Microbial necromass reveals how tillage affects soil carbon storage in topsoil vs subsoil

A new study from Jilin Agricultural University shows that adding organic carbon to maize fields increases topsoil carbon storage, but the subsoil responds differently depending on tillage method. In ploughed fields, low carbon input boosted subsoil carbon by 27%, while high carbon input almost eliminated that gain. The key is microbial necromass carbon, the dead microbial matter that becomes stable soil carbon. The research tested no-till and plough tillage with four levels of carbon input including straw and manure. Topsoil benefited consistently from more carbon, but subsoil under plough tillage saw diminishing returns at high carbon levels. The authors suggest that ploughing aerates the soil and speeds up microbial decomposition, reducing the material available for stable carbon formation. This matters for carbon farming and soil carbon credits. More carbon input does not automatically mean more storage across the whole soil profile. Farmers and project developers need to tailor tillage and carbon addition to soil conditions like bulk density and pH. Longer term monitoring is still needed, but the study offers practical guidance for designing management strategies that strengthen both fertility and carbon sinks.