Study shows how tillage and carbon inputs affect soil carbon storage differently in topsoil vs subsoil

A new study from Jilin Agricultural University reveals that adding organic carbon to maize fields increases soil organic carbon in topsoil, but the effect on subsoil is more complex. Under plough tillage, low carbon input improved subsoil carbon storage by 27%, while high carbon input reduced that benefit to almost nothing. The key factor is microbial necromass carbon, which behaves differently depending on soil depth and tillage method. The research tested no-tillage and plough tillage with four levels of carbon input in Jilin Province, China. Topsoil carbon increased consistently with more carbon, but subsoil carbon storage depended on how tillage affected microbial activity. Plough tillage aerates the soil, which can stimulate microbes to decompose fungal necromass before it becomes stable carbon. This means more carbon input does not automatically mean more carbon storage across the whole soil profile. For farmers and land managers, the takeaway is that carbon management must be tailored to soil depth and tillage practice. Adding organic amendments on top of straw return helps topsoil, but subsoil carbon sequestration may require adjusting tillage based on existing soil organic carbon, bulk density, and pH. Longer term monitoring is still needed, but the study offers practical guidance for improving agricultural carbon sinks.