The role of biochar porosity and surface functionality in augmenting hydrologic properties of a sandy soil

• Published in: The Science of the total environment Vol. 574; pp. 139 - 147
• Main Authors: Suliman, Waled, Harsh, James B., Abu-Lail, Nehal I., Fortuna, Ann-Marie, Dallmeyer, Ian, Garcia-Pérez, Manuel
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.01.2017
• Subjects: Hydrological properties of biochar; Oxidized biochar; Quincy sand; Soil water retention; Oxidized biochar; Quincy sand; Soil water retention; Hydrological properties of biochar
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2016.09.025

This paper reports studies to elucidate the potential relationships between porosity and surface functionality of biochar and soil water retention characteristics. The biochars studied were produced from pine wood (PW), hybrid poplar wood (HP), and pine bark (PB) at temperatures of 350°C and 600°C. The resulting materials were then oxidized under air at 250°C to generate oxygenated functional groups on the surface. All biochar were thoroughly characterized (surface and bulk properties) and their hydrological properties measured in blends with Quincy sand. We prepared 39 microcosms for this study to examine the effect of biochar functionalities and porosity on the hydro-physical properties of Quincy sand. Each biochar was thoroughly mixed with the soil at 20gkg−1. The field capacity, wilting point, and total available soil moisture of the bio-char/Quincy sand mixtures were measured for both dry and wet ranges. The soil water potentials and soil water contents were fitted using the model of van Genuchten. Our results indicated that the amount of oxygenated functional groups on the surface of biochars clearly differentiated the biochars in terms of hydrophilicity, with the oxidized biochars being superior, followed by the low-temperature biochars, while the high temperature biochars possessed lowest hydrophilicity. As a result, oxidized biochars exhibited better wettability compared to unoxidized biochars, regardless their feedstock source. Significant correlation occurred between the total acidic functional groups on biochar surface and water contents at different matric potentials. Over a wide range of soil water potentials, oxidized biochar-soil mixtures held more water than the unoxidized biochar-soil mixtures except in the region between −0.1 and −5kPa of ψ, which is near saturation. Soil water contents at different matric potentials were significantly inter-correlated (P<0.01) and correlated with bulk densities of biochar-amended soil samples. [Display omitted] •Oxidized biochars retain more water than unoxidized ones.•Air oxidation of biochar is a suitable way to enhance water holding capacity of biochar and its blends with soils.•There is a positive correlation between total acidic functional groups on the surface of biochar and soil water retention.•The capability of biochar to retain soil water is a function of the combination of its porosity and surface functionality.