Potential nitrogen losses in relation to spatially distinct soil management history and biochar addition

Soil functional zone management strategies including ridge tillage have been shown to increase in-row (IR) compared with between-row (BR) soil nitrogen (N) availability due to the development of contrasting soil properties and carbon (C) and N cycling processes. However, potential N losses may also increase for IR positions, representing an environmental tradeoff. Although biochar has putative contributions to tightening N cycles, its effect within spatially distinct management zones has not been quantified. This study evaluated the potential for biochar to reduce soil nitrous oxide (N₂O) emissions and leachate nitrate (NO₃ ^-) concentrations as influenced by changes in soil properties after 5 yr of ridge tillage in a silty clay loam soil. Soil columns for IR and BR positions were treated with and without biochar at 10 Mg ha^-1 in a 100-d laboratory incubation (n = 4 replications). Results indicate that biochar increased average daily N₂O emissions in IR by 30% but decreased them by 39% in BR. In both positions, biochar decreased NO₃ ^- concentrations in soil solution and leachate by 11 to 20% and 10 to 15%, respectively. Our findings suggest that long-term changes in soil C and N cycling processes may increase the potential for N₂O emissions in IR compared with BR positions. Although most biochar studies have not accounted for within-field soil variability, our results indicate that biochar may differentially affect soil N₂O emissions depending on spatially distinct soil management history. Findings from this laboratory study stress the need for field research evaluating spatial differences in biochar N₂O mitigation potential.