by increasing microbial activity and altering the C substrate utilization pattern through changes in plant biomass composition. Furthermore, higher biomass yields under the 3C compared to the 5C regime as well as different plant species compositions in the treatments may have also contributed to SOM dynamics. Plant species composition was mainly influenced by the differing cut and fertilization regime. The main plant species under the 5C regime without N fertilization at the time of soil sampling were Lolium perenne and Trifolium repens (a highly productive grass and a legume, respectively). A dense root growth in Lolium perenne in a soil depth of 0 ~ 10 cm and the positive effects of legumes on SOC sequestration presumably caused the increase of the SOC stock under the 5C regime without N fertilization. The Nt stocks were significantly higher under the 5C regime in a depth of 0 ~ 10 cm in comparison to the 3C regime, which is presumably related to the occurrence of Lolium perenne under the 5C regime.
Soil microbial C contents were significantly higher under the 5C regime than under the 3C regime, whereas N fertilization in significantly lower Cmic contents resulted in topsoil. This is presumably related to stimulated root exudation due to a higher harvesting frequency and complex changes in microbial competition and community structure due to the addition of N. Ergosterol contents in the surface soil were significantly higher under the 5C regime in comparison with the 3C regime, presumably caused by different root
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growth, exudation, and substrate quality. Cmic and the ergosterol contents were closely correlated to SOC stocks (Cmic: Spearman Rs = 0.81; ergosterol: Spearman Rs = 0.87) in topsoil. This indicates that, in the treatments that most likely resulted in higher root productions due to stimulation and plant species composition, microbial and fungal biomasses were stimulated.
For the aggregate distribution in the topsoil layer, a shift from small (250-1000 μm) to large (> 2000 μm) macroaggregates from the 3C to the 5C regime was detected, presumably caused by a higher concentration of roots and root exudates related to Lolium perenne, with its high amount of fine roots under the 5C treatment in a soil depth of 0-10 cm. Five cuts per year affects SOC and Nt stocks positively, as well as contents of large macro-aggregates, Cmic, and ergosterol, which indicate positive effects on the soil fertility of 5C in comparison with 3C.
The N fertilization resulted in slightly negative effects on SOC stocks and Cmic contents. However, as the plant species composition was strongly influenced by cut and fertilization, it is not possible to assign the results found to direct effects (e.g., stimulation of biomass production and root exudation) or to indirect effects due to a different plant species composition.
For the processing of (III) a grassland trial was established on a continuous cut grassland located in Oldenburg in 2013. The trial was managed and supervised by the Chamber of Agriculture of Lower Saxony and the Thünen Institute. In June 2013, a field trial was established and the treatments were arranged in a randomized complete block design with three replicates and consist of
• Treatment (i), chem: chemical sward killing with glyphosate, followed by direct seeding of grassland in 1-cm depth;
• Treatment (ii), phys: chemical sward killing with glyphosate followed by the use of a rotary cultivator, a moldboard plow (25-cm deep), and a land packer, afterwards seeding of grassland;
• Treatment (iii), continuous cut grassland as control.
Soil samples were taken five times during August 2013 to October 2014, each replicated four times in three soil depths. SOC stocks, aggregate size classes, and organic carbon stored in aggregate size classes were analyzed using two-way analysis of variance
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with the factors grassland renovation (control, chem, and phys) and block (blocks 1 to 3). For further data analysis, Spearman ́s rank correlation and regression analysis was conducted.
Soil carbon stocks showed no significant differences between the grassland renewal with or without plowing and control. This suggests that a grassland renovation, after neither a purely chemical destruction of sward nor a grassland renovation using a plow, had a direct impact on the loss of carbon stocks in the grassland soils. This is perhaps related to the rather low pH in the soil (on average, 4.8), resulting in hampered microbial biomass, which, in turn, hampered the degradation of organic material.
However, grassland renewal after plowing leads to an increase in microaggregate concentrations six days after plowing, compared to the grassland control in the surface soil and in the soil profile. This indicates that one-time plowing had a direct impact on soil aggregates and destroyed macroaggregates, which fragmented into microaggregates.
However, significant seasonal variations of macro- and microaggregate concentrations over time were visible. Higher macroaggregate concentrations were found during periods with increased rainfall following higher gravimetric water content in the soil, compared to periods with less rainfall and less gravimetric water content. Correlation analysis and multiple linear regression analysis have shown that the gravimetric soil water content had a putatively major influence on the distribution of aggregate size classes. Thus, lower gravimetric soil water content led to a higher concentration of microaggregates and a lower concentration of macroaggregates, while higher gravimetric soil water content led to lower microaggregate and higher macroaggregate concentrations.
The physical renovation two and seven months after plowing also led to a significantly higher microaggregate concentration in the surface soil compared to the grassland renewal without plowing, while the concentrations in the permanent grassland were in between. In the chemical renovation, the larger roots of the dead plants might still be largely undecomposed, protecting macroaggregates from degeneration. In the physical renovation, plowing affects macroaggregates negatively by dismantling them into microaggregates via mechanical forces. Furthermore, dead roots were rearranged and breached, which caused a loss of stability in the soil matrix. However, a year after plowing and grassland renovation, no significant difference existed compared to the other treatments. In the beginning, no effect of grassland renovation on SOC in aggregates was visible. However, later microaggregates become more important than macroaggregates in the sequestration of SOC compared to the unplowed control. Because of the late response in SOC in
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aggregates after the plowing event, it seems that the indirect effects (for instance, the degradation of the root systems of the dead plants) on soil aggregates had a wider influence than the direct physical impact of the plow. The plowing event in the physical renovation caused direct physical destruction of the aggregates and, indirectly, destruction of the root systems of the dead plants. However, impacts on soil macroaggregates were nullified one year after grassland renovation.
Chemical renovation resulted in higher macroaggregate concentrations compared with the physical renovation, especially two-to-seven months after the renovation, and in similar concentrations compared with the permanent grassland in any sampling time within one year. Presumably, dead plant roots could act as binding agents and stabilize aggregates for some time. The high temporal variation in the aggregate distribution within one year in the renovated as well as in the permanent grassland indicates that the soil moisture had a wide influence and that dry conditions in the soil led to a breakdown of larger aggregates.
From the findings obtained above, it can be concluded that the impact of the intensified use of grassland on carbon and nitrogen dynamics is highly dependent on location. First, in the implementation and the degree of intensification, major differences have been observed. Thus, a direct comparison are not directly achievable. However, it can be stated that intensified grassland management, except with a high application rate of mineral N fertilizer and a large removal of biomass (with a mean of 1459 g m-2), does not or only has a low tendency to have negative impacts on the SOC and Nt stocks and sequestration mechanisms. Unlike the loss of biodiversity through intensified use, the SOC stocks and sequestration mechanisms, which are inevitably linked to plant species diversity and the variety of soil organisms, tend to react more slowly to management changes, while showing relatively rapid regeneration. Thus, targeted and appropriate management seems to be important when favoring SOC stocks and sequestration mechanisms.Amount, composition and turnover of organic matter in topsoils and subsoils under mature beech forest
https://kobra.uni-kassel.de:443/handle/123456789/2017121554008
Two-third of the terrestrial carbon (C) is stored in soils, and up to 63 % of the soil organic C (SOC) is stored in subsoils (i.e. below 30 cm soil depth). Forest soils account for nearly 70 % of the global SOC, demonstrating their great importance regarding the global carbon cycle. The higher average age of the OC stored in subsoil indicates that the subsoil OC is more stable against microbial decomposition. The capability of soil to stabilize OC is affected by substrate characteristics (e.g. size, distribution, chemical composition) of the organic material (OM) as well as soil mineral characteristics (e.g. content of clay, iron and aluminum oxides, polyvalent cations). Both factors and thus the mechanisms of C mineralization and stabilization are assumed to differ widely between topsoil and subsoil. In contrast to forest topsoil, there is less information about the mineralization and stabilization of OC in forest subsoils. Soil enzymes are of particular importance for the decomposition of OM, but laboratory-based determination of their activities is elaborate and time-consuming. Application of visible and near infrared spectroscopy (vis-NIRS) may thus be beneficial for an estimation of their activities, but the usefulness of vis-NIRS remains controversial. The first study was a long-term incubation experiment to analyze the effects of concentration, spatial distribution and size of fine beech roots on their rates of decomposition in forest topsoil and subsoil. After the incubation experiment, subsamples were taken and several soil properties were determined. The rate of root application affected the mineralization at both soil depths, whereas the distribution had an effect in all topsoil treatments but only in the subsoil with the larger roots. Correlation analyses suggest an effect of the calcium and potassium supply on the microbial biomass and turnover of roots if the roots are locally concentrated. The data of this study indicate that in addition to root characteristics, the availability of macronutrients also has to be considered to elucidate their decomposition kinetics throughout the soil profile. In the second study, the influence of soil mineral characteristics on different OM stabilization mechanisms in relation to soil depth was analyzed. Horizontal samples of five pedogenetically different soils under mature beech were separated into four aggregate size and three density fractions which were quantified and characterized by FTIR spectroscopy. Additionally, the content of microbial biomass C and the cumulative basal respiration over the course of 14 days were determined. The relative proportion of stabilized OC increased with soil depth, independent of the soil type. Additionally, the percentage of bulk SOC that had been respired as CO2 within 14 days tended to increase with increasing soil depth, indicating a stronger separation of the bulk soil OM into a labile and a stable pool in the subsoil compared with the topsoil. The FTIR analyses suggest an enrichment in C=O groups of the OM with increasing soil depth, which might result from a higher degree of microbial processing. This study underlined the importance of forest subsoil for long-term C stabilization and simultaneously highlights the importance of subsoil OM for maintaining microbial activity as well as the subsoil nutrient cycle. In the third study, the estimation accuracies and the usefulness of vis-NIRS for the estimation of general soil properties and nine enzyme activities for two pedogenetically different sites were determined. For each site, a calibration sample consisting of two transects and an independent validation sample consisting of one transect were obtained and their absorbance spectra recorded. Standard partial least squares (PLS) regression and PLS regression with a genetic algorithm (GA-PLS) for variable selection, which may improve estimation accuracies, were used to evaluate the estimation accuracies. The study confirmed the usefulness of vis-NIRS for an estimation of SOC and N contents in independent transects, whereas the estimation accuracy of pH and texture was variable and dependent on the range of measured data. However, GA-PLS markedly improved estimation accuracies in cross-validation of the main soil properties compared to PLS, but generally not in the validation transects. Only a few enzyme activities could be estimated in independent validation, but there was no benefit of vis-NIRS for the estimation of their activities compared to estimations using laboratory data.
2017-12-15T00:00:00ZVormstein, SvendjaTwo-third of the terrestrial carbon (C) is stored in soils, and up to 63 % of the soil organic C (SOC) is stored in subsoils (i.e. below 30 cm soil depth). Forest soils account for nearly 70 % of the global SOC, demonstrating their great importance regarding the global carbon cycle. The higher average age of the OC stored in subsoil indicates that the subsoil OC is more stable against microbial decomposition. The capability of soil to stabilize OC is affected by substrate characteristics (e.g. size, distribution, chemical composition) of the organic material (OM) as well as soil mineral characteristics (e.g. content of clay, iron and aluminum oxides, polyvalent cations). Both factors and thus the mechanisms of C mineralization and stabilization are assumed to differ widely between topsoil and subsoil. In contrast to forest topsoil, there is less information about the mineralization and stabilization of OC in forest subsoils. Soil enzymes are of particular importance for the decomposition of OM, but laboratory-based determination of their activities is elaborate and time-consuming. Application of visible and near infrared spectroscopy (vis-NIRS) may thus be beneficial for an estimation of their activities, but the usefulness of vis-NIRS remains controversial. The first study was a long-term incubation experiment to analyze the effects of concentration, spatial distribution and size of fine beech roots on their rates of decomposition in forest topsoil and subsoil. After the incubation experiment, subsamples were taken and several soil properties were determined. The rate of root application affected the mineralization at both soil depths, whereas the distribution had an effect in all topsoil treatments but only in the subsoil with the larger roots. Correlation analyses suggest an effect of the calcium and potassium supply on the microbial biomass and turnover of roots if the roots are locally concentrated. The data of this study indicate that in addition to root characteristics, the availability of macronutrients also has to be considered to elucidate their decomposition kinetics throughout the soil profile. In the second study, the influence of soil mineral characteristics on different OM stabilization mechanisms in relation to soil depth was analyzed. Horizontal samples of five pedogenetically different soils under mature beech were separated into four aggregate size and three density fractions which were quantified and characterized by FTIR spectroscopy. Additionally, the content of microbial biomass C and the cumulative basal respiration over the course of 14 days were determined. The relative proportion of stabilized OC increased with soil depth, independent of the soil type. Additionally, the percentage of bulk SOC that had been respired as CO2 within 14 days tended to increase with increasing soil depth, indicating a stronger separation of the bulk soil OM into a labile and a stable pool in the subsoil compared with the topsoil. The FTIR analyses suggest an enrichment in C=O groups of the OM with increasing soil depth, which might result from a higher degree of microbial processing. This study underlined the importance of forest subsoil for long-term C stabilization and simultaneously highlights the importance of subsoil OM for maintaining microbial activity as well as the subsoil nutrient cycle. In the third study, the estimation accuracies and the usefulness of vis-NIRS for the estimation of general soil properties and nine enzyme activities for two pedogenetically different sites were determined. For each site, a calibration sample consisting of two transects and an independent validation sample consisting of one transect were obtained and their absorbance spectra recorded. Standard partial least squares (PLS) regression and PLS regression with a genetic algorithm (GA-PLS) for variable selection, which may improve estimation accuracies, were used to evaluate the estimation accuracies. The study confirmed the usefulness of vis-NIRS for an estimation of SOC and N contents in independent transects, whereas the estimation accuracy of pH and texture was variable and dependent on the range of measured data. However, GA-PLS markedly improved estimation accuracies in cross-validation of the main soil properties compared to PLS, but generally not in the validation transects. Only a few enzyme activities could be estimated in independent validation, but there was no benefit of vis-NIRS for the estimation of their activities compared to estimations using laboratory data.Effects of the application of biochar and organic fertilizers as well as temperature on soil carbon and aggregate dynamics
https://kobra.uni-kassel.de:443/handle/123456789/2017112753878
Soil aggregate formation is an important process for long-term carbon storage in soils. While it has been shown that plant residues exert a positive influence on aggregate formation, the effects of organic fertilizers such as cattle slurry or manure as well as the effects of biochar application to soil are less clear. Furthermore, little is known about the role of increased soil temperatures in aggregate dynamics.
The main objectives of this thesis were to analyse the effects of (i) cattle slurry and manure, (ii) the application of biochar and (iii) different temperature regimes on soil aggregate and carbon dynamics. For this, two incubation experiments and one field trial were analysed. In the laboratory experiments soil without macro-aggregates was incubated at different temperatures with biochar, slurry, manure or different mixtures of biochar and slurry. In the sampled field trial the factors increased soil temperatures and biochar application were analysed.
The results show no or negative effects of biochar application on soil aggregate formation, while slurry was found to have positive effects. The combined application of biochar and slurry led to lower aggregate yields than the solitary application of slurry. However, interactions between biochar and mineral soil particles were already found shortly after the application in both the incubations and in the field trial, leading to an increase of aggregate-occluded and thus protected soil organic carbon, especially in combination with a slurry application. Increased temperatures in steps of 10 °C led to an increased aggregate formation in the incubation experiments, presumably due to a metabolization of aggregate binding agents. In the field, however, a temperature increase of 2.5 °C did not show any effects on soil aggregate or carbon dynamics.
2017-11-27T00:00:00ZGrunwald, DennisSoil aggregate formation is an important process for long-term carbon storage in soils. While it has been shown that plant residues exert a positive influence on aggregate formation, the effects of organic fertilizers such as cattle slurry or manure as well as the effects of biochar application to soil are less clear. Furthermore, little is known about the role of increased soil temperatures in aggregate dynamics.
The main objectives of this thesis were to analyse the effects of (i) cattle slurry and manure, (ii) the application of biochar and (iii) different temperature regimes on soil aggregate and carbon dynamics. For this, two incubation experiments and one field trial were analysed. In the laboratory experiments soil without macro-aggregates was incubated at different temperatures with biochar, slurry, manure or different mixtures of biochar and slurry. In the sampled field trial the factors increased soil temperatures and biochar application were analysed.
The results show no or negative effects of biochar application on soil aggregate formation, while slurry was found to have positive effects. The combined application of biochar and slurry led to lower aggregate yields than the solitary application of slurry. However, interactions between biochar and mineral soil particles were already found shortly after the application in both the incubations and in the field trial, leading to an increase of aggregate-occluded and thus protected soil organic carbon, especially in combination with a slurry application. Increased temperatures in steps of 10 °C led to an increased aggregate formation in the incubation experiments, presumably due to a metabolization of aggregate binding agents. In the field, however, a temperature increase of 2.5 °C did not show any effects on soil aggregate or carbon dynamics.