Fast field cycling NMR relaxometry characterization of biochars obtained from an industrial thermochemical process

Purpose

Biochar has unique properties which make it a powerful tool to increase soil fertility and to contribute to the decrease of the amount of atmospheric carbon dioxide through the mechanisms of C sequestration in soils. Chemical and physical biochar characteristics depend upon the technique used for its production and the biomass nature. For this reason, biochar characterization is very important in order to address its use either for agricultural or environmental purposes.

Materials and methods

Three different biochars obtained from an industrial gasification process were selected in order to establish their chemical and physical peculiarities for a possible use in agronomical practices. They were obtained by charring residues from the wine-making industry (marc) and from poplar and conifer forests. Routine analyses such as pH measurements, elemental composition, and ash and metal contents were performed together with the evaluation of the cross-polarization magic angle spinning (CPMAS) ¹³C NMR spectra of all the biochar samples. Finally, relaxometry properties of water-saturated biochars were retrieved in order to obtain information on pore size distribution.

Results and discussion

All the biochars revealed basic pH values due to their large content of alkaline metals. The quality of CPMAS ¹³C NMR spectra, which showed the typical signal pattern for charred systems, was not affected by the presence of paramagnetic centers. Although paramagnetism was negligible for the acquisition of solid state spectra, it was effective in some of the relaxometry experiments. For this reason, no useful information could be retrieved about water dynamics in marc char. Conversely, both relaxograms and nuclear magnetic resonance dispersion profiles of poplar and conifer chars indicated that poplar char is richer in small-sized pores, while larger pores appear to be characteristic for the conifer char.

Conclusions

This study showed the potential of relaxometry in revealing chemical?Cphysical information on industrially produced biochar. This knowledge is of paramount importance to properly direct biochar agronomical uses.     

Effects of afforestation with four unmixed plant species on the soil–water interactions in a semiarid Mediterranean region (Sicily, Italy)

Purpose

An assessment of the effect of plant cover on the properties of four afforested soils in central Sicily was performed with the aim of discriminating among them after 60?years of afforestation.

Materials and methods

Chemical and biochemical soil analyses were coupled to fast field cycling (FFC) NMR relaxation investigations in order to monitor surface interactions of water in water-saturated soils.

Results and discussion

The traditional soil analyses revealed that the most stable soil properties such as soil texture and pH are not affected by 60?years of afforestation. Soils developed under eucalyptus trees showed larger amounts of hydrophilic organic matter as compared to the soils under pines and cypresses. FFC-NMR relaxometry data revealed that water, partitioned in clay-, loam-, and sand-type pores, showed longitudinal relaxation time values affected by the interactions with the soluble carbon content.

Conclusions

The results of the present study evidenced the potential of FFC-NMR relaxometry in differentiating the effect of diverse plant cover on chemical and hydrological properties of soils developed on the same parent material. In fact, in contrast with the traditional physicochemical and biochemical soil characterizations, which were unable to reveal differences among soils afforested with different plant species, FFC-NMR was capable of monitoring differences in water dynamics as affected by the presence of the most soluble soil organic material.     

Introduction of exotic fish species and decline of native species in the lower Po basin,north‐eastern Italy

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