Detectability of degradable organic matter in agricultural soils by thermogravimetry

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 CO2‐C evolution during incubation and changes in TML at 300°C with R2 > 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.

Diversified crop rotations and organic amendments as strategies for increasing soil carbon storage and stabilisation in UK arable systems

“…Likewise, compost fertilisation also resulted in a slightly higher relative weight loss and ion intensity for CO 2 (m/z 44) in the same temperature intervals at both soil layers. The results of the present study are also in agreement with a recent study conducted by Tokarski et al (2019), who observed that farmyard manure results in thermal mass losses mainly around 450 °C. Previous studies using thermogravimetry (TG) and differential scanning calorimetry (DSC) analysis indicate that exothermic peaks up to 350 °C are related to decomposition of organic matter rich in labile aliphatic and carboxyl groups, whereas identified peaks up to approximately 500 °C represent dominance of stable aromatic component classes.…”

“…Whilst the mixture of grasses and legumes and the use of organic amendments often result in an increased SOC stock (Sainju et al, 2006;Jian et al, 2020), mixed results have been reported due to the use of grass or legume during the ley period phases as well as due to the application of different organic amendments source (Mazzoncini et al, 2011;Aguilera et al, 2013;O'Dea et al, 2013). This might be due to differences in biomass production, C:N ratios and lignin content of the crops in the rotation as well as persistence of the organic amendments source to degradability in soils (Tokarski et al, 2019;Zhou et al, 2019). In the organic rotation, along with the grass-clover ley periods, other legumes (e.g., peas and beans) and vegetables (e.g., cabbage, lettuces, onions, and carrots) were cultivated in an 8-year period (2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018), which might have provided the finest balance between biomass production and optimal C:N ratio inputs for SOC accumulation benefits.…”

Natural soils analysis for future land use

“…During heating, the samples were ushed with an air ow of at least 200 ml/min at 76% relative humidity and 20°C. Further details can be found in [27,32,33,34].…”

“…This resulted in TML130 values higher than those expected in natural soils with the respective clay contents. Since the added fresh residues are biodegradable, the associated deviations decrease in proportion to the measured respiratory activity or degradation rate [33,34,41]. Fresh, unconverted, biodegradable organic substances, regardless of their chemical composition, can be quanti ed based on deviations between the measured TML and the TML calculated from the clay content.…”

The Influence of a CGA-BP Neural-Network-Based Aeration Oxygen Supply Prediction Model on the Maturity of Aerobic Composting

“…With the rapid development of the composting industry, compost producers are focusing their attention on the effective utilization of energy in the production process and on improving the quality of compost by controlling the forced ventilation system [1]. Aerobic composting can rationalize the use of livestock manure and straw and alleviate environmental pollution [2][3][4][5]. The amount of aeration will affect the microbial activity in aerobic composting, thereby affecting the normal fermentation of aerobic compost and delaying the composting maturity process.…”