Biochar soil amendment for waste-stream diversion, nutrient holding capacity, and carbon sequestration in two contrasting soils

Biochar is organic matter that has been pyrolized under low oxygen conditions for use as a soil amendment. Currently biochar is viewed as a way to improve soil quality (e.g., increased nutrient and water holding capacity) and increase in soil carbon (C) sequestration. The use of biochar in soil is not new, yet little is known about the underlying mechanisms that control the interactions between biochar and soil following amendment. In the past, the effects of biochar addition on crop yields, soil properties and greenhouse gas (GHG) fluxes in both in-situ and controlled experiments have produced inconsistent results. These discrepancies may be uncovered in part by chemical and physical characterization of the biochar prior to amendment and identification of soil- and biochar-specific interactions. Furthermore, a more holistic consideration of the system may demonstrate the virtues of biochar amendment beyond the typical considerations of yield and gas flux. We expect that as the differences between the physical and chemical properties of the biochar and the soil increase, the impact on the soil quality metrics will also increase. For this study, we used a waste product (i.e., anaerobic digester sludge) biochar with 81.5% C, pH of 10.44, pH-independent charge for anion exchange capacity (AEC) and a pH-dependent charge for cation exchange capacity (CEC), 4.14% moisture content and 25.75 cmol¬c /kg exchangeable base cations. This biochar was incorporated into both a low and a high fertility Hawaiian field soil to quantitate biochar effects on crop yield, soil pH, CEC, AEC, hot and cold water extractable C and nitrogen, bulk density, phosphorus, soil microbial ecology, and GHG flux in varying soil conditions. Compared to the higher fertility soil, we hypothesized that the low fertility soil would demonstrate a greater increase in soil quality, including higher pH, CEC and water holding capacity. Two crop management practices were included with each soil: traditional tillage and ratoon (no-till) harvest. We expect that the physical soil differences due to tillage versus no-tillage with vegetative regrowth on the biochar-amended soil will increase the diversity of soil microbial community structure, potential for C sequestration, and overall valuation of biochar as a soil amendment for factors such as waste-stream diversion, nutrient holding capacity, and C sequestration in addition to crop yield and GHG flux. These different treatments paired with intensive biochar characterization will aid in identifying how specific biochar properties translate to soil quality changes and increase the ability to target specific soil deficiencies with a tailored biochar for maximum holistic benefits.