Evaluation of the surface affinity of water in three biochars using fast field cycling NMR relaxometry

Abstract

Many soil functions depend on the interaction of water with soil. The affinity of water for soils can be altered by applying soil amendments like stone meal, manure, or biochar (a carbonaceous material obtained by pyrolysis of biomasses). In fact, the addition of hydrophobic biochar to soil may increase soil repellency, reduce water-adsorbing capacity, inhibit microbial activity, alter soil filter, buffer, storage, and transformation functions. For this reason, it is of paramount importance to monitor water affinity for biochar surface (also referred to as 'wettability') in order to better address its applications in soil systems. In this study, we propose the use of fast field cycling NMR relaxometry technique with the application of a new mathematical model for data interpretation, as a valid alternative to the traditional contact angle (CA) measurements for biochar wettability evaluation. Either NMR or CA results revealed the same wettability trend for the biochars studied here. The advantage of NMR relaxometry over CA measurements lies in the possibility to obtain at the microscopic level a variety of different information in only one shot. In fact, while CA provides only wettability evaluation, NMR relaxometry also allows achievement of the mechanisms for water molecular dynamics on biochar surface, thereby leading to the possibility to understand better, in future research, the role of biochar in increasing soil quality and plant nutrition.

Multiscale nuclear magnetic relaxation dispersion of complex liquids in bulk and confinement

“…In fact, while CA provides only macroscopic wettability, NMR relaxometry allows a description of the mechanisms for water molecular dynamics on biochar surfaces, thereby leading to the possibility of understanding the role of biochar in increasing soil quality and plant nutrition. In fact a bimodal distribution of water molecules experiencing different environments was identified in each biochar/water mixture [34]. The narrow distribution of water molecules centered about T 1 $ 2.5 s is due to the oxygen dissolved in bulk water.…”

“…their wettability) when addressing their applications in soil systems. Bubici et al found that either NMR or contact angle (CA) results revealed the same wettability trend for the biochars they studied [34]. However, the advantage of NMR relaxometry over CA measurements lies in the possibility of obtaining a variety of different information at the microscopic level in a single experiment.…”

“…Fig. 14a shows the NMRD profiles of the logarithmic average hR 1 (s À1 )i of the fastest relaxing water distributions in contact with biochar surfaces obtained from conifer (A), poplar (B) and grapevine marc (C) [34]. As earlier reported in Pasquale et al [106], the R 1 values vary in the order: R 1(conifer biochar) < R 1(poplar biochar) < R 1(grapevine marc biochar) over the whole range of magnetic fields studied.…”

“…The T 2 -z-store-T 2 spin correlation sequence has been also applied to evidence water exchange in porous sandstone rocks [31], smectite gels with clay [32] and water and oil in rocks [33]. NMRD relaxometry techniques have also been proposed as a valid alternative to the traditional contact angle (CA) measurements for biochar water-wettability evaluation [34].…”

Behavior the Water in Typical Yellow Oxisoil of Central Amazon Under Biochar Application

“…However, it is possible that this characteristic is attenuated with the breakdown of hydrophobic compounds with the "aging" of the biochar (TEIXEIRA et al, 2017). Even with contradictory results, the addition of biochar in the soil still denotes promising responses, such as better soil structuring and decreased soil density (BUBICI et al, 2016;TEIXEIRA et al, 2017). In addition to increased crop productivity and soil fertility (CARVALHO et al, 2014).…”