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

Authors: BAECHLE, B - University Of Illinois; Davis, Adam; PITTELKOW, C - University Of Illinois

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2017
Publication Date: 12/7/2017
Citation: Baechle, B., Davis, A.S., Pittelkow, C.M. 2017. Potential nitrogen losses in relation to spatially distinct soil management history and biochar addition. Journal of Environmental Quality. 47(1):62-69.

Interpretive Summary: There is increasing farmer interest in managing agricultural soils for improved environmental stewardship, including more efficient use of nitrogen fertilizer and storage of carbon. Ridge tillage is an approach to soil management that has been demonstrated to provide both of these services by concentrating organic nutrients in the crop row and limiting soil disturbance between crop rows. However, greater nutrient availability in the crop row may also result in greater losses of nitrous oxide, a greenhouse gas, from the soil. The objectives of this study were to evaluate whether addition of biochar to a ridge tilled soil can mitigate nitrogen losses from inter-row (IR) and between-row (BR) positions. We incubated intact soil cores representing four treatments (IR and BR positions treated with and without biochar) under controlled environmental conditions for 100 days, subjecting the cores to weekly leaching events. Soil nitrous oxide emissions were measured every 3-4 days and nitrate concentrations in soil solution and leachate were determined weekly. Results indicated that row position strongly affected nitrous oxide emissions (daily emissions were 2.5-fold greater in IR than in BR), but did not affect average nitrate concentrations in soil solution or leachate. Biochar increased daily average nitrous oxide emissions in IR by 30%, but decreased them by 39% in BR. However, biochar consistently decreased nitrate concentrations in soil solution and leachate in both row positions by 8-14% and 11-15%, respectively. Findings from this short-term incubation indicate that biochar additions may help to improve the environmental performance of ridge till systems.

Technical Abstract: Soil functional zone management has been shown to increase in-row (IR) compared to between-row (BR) soil N availability, potentially enhancing crop N uptake and fertilizer use efficiency. It remains to be determined whether N losses are also higher for IR positions, which would diminish the water quality benefits of this strategy; soil amendments to proactively prevent N losses could protect these benefits. Biochar amendments are being evaluated for their putative contributions to tightening N cycles, but few investigations have quantified biochar performance within distinct soil functional management zones in a field where carbon and N cycling processes differ. The objectives of this study were to evaluate N losses from IR and BR positions in a laboratory incubation following five years of ridge tillage in a silty clay loam soil in Illinois, USA and to determine whether biochar application mitigates N losses from these positions. Intact soil cores representing four treatments (IR and BR positions treated with and without biochar) were subjected to weekly leaching events throughout a 100 d laboratory incubation. Soil N2O emissions were measured every 3-4 d and nitrate concentrations in soil solution and leachate were determined weekly. Results indicate that row position strongly affected N2O emissions (daily flux rates were 2.5-fold greater in IR than in BR), but did not affect average nitrate concentrations in soil solution or leachate. Biochar increased daily average N2O emissions in IR by 30%, but decreased them by 39% in BR. However, biochar consistently decreased nitrate concentrations in soil solution and leachate in both row positions by 8-14% and 11-15%, respectively. Findings from this short-term incubation indicate that increased soil N turnover resulting from soil functional zone management practices may increase potential environmental costs due to elevated N2O emissions. In addition, contrary to the majority of previous studies which have not accounted for within-field spatial variability when assessing the N2O mitigation potential of biochar, these results suggest biochar can have contrasting impacts within a field depending on spatial soil management history and C and N cycling processes.