Impact of soil properties on the soil methane flux response to biochar addition: a meta-analysis

Abstract

In an effort to optimize soil management practices that can help mitigate terrestrial carbon emissions, biochar has been applied to a wide range of soil environments to examine its effect on soil greenhouse gas emissions. Such studies have shown that the soil methane (CH4) flux response can vary widely leading to both increase and decrease in CH4 flux upon biochar amendment. To address this discrepancy, multiple meta-analysis studies have been performed in recent years to determine the key factors that may control the direction of CH4 flux upon biochar treatment. However, even comparing across conclusions from meta-analyses reveals disagreement upon which factors ultimately determine the change in direction and magnitude of CH4 flux due to biochar addition. Furthermore, using multiple observations from a single study can lead to misinterpretation of the influence of a factor within a meta-analysis due to non-independence. In this study, we use a multivariate meta-regression approach that allows factor interactions to investigate which biochar, soil, and management practice factors in combination or individually best explain the CH4 flux response in past biochar amendment studies. Our results show that the interaction of multiple soil factors (i.e., water saturation, soil texture, and soil organic carbon content) best explains the soil CH4 flux response to biochar addition (minimum deviance information criterion (DIC) value along with lowest heterogeneity) as compared to all models utilizing individual factors alone. These findings provide insight into the specific soil factors that should be taken into account simultaneously when optimizing the CH4 flux response to biochar amendments and building empirical models to quantitatively predict soil CH4 flux.

Biochar in agriculture – A systematic review of 26 global meta‐analyses

“…In the last 4 years, three major meta‐analyses have been published about biochars’ effect on methane fluxes between agricultural soils and the atmosphere. While Cong et al (2018) found no significant effects of biochar, Jeffery et al (2016) and Ji et al (2018) showed average reduction of methane emissions from flooded soils, though mostly for pot and not for field trials.…”

“…Moreover, the co‐application of N‐fertilizer weakened the measured CH 4 ‐reduction. To investigate the underlying mechanisms and improve prediction of biochar effects on soil‐related CH 4 ‐emissions, Cong et al (2018) did not state overall average effects but argued that the interaction of the following three soil factors: water saturation, soil texture and SOC content explain best the soil CH 4 flux responses reported for biochar additions.…”

“…Many pairwise observations in a meta‐analysis can be non‐independent, for example, because they share the same control in a field study, or they might represent data points from a time series. Only a few number of studies took into account or even mentioned the possibility of non‐independence in their data sets (Cong et al, 2018; Jeffery et al, 2017; Peng et al, 2018; Verhoeven et al, 2017). The selection of criteria for non‐independence was found to be the most important factor leading to different outcomes in meta‐analyses (Hungate et al, 2009).…”

“…The RR, although advantageous because it is very intuitive and can be directly translated to % change, is problematic when there are negative values in the data set. For this reason, some studies chose a different effect size metric, such as the differences between means or the Hedge's d (Cong et al, 2018; Jeffery et al, 2016). These studies could not be directly compared with other studies included in Table 1, but their results are reported as well.…”

Potentials, Limitations, Co-Benefits, and Trade-Offs of Biochar Applications to Soils for Climate Change Mitigation

“…An increasing number of studies assesses the role of biochar as a negative emissions technology, with a quantification of technical, economic, and sustainable large-scale deployment potential [5,14,16,17]. Individual studies focus on different aspects of its production systems and on one or more environmental implication(s), such as the long-term stability and effect on soil organic carbon (SOC) [18][19][20][21], its effect on soil physical and hydraulic properties [22][23][24][25], soil degradation [26,27], agricultural yield [28][29][30][31][32], greenhouse gas balance (GHG) [33][34][35][36][37][38][39][40][41][42][43][44], nitrogen availability and emissions [37][38][39][40][45][46][47], that of phosphorus [48][49][50], biochar's toxicity [51][52][53], remediation potential [54]…”