Modelling Soil Organic Matter Dynamics – Global Challenges - Sustainable Management of Soil Organic Matter - page 55

metre of ~12 kg within 100 years, which is ten times better then the
sequestration of carbon in soil.
The range of optimal content of decomposable carbon, published by
Körschens (1999), shows a tendency for higher values in soils with a lower
turnover activity. This leads to the assumption that the turnover rate of
SOM could be a good indicator for SOM management. This is also
reasonable because an increase in the SOM level increases the nitrogen
mineralization and could also increase the nitrogen surplus. Results from
the long-term experiment at Bad Lauchstädt (Körschens et al ., 1994)
suggest that the optimal SOM level for nitrate recovery is 1.97% C org
(Fig. 2.2.1), which is equivalent to a decomposable carbon content of
0.42% and an annual carbon turnover of ~90 g m −2 . Using these values as
a benchmark, possible ranges for the evaluation of the SOM level are
presented in Table 2.2.1.
Results and Discussion
The steady increase in yields - especially after 1989 when agricultural tech-
nology improved very rapidly - leads to a continuous increase in SOM with
some fluctuations due to yield decreases in years with very low precipitation
Fig. 2.2.1. Efficiency of the nitrogen usage (N eff ) as the relationship between N uptake and N
input from mineral fertilizer and manure for 16 different treatments of the Bad Lauchstädt long-term
experiment in term of dependence on the corresponding content of soil organic carbon (C org ). Data
after Körschens et al. (1994).