soils and reservoirs (Clemens et al. 2010; Schmitter et al. 2010). Farmers in the area
are well aware of the ongoing land deterioration problems, but the adoption rate for
soil conservation techniques is low, as soil conservation measures are either not
known or considered unprofitable (Saint-Macary et al. 2010; Chap. 7).
10.2.4.3 Parameterization, Calibration and Validation of the Model
Pixel size in the Chieng Khoi model was set at 25 by 25 m, which corresponds to the
size of an average smallholder plot. Maize fields in Chieng Khoi are slashed and
burned between November and March; fields are plowed at the start of the wet
season (April to October) and maize is sown in May. The study site was selected as,
in addition to Uplands Program research, field experiments carried out by another
project related to the University of Hohenheim were being carried out in the area,
studying the farmers’ current practices in comparison to low-cost maize cultivation
in which maize fields were not being burned nor tilled but intercropped with
legumes (e.g., Arachis pintoi).
We based our model scenarios on this experiment, comparing farmers’ practices
as a baseline scenario, as compared to the three alternative scenarios, which
included additional management options as defined in Table 10.1 and over a 25
year period. Under these scenarios, we tested the introduction of different soil
conservation options in the maize fields, but not for other crops.
For each scenario, only one management regime was possible across all maize
plots. Three fertilizer levels were implemented, namely zero fertilizer, farmers’
practice (75/50/75 kg elemental N/P/K per hectare) and levels recommended by the
fertilizer manufacturer (double the farmers’ practice). Fertilizer levels per pixel
were not varied between scenarios and years, as the objective of the scenario
building exercise was to compare both model approaches rather than plot-specific
fertilizer levels. Legumes were implemented as soil cover and competition with the
crop for nutrients, as well as biological N fixation were not modeled.
The objective of this experiment was to assess (a) whether soil conservation
measures under maize were able to directly reduce soil degradation and indirectly
reduce it under other land uses on lower slope positions, and if so (b) how far yield
levels would be positively affected by soil conservation measures in the long run.
10.2.4.4 Simulation Results
Firstly, it was found that soil conservation effectively reduced erosion. After the
first year, soil conservation on maize plots under no-tillage (Scenario B) resulted in
0–7.3 Mg ha
À1 less sediment loads per pixel as compared to the Baseline, while the
legume scenarios C and D achieved between 0 and 18.8 Mg ha
À1 less sediment
loads (Fig. 10.6 left). Land uses other than maize showed only minor differences
between scenarios. After 25 years, reduced sediment loads on maize plots reached
up to 365 Mg ha
À1 for Scenario B and 1,680 Mg ha
À1 for Scenario C and Scenario
380
C. Marohn et al.
are well aware of the ongoing land deterioration problems, but the adoption rate for
soil conservation techniques is low, as soil conservation measures are either not
known or considered unprofitable (Saint-Macary et al. 2010; Chap. 7).
10.2.4.3 Parameterization, Calibration and Validation of the Model
Pixel size in the Chieng Khoi model was set at 25 by 25 m, which corresponds to the
size of an average smallholder plot. Maize fields in Chieng Khoi are slashed and
burned between November and March; fields are plowed at the start of the wet
season (April to October) and maize is sown in May. The study site was selected as,
in addition to Uplands Program research, field experiments carried out by another
project related to the University of Hohenheim were being carried out in the area,
studying the farmers’ current practices in comparison to low-cost maize cultivation
in which maize fields were not being burned nor tilled but intercropped with
legumes (e.g., Arachis pintoi).
We based our model scenarios on this experiment, comparing farmers’ practices
as a baseline scenario, as compared to the three alternative scenarios, which
included additional management options as defined in Table 10.1 and over a 25
year period. Under these scenarios, we tested the introduction of different soil
conservation options in the maize fields, but not for other crops.
For each scenario, only one management regime was possible across all maize
plots. Three fertilizer levels were implemented, namely zero fertilizer, farmers’
practice (75/50/75 kg elemental N/P/K per hectare) and levels recommended by the
fertilizer manufacturer (double the farmers’ practice). Fertilizer levels per pixel
were not varied between scenarios and years, as the objective of the scenario
building exercise was to compare both model approaches rather than plot-specific
fertilizer levels. Legumes were implemented as soil cover and competition with the
crop for nutrients, as well as biological N fixation were not modeled.
The objective of this experiment was to assess (a) whether soil conservation
measures under maize were able to directly reduce soil degradation and indirectly
reduce it under other land uses on lower slope positions, and if so (b) how far yield
levels would be positively affected by soil conservation measures in the long run.
10.2.4.4 Simulation Results
Firstly, it was found that soil conservation effectively reduced erosion. After the
first year, soil conservation on maize plots under no-tillage (Scenario B) resulted in
0–7.3 Mg ha
À1 less sediment loads per pixel as compared to the Baseline, while the
legume scenarios C and D achieved between 0 and 18.8 Mg ha
À1 less sediment
loads (Fig. 10.6 left). Land uses other than maize showed only minor differences
between scenarios. After 25 years, reduced sediment loads on maize plots reached
up to 365 Mg ha
À1 for Scenario B and 1,680 Mg ha
À1 for Scenario C and Scenario
380
C. Marohn et al.