Effect of biochar on the physical and structural properties of a desert sandy soil

Biochar application to soil can be considered as a means to improve soil quality, thereby optimizing irrigation management and reducing irrigation needs, especially in dryland regions. This paper is aimed at investigating the effect of biochar (BC) on a desert sandy soil (Al Foah, United Arab Emirates) in terms of bulk density, porosity, water retention, plant available water (AWmax), aggregate stability (AS) and specific surface area (BET-SSA). BC was produced from forest biomass (Italy). Soil water retention was measured by the High Energy Moisture Characteristic (HEMC) and by pressure plate measurements, by using BC fractions equal to 0 (soil only), 0.014, 0.091, 0.23, 0.33 and 1 (BC only). The results indicated that BC significantly (p = 0.05) increased soil porosity and the amount of storage pores. As a consequence, water retention was enhanced and AWmax from 19.3 mm/m for the sandy soil (fbc = 0), to 60.8, 102.3 and 107.6 at fbc = 0.091, 0.23, and 0.33, respectively, was raised. No significant effects of BC were detected on the soil water retention curve of the BC-amended soil at fbc = 0.014, compared to the original condition. The significant increase in the structural index (SI) at fbc, ≥0.091, indicated that BC improved soil aggregate stability. The BET-SSA was measured by nitrogen adsorption measurements and indicated that the connected porosity was significantly increased by the 0.091 BC fraction. Both AWmax and SI were found to be correlated with BET-SSA. This showed an outcome that has been so far little investigated, namely that the BET-SSA played a significant role in the mechanism affecting the soil response to BC addition. The results showed that application of BC can improve soil structure and water retention and therefore optimize irrigation management by reducing irrigation needs, in the Al-Foah area and/or in similar dryland regions.