Biochar As a Soil Amendment: Effects on Hydraulic and Physical Properties of an Arable Loamy Sand Soil.

Biochar is composed of any carbonaceous matter pyrolyzed under low oxygen exposure.  Its use as a soil amendment to address soil infertility has been accelerated by studies reporting positive effects of enhanced nutrient retention, cation exchange capacity, microbial activity, and crop growth over time.  It has also been considered as a method to sequester carbon for long periods of time as a result of its environmental persistence.  While the aforementioned effects are positive benefits of biochar’s use, its impact on soil physical properties and water flow are equally important in maintaining soil fertility.  This study aims to show how soil physical and hydraulic properties change over time with biochar addition.  To address these aims, we conducted a 12 week microcosm incubation experiment with arable loamy sand soils amended with biochar.  Biochar was created from almond shells and differs by pyrolysis temperatures (350°C, 700°C) and size (<250 μm, 1-2mm).  Additionally, biochar was applied to soil at a low (10 t/ha) or high (60 t/ha) rates.  Changes in soil water flow properties were analyzed by infiltration or pressure cell experiments immediately after mixing that were repeated after the incubation period to observe if and how flow is altered over time.  Data obtained from these experiments was inversely modeled in HYDRUS 1D to observe changes in hydraulic properties. Changes in soil physical properties were analyzed by aggregate stability via wet sieving after the incubation period.  We found significant increases in water flow with high temperature char with increasing application rate (7.2% and 12.9% increase for 10 t/ha and 60 t/ha, respectively) upon initial mixing.  Understanding the impact biochar addition on soil physical and hydraulic properties will provide insight into the feasibility of utilizing it as a method to increase water retention and soil health in general.