Nitrogen utilization and environmental losses in organic greenhouse lettuce amended with two distinct biochars

The potential of biochar to prevent nitrogen (N) losses and improve plant performance were studied across various levels of N input for two growing seasons in mesocosms simulating an organic lettuce production system. A silt loam soil was amended with pine chip (PC) and walnut shell (WS) biochar (10tha^-1) in combination with five organic N fertilization rates (0, 56, 112, 168, and 225kgNha^-1). The N output through harvest, leachate, and N₂O emissions were measured to assess N utilization and environmental losses of biochar-amended soils. For both biochars, only at the 100% N fertilization rate was lettuce biomass production improved with significant increases in N use efficiency (NUE); however, only PC biochar decreased N losses via leaching (at 100% N fertilization rate) and seasonal N₂O emissions (at 50% N fertilization rate). Thus, due to increases in plant biomass and decreases in N losses, PC biochar significantly decreased the ratio of N lost over N exported in biomass. Findings from this study suggest that both WS and PC biochars can improve organic lettuce production but only at 225kgNha^-1. Decreases in N losses via leachate and N₂O emissions vary with fertilization level and biochar type.