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Toward a Better Assessment of Biochar–Nitrous Oxide Mitigation Potential at the Field Scale
Author(s) -
Verhoeven Elizabeth,
Pereira Engil,
Decock Charlotte,
Suddick Emma,
Angst Teri,
Six Johan
Publication year - 2017
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2016.10.0396
Subject(s) - biochar , environmental science , yield (engineering) , nitrous oxide , fertilizer , weighting , chemistry , pyrolysis , environmental engineering , environmental chemistry , mathematics , materials science , organic chemistry , metallurgy , medicine , radiology
Through meta‐analysis, we synthesize results from field studies on the effect of biochar application on N 2 O emissions and crop yield. We aimed to better constrain the effect of biochar on N 2 O emissions under field conditions, identify significant predictor variables, assess potential synergies and tradeoffs between N 2 O mitigation and yield, and discuss knowledge gaps. The response ratios for yield and N 2 O emissions were weighted by one of two functions: (i) the inverse of the pooled variance or (ii) the inverse of number of observations per field site. Significant emission reductions were observed when weighting by the inverse of the pooled variance (−18.1 to −7.1%) but not when weighting by the number of observations per site (−17.1 to +0.8%), thus revealing a bias in the existing data by sites with more observations. Mean yield increased by 1.7 to 13.8%. Our study shows yield benefits but no robust evidence for N 2 O emission reductions by biochar under field conditions. When weighted by the inverse of the number of observations per site, N 2 O emission reductions were not significantly affected by cropping system, biochar properties of feedstock, pyrolysis temperature, surface area, pH, ash content, application rate, or site characteristics of N rate, N form, or soil pH. Uneven coverage in the range of these predictor variables likely underlies the failure to detect effects. We discuss the need for future biochar field studies to investigate effects of fertilizer N form, sustained and biologically relevant changes in soil moisture, multiple biochars per site, and time since biochar application. Core Ideas Biochar reduced mean N 2 O emissions by 12.4% when weighted by the inverse of the pooled variance. Biochar did not significantly reduce N 2 O emissions when weighted by the inverse of the number of observations per site. The effect of weighting function suggests site‐dependence and dataset limitations on the potential of biochar to mitigate N 2 O. Biochar increased yield for both weighting functions.