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 (NO) emissions and leachate nitrate (NO) 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 in a 100-d laboratory incubation ( = 4 replications). Results indicate that biochar increased average daily NO emissions in IR by 30% but decreased them by 39% in BR. In both positions, biochar decreased NO 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 NO 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 NO emissions depending on spatially distinct soil management history. Findings from this laboratory study stress the need for field research evaluating spatial differences in biochar NO mitigation potential.