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.
•Production technologies influences fundamentally chemical properties of chars.•Carbonized materials have different behaviour in soil environment.•Environmental risk of chars is low with respect to PAH and dioxin contents.•Certification standard for biochars is not suitable for hydrochars.•Commercial scale reactors are able to produce high quality biochars according to the regulations of the EBC or IBI.
Chernozems/Phaeozems are important agricultural resources and have been intensively used for millennia. However, their origin and age are still controversial. In Europe, the westernmost ...widespread Chernozem/Phaeozem area is located in Central Germany. In contrast to other German regions with anthropogenic Chernozems/Phaeozems, their natural origin is suggested in connection with intensive bioturbation. Yet, radiocarbon is unsuitable for decoding Chernozem/Phaeozem formation so this hypothesis remains untested, whereas single-grain luminescence dating allows to discriminate between different soil sub-processes and formation phases. We applied single-grain feldspar luminescence to a Central German Chernozem that was buried during the Bronze Age and subsequently protected from pedogenic processes. For the first time, we could directly determine timing and rate of Chernozem/Phaeozem formation in Central Europe by dating bioturbation as the dominant soil forming process. Accordingly, Chernozem/Phaeozem formation started at the latest in the Early Holocene prior to Neolithic settlement indicating a natural origin of Central German Chernozems/Phaeozems, and Chernozem/Phaeozem formation ceased around 6-5 ka when the regional climate became more humid. Our effective soil reworking rates show that earthworm bioturbation in Chernozems/Phaeozems is more intense than ant-dominated bioturbation, but significantly less intense than bioturbation by lugworms or ploughing. The latter effect allows to identify prehistoric ploughing in paleosols.
Biochar has been shown to improve soil quality and crop yields. Furthermore, thanks to its high carbon content (C) and stable chemical structure, biochar can sequester C in the soil for a long time, ...mitigating climate change. However, the variability in published biochar stability in the soil makes verifying this trait under different environmental and agricultural conditions necessary. Moreover, most of the published literature refers to short-term incubation experiments, which are considered to not adequately represent long-term dynamics under field conditions. This article reports the results of a field experiment carried out in a vineyard near Merano, northern Italy, where the stability of woodchips biochar in soil, its impact on the total soil C stocks as well as on the original soil organic C (priming effect) were studied over two years. Vineyard soil (Dystric Eutrochrept) was amended with biochar (25 and 50 t ha−1) alone or together with compost (45 t ha−1) and compared with unamended control soil. Two methods assessed the stability of biochar in soil: the isotopic mass balance approach and the quantification of Benzene PolyCarboxylic Acids (BPCAs), molecular markers of biochar. The amount of C in the soil organic matter (SOM-C) was determined in the amended plots by subtracting the amount of biochar-C from the total soil organic C stock, and the occurrence of priming effect was verified by comparing SOM-C values at the beginning and at the end of the experiment. Results did not show any significant biochar degradation for both application rates, but results were characterized by a high variation. The application of 50 t ha−1 of biochar significantly increased soil C stock while no effect of biochar on the degradation of SOM-C was observed. Results were confirmed in the case of biochar application together with compost. It can be concluded that the use of woodchips biochar as a soil amendment can increase soil C content in the medium term. However, further analyses are recommended to evaluate the impact of biochar on climate change mitigation in the long term.
Biochars are new, carbon-rich materials that could sequester carbon in soils improve soil properties and agronomic performance, inspired by investigations of Terra Preta in Amazonia. However, recent ...studies showed contrasting performance of biochar. In most studies, only pure biochar was used in tropical environments. Actually, there is little knowledge on the performance of biochar in combination with fertilizers under temperate climate. Therefore, we conducted an experiment under field conditions on a sandy Cambisol near Gorleben in Northern Germany. Ten different treatments were established in 72-m
2
plots and fivefold field replicates. Treatments included mineral fertilizer, biogas digestate, microbially inoculated biogas digestate and compost either alone or in combination with 1 to 40 Mg ha
−1
of biochar. Soil samples were taken after fertilizer application and maize harvest. Our results show that the biochar addition of 1 Mg ha
−1
to mineral fertilizer increased maize yield by 20 %, and biochar addition to biogas digestate increased maize yield by 30 % in comparison to the corresponding fertilizers without biochar. The addition of 10 Mg ha
−1
biochar to compost increased maize yield by 26 % compared to pure compost. The addition of 40 Mg ha
−1
biochar to biogas digestate increased maize yield by 42 % but reduced maize yield by 50 % when biogas digestate was fermented together with biochar. Biochar-fertilizer combinations increased K, Mg and Zn and reduced Na, Cu, Ni and Cd uptake into maize. Overall, our findings demonstrate that biochar-fertilizer combinations have a better performance than pure fertilizers, in terms of yield and plant nutrition. Therefore, an immediate substitution of mineral fertilizers is possible to close regional nutrient cycles.
•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.
► Hydrothermal carbonization temperature is the main control of hydrochar chemistry. ► Feedstock did not influence hydrochar composition except for N content and recovery. ► Environmental risk of ...hydrochar is low with respect to PAH and dioxin contents. ► Hydrochar may be less stable than pyrochar but show higher C and N yields.
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.
Biochar composting experiments were performed to determine whether composting is a suitable method to accelerate biochar surface oxidation for increasing its reactivity. To assess the results, ...surface properties of Terra Preta (Brazil) and ancient charcoal pit (Northern Italy) biochars were additionally investigated. Calculation of O/C ratios by energy-dispersive X-ray spectroscopy demonstrated the anticipated increasing values from fresh biochars (0.13) to composted biochars (0.40), and finally charcoal pit biochars (0.54) and ancient Terra Preta biochars (0.64). By means of Fourier transformation infrared microscopy, formation of carboxylic and phenolic groups on biochars surface could be detected. Carboxylic acids of three composted biochars increased up to 14%, whereas one composted biochar showed a 21% lower proportion of carboxylic acids compared to the corresponding fresh biochar. Phenolic groups increased by 23% for the last mentioned biochar, and on all other biochars phenolic groups decreased up to 22%. Results showed that biochar surface oxidation can be accelerated through composting but still far away from ancient biochars.
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.
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In recent years, biochar has been discussed as an opportunity for carbon sequestration in arable soils. Field experiments under realistic conditions investigating the CO2 emission from soil after ...biochar combined with fertilizer additions are scarce. Therefore, we investigated the CO2 emission and its 13C signature after addition of compost, biogas digestate (originating from C4 feedstock) and mineral fertilizer with and without biochar (0, 3, 10, 40 Mg biochar/ha) to a sandy Cambisol in Northern Germany. Biomass residues were pyrolized at ~650°C to obtain biochar with C3 signature. Gas samples were taken biweekly during the growing season using static chambers three years after biochar substrate addition. The CO2 concentration and its δ13C isotope signature were measured using a gas chromatograph coupled to an isotope ratio mass spectrometer. Results showed increased CO2 emission (30%–60%) when high biochar amount (40 Mg/ha) was applied three years ago together with mineral fertilizer and biogas digestate. On average, 59% of the emitted CO2 had a C3 signature (thus, deriving from biochar and/or soil organic matter), independent of the amount of biochar added. In addition, our results clearly demonstrated that only a small amount of released CO2 derived from biochar. The results of this field experiment suggest that biochar most likely stimulates microbial activity in soil leading to increased CO2 emissions derived from soil organic matter and fertilizers mineralization rather than from biochar. Nevertheless, compared to the amount of carbon added by biochar, additional CO2 emission is marginal corroborating the C sequestration potential of biochar.
Biochar made of biomass residues co‐applied to mineral fertilizer, biogas digestate and compost increases the CO2 emissions of an agriculturally used sandy soil in Northern Germany. The enhanced CO2 emissions only derived to a minor extend from added biochar. Our data from a field experiment under realistic conditions enhance the knowledge on C sequestration potential of biochar as soil amendment in agriculture and its contribution to soil organic matter dynamics.
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