Subsurface soil carbon and nitrogen losses offset surface accumulation
in abandoned agricultural fields
Abstract
Abandoned agricultural fields are thought to accumulate soil organic
matter after cultivation cessation. Most research on soil C and N
sequestration has focused on the surface and overlooked their dynamics
below 30 cm. With 13-year long-term surveys of 21 old field, we found
soil C and N accumulated by 30.5 ± 6.5 g C m⁻² yr⁻¹ and 2.41 ± 0.49 g N
m⁻² yr⁻¹ in the surface (0-20 cm) yet decreased by 64.6 ± 12.5 g C m⁻²
yr⁻¹ and 6.83 ± 1.34 g N m⁻² yr⁻¹ in the subsurface (20-100 cm). Such C
and N losses in subsurface soil can be attributed to the shallow root
distribution, which is likely caused by the continuing dominance of
non-native and shallow rooted C3 grasses and the lack of legumes after
abandonment. Thus, vegetation changes are a legacy effect of agriculture
that leads to ongoing soil C losses in abandoned agricultural fields.