Vermicompost enhances the amendment efficacy of biochar in severely saline-alkaline soil through biological reinforcement

Abstract

Coastal saline-alkali soils challenges global agricultural through high salinity, structural degradation, microbial dysfunction, and nutrient depletion. While biochar improves these soils’ physicochemical properties, its capacity to modulate soil microbial communities remains constrained. Therefore, we conducted a soil column experiment to investigate whether vermicompost, as a microbial inoculant can enhance biochar’s remediation efficacy in severely saline-alkali soils through biological reinforcement by enriching functional microbes capable of colonizing and interacting with biochar. Our results revealed that biochar incorporation significantly increased soil organic matter (+180.5%) and other nutrients compared to CK, with further enhancement via synergistic interactions with vermicompost. The vermicompost-supplemented biochar amendment treatment increased water-stable macroaggregates by 20.2% (approximately 2.2 times higher than the sole biochar treatment). The addition of biochar significantly reduced Na⁺, Cl⁻, HCO₃⁻ and SO₄²⁻, but resulted in a decrease in Mg²⁺ and Ca²⁺, while the presence of vermicompost could slow down this trend. Notably, the biochar-vermicompost co-application significantly affected soil bacterial communities by enriching microorganisms associated with carbon and nitrogen nutrient cycling, such as Filobacillus and Xanthobacteraceae. Taken together, these findings indicate that the biochar-vermicompost co-application reduced salt leaching and improves nutrient retention via soil aggregation restructuring, and further remediated saline-alkaline soils by boosting functional microbial communities.

Graphical abstract

Keywords

vermicompost / biochar / severely saline-alkaline soil / organic amendments

Highlight

	● Biochar ameliorated soil properties and reduced salinity in saline-alkali soil.
	● Vermicompost improved biochar-induced macroaggregate formation in severely saline-alkali soil.
	● Vermicompost-supplemented biochar amendment further enhanced salt ion leaching.
	● While vermicompost-supplemented biochar amendment retained divalent cations.
	● Vermicompost microbe-enhanced biochar ameliorated soil microbial community.
	● Vermicompost enhanced biochar’s remediation efficacy in severely saline-alkali soils via bioaugmentation.

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