Assessing the influence of biochar on soil structure and soil water retention: a 1H NMR relaxometry study coupled with high-energy moisture characteristic technique on a laboratory scale

Production of biochar and its storage in soils have been suggested as an efficient way to mitigate global climate changes through carbon sequestration in soils. In addition, application of biochar to soils concomitantly results in increase of soil structure, improvement of crop yield and enhancement of drought tolerance by plants. Application of biochars to soils also promotes reduction of irrigation needs in arid and semiarid regions which are affected by droughts and considerable climate variability. In order to understand the molecular mechanisms involved in the positive effects of biochars applied to soils, soil structural stability and soil water retention capacity were investigated by high-energy moisture characteristic technique (HEMC) after amendment of a Sicilian soil with different amounts of an industrially produced biochar. HEMC was applied under laboratory conditions on re-packed soil samples mixed with the different biochar amounts. Matrix potential values were varied in the range 0- 150 cm. The soil/biochar samples were also investigated by fast field cycling (FFC) NMR relaxometry for the understanding of water molecular dynamics. Both HEMC and FFC NMR relaxometry results revealed that water mobility increased with increasing biochar amounts in soils. These results confirmed that soil amendment with biochar may enhance water availability, and hence soil solution, for plant nutrition. Finally, to the best of our knowledge the present study combined for the first time results from HEMC and FFC NMR relaxometry, thereby showing the suitability of both techniques for the evaluation of soil structural stability.