Modelling Soil Organic Matter Dynamics – Global Challenges - Sustainable Management of Soil Organic Matter - page 48

Table 2.1.1. Changes in SOC stocks and CO 2 emissions offsets for the area of central Hungary.

Regression Roth-C model CENTURY model

SOC
change,
Tg

% annual
emissions
offset

SOC
change,
Tg

% annual
emissions
offset

SOC
change,
Tg

% annual
emissions
offset Scenario

Afforestation 101.8 21.66 37.00 8.00 55.00 12.00

No till 44.77 9.52 — — — —

Organic manures a 20.00 4.26 — — — —

Sewage sludge b 131.25 27.93 — — — —

Cereal straw c 46.44 9.88 — — — —

Ley-arable d 62.55 13.31 — — — —

All scenarios applied to all arable land. Annual application rates: a 10 t ha − 1 ; b 2.59 t ha − 1 ;
c 5.07 t ha − 1 ; d 30% ley arable rotation.

study area. We used 1990 CO 2 emissions since 1990 is the Kyoto protocol
baseline.
Finally, we investigated the sustainability of SOC stocks for a typical
arable polygon of the case study area in our GIS database using the
CENTURY model. We ran the model for 3000 years under native forest,
then 350 years extensive arable agriculture and 100 years (1860-1960)
intensive arable agriculture with the inorganic N fertilization rate set at
1960 levels (the earliest statistic from FAOSTAT, 1999). From 1960 to the
present day, the model was run under intensive arable agriculture with
annual N application rates set from FAOSTAT, and finally for a 100 year
scenario of intensive arable agriculture with N application rates at the
current level.

Results and Discussion

There was good agreement between measured and simulated SOC levels at
the validation sites ( r 2 = 0.83). The results of the model comparison and
the regression estimates for the various scenarios are given in Table 2.1.1.
For our demonstration scenario of afforestation of all arable land, SOC
changes predicted using the regression method are significantly greater
than those predicted using the Roth-C or CENTURY models, and the
CENTURY model predicts a greater C sequestration estimate than
Roth-C. Although some of these scenarios are unrealistic and require
refinement for the study area, the magnitude of CO 2 emissions offsets
indicated is encouraging.
Figure 2.1.2 shows the dynamics of SOC predicted by the CENTURY
model for our investigation of SOC stock sustainability. Under native forest