Lessons from a next generation carbon ranching experiment

•Reliable results require good replication and detection of pre-existing variation.•Severe summer (or fall) grazing increased SOC accrual in US Northern Great Plains.•SOC accrual was negatively (not positively) associated with root biomass.•SOC accrual was positively associated with soil N and density.•Management heterogeneity is likely necessary to sustainably maximize SOC accrual.