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Abstract: Technologies for agro-industrial feedstock utilization such as pyrolysis, gasification and hydrothermal carbonization at industrial scale develop rapidly. The thermochemically converted biomasses of these production technologies have fundamentally different properties controlled by the production technology. This is reflected by general properties such as pH or elemental composition. The 13C NMR spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy and black carbon results confirmed these observations showing that hydrochars have lower proportions of aromatic compounds than biochars (less stable) but are rich in functional groups (higher cation exchange capacity) than biochars. Analyses of pollutants indicate that polycyclic aromatic hydrocarbons as well as dioxin contents of most samples were under the threshold values recommended by International Biochar Initiative and European Biochar Certificate. In conclusion, biochars and hydrochars are entirely different from each other and these materials will probably have a complementary reaction in a soil environment. [Copyright &y& Elsevier]

Abstract: Hydrothermal carbonization (HTC) of biomass may be a suitable technique to increase its carbon sequestration potential when applied to soils. However, the properties of end products of HTC (hydrochars) could be significantly influenced by feedstock source and temperature during the carbonization process. This study focused on chemical modification of wheat straw, poplar wood and olive residues through HTC at different temperatures (180°C, 210°C and 230°C). Besides general properties such as pH, electrical conductivity (EC), ash content, elemental composition and yield, we evaluated bulk chemical composition (13C NMR) and contribution of specific compounds (lignin and black carbon). Moreover, the possible environmental risk of using hydrochars was assessed by determining their polycyclic aromatic hydrocarbon (PAH) and their dioxin contents. Our results showed that hydrochars were generally acidic with a pH value below 5. The highest EC (1710μS/cm) and ash content (10.9%) were found in wheat straw derived hydrochars. Hydrochar yields and C recovery decreased with increasing temperature to about 50% and 75%, respectively for all feedstocks at 230°C. N recovery increased with increasing temperature but N content of feedstock is more important. H/C and O/C ratios showed a linear decrease with increasing production temperature for all feedstocks. O–alkyl C decreased while alkyl C and aromatic C increased with increasing temperature and no significant feedstock dependence could be observed. Carboxyl C was not influenced by feedstock and temperature. Lignin content decreased with increasing temperature, while its oxidation degree and the content of black carbon and PAH contents increased. We conclude that transformation of biomass was most advanced at 230°C only. Feedstock did not significantly influence the chemical composition of the hydrochars apart from N content and recovery. Instead, HTC temperature is the main driver determining the chemical composition of hydrochars. Environmental risk of investigated hydrochars is low with respect to PAH and dioxin contents. Despite the advanced biomass transformation during the HTC process at 230°C, chemical properties indicated that the end product might have a less stable structure than pyrochar. Considering the higher hydrochar yields and C and N recoveries, its C and N sequestration potential in soil could have some advantages over hydrochars but this still remains to be evaluated. [Copyright &y& Elsevier]

• Ridge and furrows were studied by morphological and physicochemical analyses. • Study sites revealed a diversity in morphology, environmental setting and use. • Ridge and furrow cultivation was and is influencing the environment. • Elevated amounts of P and δ15N indicate the application of manure in the past. Ridge and furrow cultivation is an example for a historic agriculture technique that has been very common in Germany, especially during medieval times. It seemed to be well-known how the ridge and furrows (RIFUs) were used and formed but previous studies came to contradictory conclusions which raised additional questions concerning their formation. Furthermore, the RIFUs' morphological and physicochemical soil properties and their influence on current soils that developed after the RIFUs had been abandoned are not fully understood. In order to answer these questions, morphological and physicochemical analyses (pH, EC, TOC, TN, δ15N, C:N ratios, "Olsen P", soil texture) were conducted on 11 preserved RIFUs in forested areas of Northern and Central Germany. The results showed that the studied RIFUs occur on sites with different properties (e.g. soil texture, inclination, vegetation) and presented various morphological shapes. They are also characterised by differences in the formation of soil horizons and general low TN (<1.5 g kg−1) and TOC (<10 g kg−1) contents. However, higher contents at some sites comparing to their references, indicated that the RIFU cultivation promoted a slight long-lasting soil improvement if not induced by secondary soil processes after RIFU use. Moreover, for some sites, high P and δ15N values may suggest the application of manure. Recent morphological changes also had a significant influence on some study sites. In summary, neither the formation and agricultural strategies of RIFU cultivation nor their function and any influences on the current soil and woodland characteristics can be regarded as identical for all RIFU sites. [ABSTRACT FROM AUTHOR]

Abstract Chernozems and Chernozem-like soils are widespread e.g. in Central Germany but its formation is still controversially discussed. Clustered findings of Luvic Phaeozems and buried dark soil horizons in the Westphalian Hellweg Loess Belt (North Rhine-Westphalia) are traditionally interpreted as relics of early Holocene Chernozems. More recent research raised the question whether these soils are of (pre-) historic anthropogenic origin. Field observations in the east of Dortmund revealed the existence of buried black horizons in hillslope hollows. The underlying Stagnic Luvisol was penetrated by darkish clay illuviation veins forming a polygonal pattern. This feature was also found below the plough horizon in Luvisols beyond the hillslope hollows. A multi-analytical approach was used in order to clarify whether the black soil horizons are natural relics or man-made. In order to identify fire-derived black carbon (microcharcoal), benzenepolycarboxylic acids were used as molecular markers. Beside the position of the fossil black horizons on top of a well-developed Stagnic Luvisol, micromorphological thin section analysis confirmed the colluvial origin of the black horizons. Total organic carbon contents of the black horizons were only ∼1%, whereas high black carbon concentrations indicate large amounts of fire derived organic matter. High concentrations of black carbon were also found in the clay illuviation veins, testifying to a formerly more widespread occurrence of black carbon enriched soils. Radiocarbon ages of charcoal particles from the black horizons prove fire activities during the late Neolithic and Bronze Age (e.g. slash-and-burn). Finally, our results strongly indicate that the Chernozem-like soils in the study area are man-made and natural Chernozem formation can be excluded. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Various organic amendments are scrutinized as potential agricultural management strategies to ensure soil productivity while mitigating climate change due to the accumulation of soil organic matter (OM). The objectives of this experiment were to study the effects of biochar and biogas digestate versus mineral fertilizer on crop aboveground biomass as well as fractions and mineralization of soil organic carbon (SOC). Samples of a sandy Cambisol were taken 14 months after establishment of a field experiment in Germany. Treatments included application of equal nitrogen in the form of mineral fertilizer or liquid biogas digestate without biochar (B 0), with 1 Mg biochar ha−1season−1 for two growing seasons (B 2), or with 40 Mg biochar ha−1 application (B 40). Soil fractionation in water separated water-extractable and free particulate (fPOM) OM, followed by sonification and sieving to isolate occluded particulate (oPOM) and < 20 μm aggregate-occluded and mineral-associated OM. CO 2 emissions were measured during 92-day laboratory incubations at 10 and 20 °C. Analysis of variance found digestate lowered (p < 0.05) rye aboveground biomass compared to mineral fertilizer (9.3 vs. 10.6 Mg ha−1), while biochar had no effect. B 40 treatments increased C mineralization during incubation by 16% and contained 3.8 times more SOC than B 0 treatments. This additional SOC was allocated to fPOM (52%), oPOM (22%), and the <20 μm fraction (26%). Digestate application increased SOC content of oPOM by 11% compared to mineral fertilizer. Furthermore, combined application of 40 Mg biochar ha−1 with digestate resulted in 20% more SOC in the <20 μm fraction than biochar with mineral fertilizer. The lack of a significant fertilizer or biochar-fertilizer interaction effect on C mineralization during incubation demonstrates the stability of SOC from digestate alone or in combination with biochar. The absence of significant differences in SOC content between B 0 and B 2 treatments demonstrates the difficulty of documenting SOC sequestration in the field at low biochar application rates. Unlabelled Image • Compared to mineral fertilizer, digestate increased physically stabilized soil C. • 14 months after biochar application, 52% of additional soil C was not occluded. • Biochar increased CO 2 emissions during laboratory incubation, while digestate did not. • Biogas digestate resulted in lower aboveground crop biomass than mineral fertilizer. • 40 Mg biochar ha−1 applied to a sandy soil had no effect on aboveground crop biomass. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biochar amendments directly affected the soil carbon cycle. [•] Biochar reduced organic matter (OM) mobilization from a soil. [•] Carbon oxidation state of OM mobilized from a soil increased after biochar amendment. [•] Soil released more aromatic OM after turning anoxic. [ABSTRACT FROM AUTHOR]

Highlights: [•] Acid dichromate oxidation distinguishes reactivity of biochars and hydrochars . [•] Feedstocks may significantly influence biochar reactivity. [•] Holocene charcoal is not suited as standard material due to low reactivity. [Copyright &y& Elsevier]