Can Walnut Shell-Based Biochar Provide Potassium to Support Plant Productivity?.

Biochar (a high carbon byproduct of pyrolysis) has received considerable research attention over the last decade as a potentially important soil amendment, contributing to soil quality and long-term soil C storage. Research has demonstrated a variety of benefits to soil physical properties and nutrient dynamics across a broad range of biochars generated from diverse biomass feedstocks. A major barrier to utilizing biochar is demonstrating a linkage between consistent physiochemical properties and agronomic and/or soil quality benefits. In the Sacramento Valley, Premier Mushroom is producing a unique and physiochemically consistent biochar from walnut shells (high porosity, surface area, and ~ 7-9% by mass Potassium content) as a byproduct of bioenergy. Walnut shell biochar has received limited research attention as a soil amendment with none focusing on its role as a local source of potassium to support carrot production.

This research evaluates the agronomic benefits of a locally produced walnut biochar, as a soil amendment providing potassium for crop growth and promoting soil quality, in a plot study of carrot production. Carrots are grown for eight weeks in continuously row crop soil collected from the CSU Chico University farm under an experimental design with individual treatments of biochar (2.5 & 5 tonnes/ha) and mushroom compost (2.5 & 5 tonnes/ha) and different combinations of 2.5 and 5 tonnes/ha of each respectively along with a no-amendment control. It was concluded that there was a direct correlation between the increasing rate of applied biochar and compost to larger concentrations of potassium when the soil and carrot flesh were analyzed; therefore biochar may help improve soil potassium fertility.

A central goal of this research is to develop an integrated assessment model that quantifies greenhouse gas emissions reductions associated with local amendment utilization and ecosystem services associated with enhanced soil quality.