The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 250

TOC-5050 analyser for DOC and dissolved inorganic C, with an Abimed
TN-05 for total N, with ICP-OES (GBC Integra XMP) for total P and S,
and with ion chromatography (Dionex DX-100) for NH 4 + ,NO 3 − ,NO 2 − ,
H 2 PO 4 − and SO 4 2− . DOC, DON, DOP and DOS were calculated by the
difference between the total amounts and the sum of the inorganic forms.
Elements in the hydrophobic fraction were calculated by the difference
between the amounts in the original sample and the hydrophobic fraction.
Sub-samples of soil water collected over each quarter of the year were
pooled. The samples were treated with an acidic cation exchange resin
(BioRad AG MP-50) to remove all cations other than H + , and freeze dried.
Chemical structures of C and P were estimated by liquid-state 13 C- and
31 P-nuclear magnetic resonance (NMR) spectroscopy. For analytical
conditions and designation of signals, see Kaiser et al . (1997) and Sumann
et al . (1998).
Calculation of fluxes
We calculated fluxes of the DOM released from the forest floor into the
mineral soil from the amounts of seepage water sampled using zero-tension
lysimeters beneath the forest floor layer and concentrations therein. Fluxes
in the mineral soil were calculated from porewater concentrations and the
simulated water fluxes. Water flux simulation was carried out using a water
transport model (WHNSIM; Huwe, 1992). Input variables were meteoro-
logical data of the site and the water content-tension relationship of the
soils. Validation of the model was achieved to measured soil water tensions.
Seepage water in sub-soil at rapid flow conditions was sampled using
zero-tension lysimeters. Fluxes were calculated from the amount of seepage
water and concentrations therein.
Results and Discussion
The sampling period was characterized by unusually high rainfall during
autumn 1998 compared with former years. Bulk precipitation peaked at
the beginning of November 1998 with maximum of 204 mm in 10 days
(Fig. 4.4.1). The rainfall during September to November 1998 comprised
50% of the annual precipitation.
The forest canopy was a minor source of DOM. Exceptions were the
times of leaf sprout and before leaf fall (results not shown here). The major
source of DOC, DON, DOP and DOS was the forest floor (Table 4.4.2).
Organic nutrient forms represented up to 85% of the total nutrient content
of the forest floor seepage water and were mainly in the hydrophilic DOM
fraction. This result accords well with the observation of Qualls and Haines