Biochar represents a stable form of carbon-rich organic material produced by the pyrolysis of various biomass residues. It has the potential to stabilize organic carbon in the soil and improve soil fertility, water retention, and enhance plant growth. Despite its potential, there is limited information on the mutual relation of biochar texture with its physicochemical characteristics, morphology, and the content of organic matter. For these reasons, we studied three biochar samples with potential use in agriculture as soil supplements (NovoCarbo, Sonnenerde, Biouhel.cz). Our experimental approach performed on the individual sieved fraction of studied biochars (<0.5; 0.5–2.0; 2.0–4.0 and >4.0 mm) confirmed the importance of a selection of optimal source biomass material as the content of lignin, cellulose, and hemicellulose, together with the conditions of pyrolysis (temperature of pyrolysis), play a crucial role in the managing of the properties of produced biochar. Agronomically more stable biochars containing a higher content of organic matter and organic carbon, with alkaline pH response and well-developed aromatic porous structure, could be produced from lignin-based biomass residues at higher pyrolysis temperatures, which is an important finding taking into account the possible utilization of biochar in soils as a soil conditioner.

A sequential chemical extraction with a defined series of eluotropic organic solvents with an increasing polarity (trichloromethane < ethyl acetate < acetone < acetonitrile < n-propanol < methanol) was performed on peat-bog humic acid. Six organic fractions were obtained and subjected to a physicochemical characterization utilizing methods of structural and compositional analysis. Advanced spectroscopic techniques such as Attenuated Total Reflectance (ATR-FTIR), total luminescence, and liquid-state 13C NMR spectrometry were combined with elemental analysis of the organic fractions. In total, the procedure extracted about 57% (wt.) of the initial material; the individual fractions amounted from 1.1% to 19.7%. As expected, the apolar solvents preferentially released lipid-like components, while polar solvents provided organic fractions rich in oxygen-containing polar groups with structural parameters closer to the original humic material. The fraction extracted with acetonitrile shows distinct structural features with its lower aromaticity and high content of protein-like structural motifs. The last two—alcohol extracted—fractions show the higher content of carbohydrate residues and their specific (V-type) fluorescence suggests the presence of plant pigment residues. The extraction procedure is suggested for further studies as a simple but effective way to decrease the structural complexity of a humic material enabling its detail and more conclusive compositional characterization.

The classic way of land cultivation means the use of inorganic fertilizers that are salts that dissolve rapidly in a short time and improve soil fertility. This process negatively affects soil salinity and the life of microorganisms. The use of biochar as a soil conditioner is a promising solution. The aim of the work is to enrich the properties of less fertile soils and to enhance the growth of the model plant Zea mays (corn) by biochar application. We used four different soil types commonly spread in the Czech Republic – regosol, chernozem, cambisol and fluvisol representing a broad range of organic matter content. Also, we applied two different EBC (The European Biochar Certificate) certified biochars for use in agriculture. Corn seeds were germinated and cultivated for 3 months in repeated plant life cycles. Soils and biochar samples were characterized before and after cultivation by TGA, EA, BET, SEM, extraction of organic matter. The effect of biochar application was observed continuously through the measurement of plant height, the number of leaves and cobs. After the finalization of cultivation experiments, the dry mass of individual plants was measured, and root image analysis of every plant was performed. Fluvisol and cambisol have much higher organic matter content than regosol and chernozem. The application of biochar had the most significant impact on regosol regardless of the application dose; these results are in good agreement with the root image analysis. Furthermore, plants in soils treated with biochar had more corn cobs. The analysis on biochar samples showed the continual leaching of both organic and inorganic molecules from biochar to surrounding soil, which is crucial for its possible use as a soil conditioner and confirms the long-timescale positive effect on soil properties.

In the current work, humic acids (HAs) isolated from natural compost and unamended and amended soils in a medium-time field experiment were characterized to evaluate the effects of the amendment at rates of 124, 239 and 478 t/ha on their chemical, compositional and structural features. The impact of the application of compost on their properties was observed over 3 years. Humic acids were characterized using spectral methods and elemental analysis. Humic acid isolated from compost was predominantly aliphatic, with a larger content of nitrogen and low degree of aromaticity and humification. The typical maximum (280/345 nm) of HA obtained from compost lies within the T (tryptophan-like) region, which can be ascribed to proteinaceous organic materials. On the other hand, the HAs obtained from amended soil were mainly aromatic in character, with a larger distribution of oxygen-containing functional groups, molecular weight and greater aromaticity. Fluorophores of HAs obtained from amended soil lie within the C (humic-like) region with typical maxima centred in the range 430–450/500–540 nm, occurring usually in HAs isolated from soil, peat and lignite. According to ultra-violet/visible and Fourier-transform infrared (FTIR) spectroscopy, the larger oxygen contents of these HAs are associated with the substitution of aromatic rings by oxygen-containing functional groups such as carboxylic, hydroxyls and ethers. On the basis of FTIR spectra, it was shown that HAs obtained from amended soil 2 and 3 years after compost application were enriched by peptid, aromatic and polysaccharide compounds absorbing at 1540, 1515 and 1040/cm, respectively.

Biochar is a versatile carbon-rich organic material originating from pyrolyzed biomass residues that possess the potential to stabilize organic carbon in the soil, improve soil fertility and water retention, and enhance plant growth. For the utilization of biochar as a soil conditioner, the mutual interconnection of the physicochemical properties of biochar with the production conditions used during the pyrolysis (temperature, heating rate, residence time) and the role of the origin of used biomass seem to be crucial. The aim of the research was focused on a comparison of the properties of biochar samples (originated from oat brans, mixed woodcut, corn residues and commercial compost) produced at different temperatures (400–700 °C) and different residence times (10 and 60 min). The results indicated similar structural features of produced biochar samples; nevertheless, the original biomass showed differences in physicochemical properties. The morphological and structural analysis showed well-developed aromatic porous structures for biochar samples originated from oat brans, mixed woodcut and corn residues. The higher pyrolysis temperature resulted in lower yields; however, it provided products with higher content of organic carbon and a more developed surface area. The lignocellulose biomass with higher contents of lignin is an attractive feedstock material for the production of biochar with potential agricultural applications.

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