Biochar and straw application reshape organic carbon pool via altering soil carbon pump function based on a decadal field experiment

Abstract

Soil organic carbon (SOC) accumulation is critical for maintaining agricultural production and combating climate change. Although organic amendments are commonly applied to improve SOC, the decadal-scale pathways controlling carbon sequestration remain largely unstudied. Here, a 14-year field experiment was utilized to investigate how biochar (BC) and maize straw (SW) regulate soil carbon pumps to impact SOC sequestration. The results showed that BC appeared to improve the efficiencies of both soil microbial carbon pump (MCP) via increasing microbial necromass carbon (MNC) in particulate organic matter (POM) (+90 %) and silt and clay fraction (SCF) (+35 %) and mineral carbon pump (MnCP) via increasing organic carbon (OC) in mineral-associated fractions (including SCF) (+104 %, namely 8.21 Mg C ha⁻¹). Thus, BC enhanced SOC sequestration (+112 %) and promoted field crops growth (+10 %). The higher contribution of the SCF to SOC sequestration in the BC soil was attributed to its reducing carbon output potential, high accumulation of BC and amorphous Fe oxides, and increased Fe-bound OC. In contrast, SW only enhanced MCP operation by mainly promoting MNC concentration on POM (+151 %), which sequestrated SOC (+33 %) and increased crop yield (+7 %). While the low efficiency of MnCP in SW soil resulted from the more mineralization of abundant MNC and less Fe-bound OC within the SCF. A conceptual framework was presented whereby BC could drive both the MnCP and the MCP, resulting in significant potentials for SOC sequestration. Our findings offer valuable insights for optimizing agricultural management strategies to regulate SOC turnover and increase SOC sequestration.