Structure alteration of a sandy-clay soil by biochar amendments

The aim of the present study was to investigate structure alterations of a sandy-clay soil upon addition of different amounts of biochar (f (bc) ). All the f (bc) samples were analyzed by high energy moisture characteristic (HEMC) technique and H-1 nuclear magnetic resonance (NMR) relaxometry. HEMC was applied in order to evaluate aggregate stability of biochar-amended soil samples. H-1 NMR relaxometry experiments were conducted for the evaluation of the pore distributions through the investigation of water dynamics of the same samples. The HEMC technique revealed improvement in aggregate stability through measurements of the amount of drainable pores and the stability ratio. The latter increased as the amount of biochar was raised up. The H-1 NMR relaxometry revealed a unimodal T (1) distribution for both the sole sandy-clay soil and the biochar. Conversely, a bimodal T (1) distribution was acquired for all the different f (bc) samples. Improvement in aggregate stability was obtained as biochar was progressively added to the sandy-clay soil. A dual mechanism of water retention has been hypothesized. In particular, intra-aggregate porosity was indicated as the main responsible for molecular water diffusion when f (bc) comprised between 0 and 0.33. Conversely, inter-aggregate porosity resulted predominant, through swelling processes, when f (bc) overcame 0.33.