Background: Recent studies highlighted that biochar efficiency to improve soil fertility is enhanced
after it is blended with fresh organic materials. It was suggested that organic coating of inner-porous biochar surfaces
acts as a kind of “glue” for plant-nutrients, thereby allowing their slow release towards plant-roots and/or
Objective: The aim of the present study is to improve the understanding of the nature of the interactions between
fresh organic matter and a poplar biochar.
Method: Two fluorinated organic models were used as target molecules in order to apply heteronuclear (i.e. 19
fast field cycling (FFC) NMR relaxometry.
Results: The results suggest that organic coating can be stabilized by charge transfer interactions (involving electron-
rich systems of fresh organic matter and electron-poor sites provided by biochar), water bridging (between
biochar surface and fluorinated compounds) and van der Waals interactions (occurring between the biochar aromatic
system and the carbon chain of the fluorinated compound).
Conclusions: The weak interactions outlined above may be responsible for an induced dipole on the biochar organic-
cover. The induced dipole, in turn, can be involved in the adsorption of plant nutrients (which adsorb only
marginally on the un-coated biochar), while maintaining their availability for plants.