J. Magid et C. Kjaergaard, Recovering decomposing plant residues from the particulate soil organic matter fraction: size versus density separation, BIOL FERT S, 33(3), 2001, pp. 252-257
A detailed size separation of particulate organic matter (POM) from soils a
mended with straw from Hordeum vulgare or Vicia sativa revealed that the lo
ss of C during the first 56 days of incubation mainly occurred from particl
es >2,000 mum, without a concomitant reduction in the size of these large p
articles. Preliminary studies of POM from non-amended soil had shown that t
he stable heavy (>1.4 g cm(-3)) POM fraction was mainly (>80%) composed of
particles <400 <mu>m, whereas the light fraction was dominated by larger pa
rticles (>80%). Therefore we decided to compare the POM <1.4 g cm(3) with P
OM >400 mum. There was a very close relationship between POM>400 mum and PO
M <1.4 g cm(-3) with regard to amounts of C and N, as well as the appearanc
e of these fractions under the microscope. Similarly there was a close rela
tionship between changes in the C content of the POM fractions and the CO2
respired, and this was also the case when comparing changes in POM-N with n
pt N mineralization. This indicated that the biological activity during dec
omposition was actually localized in the POM. Due to the lighter workload a
nd lower expenditure for reagents in connection with size separation of POM
, we recommend the size separation procedure in connection with studies of
residue decomposition in arable systems.