Can surface-applied biochar improve soil health and plant performance in a perennial cool-season grass forage system?

Biochar boasts several benefits as a soil amendment. However, few studies have evaluated its effectiveness in forage systems with limited soil disturbance and few external inputs. Biochar's effects vary with application method, rate, and frequency. To study the impact of various rates of biochar in forage systems, we conducted a 2-year field experiment on a tall fescue [Schedonorus arundinaceus (Schreb.)] dominated field in southeastern United States. In April 2017, we surface-applied six rates of wood biochar (0, 4.5, 9, 13.5, 18, and 22.5 Mg ha(-1)) in a randomized complete block design with four replications. We collected soil samples from 0 to 15 cm depth biannually from June 2017 to December 2018, and harvested plants in May 2017 and 2018. We determined forage biomass and nutritive value as well as soil pH, soil organic carbon (SOC) and total nitrogen (N), microbial biomass carbon (C) and nitrogen (N), and available nutrients. Biochar's effects on soil properties at 0-15 cm increased with, but were not proportional to, application rates. After 2 years, biochar rates of at least 9 Mg ha(-1) had resulted in a 16% to 24% increase in SOC, a 15% to 30% increase in total N, and a 12% to 21% increase in extractable P compared with an unamended control. At all rates, biochar reduced soil mineral N relative to the control during the first year after application. Biochar increased plant potassium (K) uptake by 16% to 26% in the first year but did not affect biomass or nutritive value in either year. Our results demonstrate that surface application of biochar has the potential to improve soil health in perennial cool-season grass forage systems without adversely affecting yields.