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Carbon turnover in aggregated soils Bettina
John1, Tamon Yamashita1, Bernard Ludwig2, Heiner
Flessa1 1Institute of Soil Science and Forest
Nutrition, University of Göttingen 2Department of
Environmental Chemistry, University of
Kassel www.gwdg.de/bjohn, bjohn_at_gwdg.de
Table 1 Soil properties of Rotthalmünster, soil
acidified with HCl
Introduction The turnover of soil organic carbon
(SOC) depends on its position in the soil. The
scope of our study is to investigate the
significance of aggregate formation on the
stabilization of SOC depending on fertilization
and land use. We aim to determine the turnover
of carbon in density and size fractions of the
soil by means of 13C measurements and subsequent
calculation of maize-derived percentages.

• Rotthalmünster Soil properties
• Maize-derived percentages of the SOC at
  Rotthalmünster were about 35 (Table 1). This
  higher enrichment of maize-derived SOC as
  compared to the maize-NPK site of the Ewiger
  Roggen at Halle, where after 39 years only 14.0
  of the C were maize-derived was due to its
• higher production of biomass
• input of plant residues after harvest
• high percentage of silt and clay.

• Density fractionation at Halle
• Method Density fractionation of bulk soil (lt
  2mm) from maize and rye sites (Fig. 1 4).
• FPOM free particulate organic matter ?
  between aggregates
• OPOM occluded particulate organic matter ?
  inside aggregates.
• Results
• Partioning of SOC among density fractions
• Mineral (68-75) gt OPOM1.6-2.0 g/cm³ (11-21) gt
  FPOM (6-10) gt OPOMlt 1.6 g/cm³ (2-4.4)
• Maize-derived C in SOC (Fig. 3) FPOM gt
  OPOM1.6-2.0 g/cm³ gtOPOMlt 1.6 g/cm³

Fig. 1. Density fractionation with sodium
polytungstate solution

• Combined size and density fractionation at
  Rotthalmünster
• Method
• 1. Size fractionation of aggregates (Fig. 2)
• 2. Density fractionation for each aggregate class
  (Fig. 1)
• 3. Sieving (53 µm) of the mineral fraction.
• Results
• Tillage destroyed aggregates gt 1 mm which contain
  the major part of SOC of forest and grassland
  soil.
• Aggregates protect carbon from decomposition as
  carbon content in all aggregate fractions 53 µm
  was higher than in the silt clay fraction (lt53
  µm) (Fig. 5).

Fig. 3 Maize-derived C in density
fractions of bulk soil from Halle (means and SE,
n4)
Fig. 2. Combined size and density fractionation
FPOM (lt1.6 g/
cm³
)
OPOM (lt1.6 g/
cm³
)
OPOM (1.6-2.0 g/
cm³
)
Fig. 5 Distribution of C in 100 g soil among
aggregate fractions of Rotthalmünster (means and
SE, n4)
Fig. 4 Density fractions from Halle