Biochar is increasingly used in agricultural soils to store carbon, improve soil properties, and support climate mitigation. But agricultural soils are also accumulating another persistent form of carbon: microplastics.
A new review published in Agricultural Ecology and Environment warns that when biochar and microplastics occur together, their combined effects on soil carbon may be more complicated than current carbon accounting methods assume.
"Biochar and microplastics are usually studied separately, but in real agricultural soils they increasingly occupy the same pores, aggregates, mineral surfaces, and microbial habitats," said corresponding author Binbin Hu. "Understanding what happens when these two carbon-rich materials meet is becoming essential for accurately evaluating soil carbon storage and the climate benefits of biochar."
The researchers synthesized evidence on how biochar, microplastics, and native soil organic carbon interact across multiple scales, from individual particle surfaces to soil aggregates, microbial communities, greenhouse gas emissions, and whole-soil carbon inventories.
Biochar can help stabilize soil carbon by promoting aggregation, retaining dissolved organic matter, supporting organo-mineral associations, and influencing microbial processing. Microplastics, however, can reorganize soil pores, alter water and oxygen movement, change the transport of dissolved organic matter, and either stimulate or suppress decomposition depending on their polymer type, shape, concentration, weathering state, and surrounding soil conditions.
When the two materials coexist, the outcome is not necessarily the sum of their individual effects. Emerging evidence suggests that biochar may partly buffer some microplastic-driven disruption, for example by improving aggregation or providing additional sorption surfaces. However, the review cautions that this buffering capacity may weaken as biochar and plastic particles age or as available sorption sites become saturated.
The study also identifies a less visible problem: carbon accounting.
Routine measurements of soil organic carbon may not distinguish among naturally occurring soil carbon, pyrogenic carbon introduced through biochar, and fossil-derived polymer carbon from microplastics. As a result, a soil sample containing plastics could appear to contain more stored organic carbon than it actually does from a climate mitigation perspective.
The researchers estimate that in a 0 to 20 cm agricultural plough layer, microplastic-derived carbon equivalent to 0.1% to 0.5% could contribute roughly 3 to 15 Mg C per hectare to routine carbon measurements if it is not separately identified.
This matters for measurement, reporting, and verification, commonly known as MRV, which is increasingly important for soil carbon projects and carbon removal programs. Counting polymer carbon as newly sequestered soil carbon could create a false-positive signal and potentially lead to over-crediting.
To address the problem, the authors propose an evidence-tiered MRV framework that combines polymer-specific measurements with methods designed to identify pyrogenic carbon and native soil carbon separately.
The review also emphasizes that much of the existing evidence comes from short-term laboratory experiments. Long-term field studies that manipulate both biochar and realistic, weathered microplastics remain scarce.
The authors therefore call for long-term field validation, realistic microplastic exposure scenarios, improved carbon-source separation, and integration of polymer-derived carbon into soil carbon models.
Rather than treating biochar and microplastics as independent components, the study argues that future assessments should view agricultural soils as systems where biogenic, pyrogenic, and synthetic carbon increasingly coexist and interact.
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Journal Reference: Yang Z, Simarani K, Zhang X, Martino AD, Chen Y, et al. 2026. Biochar-microplastic co-occurrence in agricultural soils: interfaces, effects on soil organic carbon, and implications for measurement and verification. Agricultural Ecology and Environment 2: e017 doi: 10.48130/aee-0026-0014
https://www.maxapress.com/article/doi/10.48130/aee-0026-0014
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About Agricultural Ecology and Environment :
Agricultural Ecology and Environment (e-ISSN 3070-0639) is a multidisciplinary platform for communicating advances in fundamental and applied research on the agroecological environment, focusing on the interactions between agroecosystems and the environment. It is dedicated to advancing the understanding of the complex interactions between agricultural practices and ecological systems. The journal aims to provide a comprehensive and cutting-edge forum for researchers, practitioners, policymakers, and stakeholders from diverse fields such as agronomy, ecology, environmental science, soil science, and sustainable development.
