Hydration efficiency and wettability of two biochars

The ability to capture and retain water is an important feature for substrate components. Suitable wettability of these components can lead to a more uniform distribution of water and nutrients within the plant root zone. Biochars are considered porous materials with both external and internal pores which makes them a potential substrate component with water retention properties. For this study, biochars were produced from two feedstocks, pine wood chips (Pinus taeda L.) and rice hulls (Oryza sativa L.), through gasification at a production temperature of 745°C with a residency of three hours. Unadulterated samples of both feedstocks were compared to their respective biochar counterparts to distinguish the effects of charring on hydration efficiency and wettability, as well as determine the biochars water-holding capacities. The charring process did not adversely affect hydration efficiency in the pine wood chip biochar, as the pine wood chip feedstock had nearly identical wetting curves to its biochar. Rice hulls had a very low ability to capture and retain water. Both biochars had an increase in water-holding capacity compared to their respective feedstocks; however, this did not appear to have a positive effect on initial wettability as both biochars never reached their water-holding capacities within ten irrigation events. This could indicate issues with hydrophobicity in biochars. However, this tested the biochars alone without other substrate components. Combining biochar with other components may change the receptiveness of biochar's porous surface to hydration.