A meta-analysis and critical evaluation of influencing factors on soil carbon priming following biochar amendment

Abstract

Purpose Previous studies have found biochar-induced effects on native soil organic carbon (NSOC) decomposition, with a range of positive, negative and no priming reported. However, many uncertainties still exist regarding which parameters drive the amplitude and the direction of the biochar priming. Materials and methods We conducted a quantitative analysis of 1170 groups of data from 27 incubation studies using boosted regression trees (BRTs). BRT is a machine learning method combining regression trees and a boosting algorithm, which can effectively partition independent influences of various factors on the target variable in the complex ecological processes. Results and discussion The BRT model explained a total of 72.4% of the variation in soil carbon (C) priming following biochar amendment, in which incubation conditions (36.5%) and biochar properties (33.7%) explained a larger proportion than soil properties (29.8%). The predictors that substantially accounted for the explained variation included incubation time (27.1%) and soil moisture (5.0%), biochar C/N ratio (6.2%), nitrogen content (5.5%), pyrolysis time during biochar production (5.1%), biochar pH (4.5%), soil C content (5.2%), sand (4.7%) and clay content (4.1%). In contrast, other incubation conditions (temperature, biochar dose, whether nutrient was added), biochar properties (biochar C, feedstock type, ash content, pyrolysis temperature, whether biochar was activated) and soil properties (nitrogen content, silt content, C/N ratio, pH, land use type) had small contribution (each < 4%). Positive priming occurred within the first 2 years of incubations, with a change to negative priming afterwards. The priming was negative for low N biochar or in high-moisture soils but positive on their reverse sides. The size of negative priming increased with rising biochar C/N ratio, pyrolysis time and soil clay content, but deceased with soil C/N ratio. Conclusions We determine the critical drivers for biochar effect on native soil organic C cycling, which can help us to better predict soil C sequestration following biochar amendment.

Soil carbon increased by twice the amount of biochar carbon applied after 6 years: Field evidence of negative priming

“…While mechanisms responsible for the accumulation of biogenic soil organic C in the biochar‐amended plots are not yet fully understood, we suggest, based on literature, that time after biochar application, soil textural class, soil water content, biochar pyrolysis temperature, and quality and quantity of initial soil C are potential factors affecting priming (Ding et al, ; Maestrini et al, ; Wang et al, ). For instance, the negative priming effect can increase with an increase in soil water content, biochar pyrolysis temperature, and soil clay content (Ding et al, ). A review of 21 studies, although mostly laboratory studies, concluded that biochar retarded the mineralization of soil organic matter by 3.8% in fine‐textured soils, but it accelerated mineralization of soil organic matter by 20.8% in sandy and low‐fertility soils (Wang et al, ).…”

“…Water content at −33 kPa (cm 3 /cm 3 ) quantity of initial soil C are potential factors affecting priming (Ding et al, 2018;Maestrini et al, 2015;Wang et al, 2016). For instance, the negative priming effect can increase with an increase in soil water content, biochar pyrolysis temperature, and soil clay content (Ding et al, 2018).…”

“…Water content at −33 kPa (cm 3 /cm 3 ) quantity of initial soil C are potential factors affecting priming (Ding et al, 2018;Maestrini et al, 2015;Wang et al, 2016). For instance, the negative priming effect can increase with an increase in soil water content, biochar pyrolysis temperature, and soil clay content (Ding et al, 2018). A review of 21 studies, although mostly laboratory studies, concluded that biochar retarded the mineralization of soil organic matter by 3.8% in fine-textured soils, but it accelerated mineralization of soil organic matter by 20.8% in sandy and low-fertility soils (Wang et al, 2016).…”

Microbial community shifts reflect losses of native soil carbon with pyrogenic and fresh organic matter additions and are greatest in low-carbon soils

“…(Although the term "priming" (14) is widely-used to describe this phenomenon, due to broad interpretations of the term (15), we will refer to "increased or decreased mineralization"; even though less concise, this method-and process-agnostic term will help ensure clarity and avoid prior expectations of what the term "priming" implies.) Research over the past decade has progressed beyond observation of the phenomenon to systematic investigations of the mechanisms underlying these interactions (16)(17)(18), while the conclusions from meta-analyses have strengthened as the total number of studies of PyOM-SOC interactions has steadily increased (19)(20)(21)(22).…”

“…Briefly, current understanding of mechanisms underlying interactive effects of PyOM additions on SOC mineralization includes the following observations (19)(20)(21)(22): (1) In general, when changes in mineralization do occur, net increases in nSOC mineralization tend to be limited to the earlier stages of incubations or field studies, while net decreases in nSOC mineralization often emerge later. (2) It is essential to consider the specific properties of PyOM and the soil to which it is applied together.…”