Abstract Sustainable agricultural land use requires an assessment of degradable soil organic matter (SOM) because of its key function for soil fertility and plant nutrition. Such an assessment for practical land use should consider transformation processes of SOM and its sources of different origin. In this study, we combined a 120‐day incubation experiment with thermal decay dynamics of agricultural soils altered by added organic amendments. The aim was to determine the abilities and limits of thermal analysis as a rapid approach revealing differences in the degradability of SOM. The carried out experiments based on two independent sampling sets. The first sample set consisted of soil samples taken from non‐fertilized plots of three German long‐term agricultural field experiments (LTAEs), then artificially mixed with straw, farmyard manure, sheep faeces, and charcoal equal to 60 Mg ha −1 under laboratory conditions. The second sample set based on soil samples of different treatments ( e.g ., crop type, fertilization, cultivation) in LTAEs at Bad Lauchstädt and Müncheberg, Germany. Before and after the incubation experiment, thermal mass losses (TML) at selected temperatures were determined by thermogravimetry indicating the degradability of organic amendments mixed in soils. The results confirmed different microbial degradability of organic amendments and SOM under laboratory conditions. Thermal decay dynamics revealed incubation‐induced changes in the artificial soil mixtures primarily at TML around 300°C in the case of applied straw and sheep faeces, whereas farmyard manure showed mainly changes in TML around 450°C. Charcoal did not show significant degradation during incubation, which was confirmed by TML. Detailed analyses of the artificial soil mixtures revealed close correlations between CO 2 ‐C evolution during incubation and changes in TML at 300°C with R 2 > 0.96. Results of the soils from LTAEs showed similar incubation‐induced changes in thermal decay dynamics for fresh plant residues and farmyard manure. We conclude that the practical assessment of SOM could be facilitated by thermal decay dynamics if modified sample preparation and evaluation algorithms are used beyond traditional peak analysis.
Abstract Analysis of soil properties and soil organic matter dynamics requires the use of reliable and rapid analytical techniques. Included in such applicable techniques is thermogravimetry (TG) which, typically, measures mass losses of soil heated during a temperature ramping. Previous work revealed relationships between mass losses of 10°C intervals (TG indicators) and total organic carbon (SOC), total nitrogen (TN) and clay content, and relationships between mass losses of larger temperature intervals (TG fractions) and interactions between SOC, TN and clay. However, widespread application of these relationships is hampered by the requirement to equilibrate soils at 76% relative humidity (RH) prior to and during TG measurements. In this study we tested whether the relationships between mass losses and soil properties can be observed at 43% RH by analyzing 37 mostly arable and grassland soils. It was found that at 43% RH the same TG indicators correlated significantly with soil properties as at 76% RH, but the correlations with TN and clay contents were observed at lower temperatures. New equations were developed for rapid analysis of soil properties using TG indicators and for determination of TG fractions at 43% RH. The results indicated that for routine application of these TG approaches in soil science, it is necessary to include an RH parameter that accounts for potential shifts in diagnostic temperatures when modelling the relationships between TG data and soil properties. Highlights Thermogravimetry data correlate with soil organic carbon, nitrogen and clay at 43% RH. Clay and nitrogen correlated at lower temperature compared to 76% RH. New equations applicable at laboratory conditions were developed. Wider use of TG requires including information on ambient moisture.
Abstract Background Sewage sludge (SS) has been considered a potent source of soil nutrients. However, its direct application to agricultural soils have been discouraged owing to its toxic nature. Therefore, conversion and modification of SS to decrease its toxicity has resulted in advanced methods. Co-pyrolysis of SS with other amendments is an ideal treatment resulting in an environmentally safe and nutrient rich final products with additional properties to sequester carbon. In the present study, a novel biochar was produced through the microwave pyrolysis of SS mixed with zeolite and sawdust. The pyrolysis product was thus characterized for elemental composition, polycyclic aromatic hydrocarbons, via Fourier Transform Infrared Spectroscopy (FTIR), and for its effects on soil microbial characteristics, soil health and plant biomass after soil application. Results Results revealed that, the SS modification resulted in stable product with higher nutrients which further depend on the type and ratio of feedstock used. Its application to soil significantly improved soil chemical and microbiological properties and altered lettuce biomass. Conclusions We concluded that sawdust feedstock promoted nutrient availability in the resulting biochar and induced higher activity of nutrient mineralizing enzymes, whereas zeolite slowed down the release of nutrients from soil and putatively immobilized enzymes. This joint effect of sewage sludge biochar, sawdust and zeolite benefited the plant acquisition of nutrients in comparison with the microbial nutrient uptake. We thus conclude that microwave pyrolyzed SS could be used as a soil enhancer. Graphical Abstract
'/%3e%3cpath fill='%23fff' d='m8.751-17.959 10.11 11.373L3.997-9.844l13.94-6.1-7.692 13.129z'/%3e%3c/svg%3e)
