Influence of reduce tillage on soil organic matter fractions in the surface layer of Belgian silty cropland soils

Reports throughout literature have confirmed that reduced tillage (RT) management may increase the surface soil organic carbon (SOC) and nitrogen (N), particularly by increasing labile organic matter (OM). However, only very few studies have focused on cereal-root crop rotations under a temperate climate which cover a large part of Europe. We investigated the effect of RT on the storage and distribution of SOC and N over different soil fractions in three pairs of RT and conventionally tilled (CT) fields with cereal- root crop rotations located in the Belgium loess belt. Surface soil samples (0-10 cm) were physically fractionated according to a microaggregate- isolation method and a combined ultrasonication-sedimentation particle size fractionation method. RT management was found to be effective in increasing the organic carbon (OC) and N content of the surface soil (0-10cm) at these three sites. Physical fractionation showed that while OC and N in the free particulate OM (POM) can be increased by up to 70% by adopting RT management, only a modest increase in the relative contribution of total POM occurs under these typical Western European arable crop rotations. Indeed, the intra-microaggregate particulate OM (iPOM) accounted for up to 50% of the difference in OC and N in only one of the three pairs of RT and CT fields. In the other two paired fields we measured no accumulation of iPOM. We conclude that the repeated disturbance of soil by harvest of the root crop may limit the accumulation of iPOM under RT management