Indirect control of soil texture on decomposition of organic matter by mediation of the soil moisture balance - expansion of a field experiment with the factor soil drainage/capillary rise and 13C-pulse-labelling

Soils function central ecosystem compartments as emitter of greenhouse gases, reservoir of
nutrients and carbon, water and biota. The dynamics of soil organic matter (SOM) are interlinked
with local as well as global biogeochemical cycles and its study is a research topic of high relevance
agriculturally and environmentally. One key determinant of soil microbial activity is soil texture with
enhanced physical protection of OM inside soil aggregates and more chemical stabilization by
organo-mineral association with finer particle size. In biogeochemical models these effects are
mostly accounted for by texture-based qualifiers of kinetic rates of SOM mineralization. This focus
on microscale processes has overlooked that in the field, texture also dominantly determines topsoil
moisture. We argue that textural control on SOM-cycling is strongly effectuated through the
moisture balance. This view is motivated by the observation that in NW-Europe sandy topsoils,
despite of their very low clay content, contain more SOM than silty soils under similar land-use. We
currently produce much-needed high-resolution soil moisture and CO2 flux data from soil textural
field treatments to test if more frequent drying of sandy topsoil leads to a less favourable microbial
habitat compared heavier textured soil. We request support to expand the current field experiment
with additional soil drainage steps, and for more effective and detailed follow-up of substratederived
SOM decomposition.