Dias nummer 1

1
Origin and composition of Dissolved Organic C
and N from grass-clover mixtures
Jim Rasmussen and Henning Høgh-Jensen Department
of Agricultural Sciences The Royal Veterinary and
Agricultural University Højbakkegårds Allé 30,
DK-2630 Tåstrup, Denmark E-mail jjrakvl.dk
Background The C and N dynamics in perennial
grass-clover mixtures are not fully understood
although such mixtures dominate temperate
grassland. The co-existence of clover and grass
involves both competition for and transfer of
nutrients between the species. The nutrients may
originate from leaky root systems, from a rapid
turnover of the fine root systems, or from
degradation of more stabile organic material.
The aim of the study is - to determine the origin
of DOC and DON in grass- clover mixtures -
to determine the compo- sition of DOC and DON
from the species - to investigate the transfer
of C and N between grass and clover
Method In a third year grass-clover ley at the
KVL research fields, mezotrons were installed to
a depths of 20, 40 and 60 cm in January 2003. In
June 2004 suction cups will be installed
underneath the mezotrons. In the middle of June
leaf labeling of either grass or clover will be
done using 15N- and 14C urea. At day 3, 7, 14 and
28 after the labeling samples from the leaves of
grass and clover and of the percolating water
will be taken. Samples will be analyzed for
content of 15N and 14C. Attempts will be made to
fractionate DOC and DON in the soil solution in
classes according to molecular weight and
proportion of aromatic compounds. After the
last field sampling mezotrons will be excavated
and the distribution of 15N and 14C between plant
and soil compartments will be determined.
Archived at http//orgprints.org/3542