53
selected were the hot/wet and hot/dry scenarios in view of likely increases of temperature while rainfall change direction is uncertain.
5.2.3 Crop Model Setup and Sensitivity Tests
DSSAT and APSIM models were used to test the effects of climate change on crop
production (McCown et al. 1996; Jones et al. 2003; Hoogenboom et al. 2010;
Holzworth et al. 2015). Both DSSAT and APSIM are models that have been developed to simulate biophysical processes in crop farming systems in relation to economic and ecological outcomes of management practices in current or future
farming systems (Hoogenboom et al. 2010; Holzworth et al. 2015; Steduto et al.
2009). For Nkayi the models have been calibrated (Masikati et al. 2014, 2015) and
can be used with confidence in conducting ex-ante climate impact assessments on
crop production systems.
For this study we assess the impacts of single climate factors (CO 2 , temperature
and rainfall) at varying levels (Table 5.1) and also the combined effects on maize
and groundnut. Model simulations were done on three soil types which differed in
soil physical and chemical characteristics (Table 5.2): poor, average and better soils
representing about 29%, 59% and 12% of farms in the district, respectively. Current
farmer management practices were used and these are defined in Table 5.3. Outputs
from the models, which were considered for the current analyses, include grain and
stover crop yields. Planting was set to be done automatically after the model detected
that the set soil moisture conditions were met. For this study the sowing window
was set between 1 November and 31 December, and planting was done when at
least 15 mm of rain was received in three consecutive days.
5.3 Results
5.3.1 Maize Response to CO 2 , Temperature, Rainfall
and Fertilizer
Maize sensitivity to CO 2 was evaluated at different concentrations with 60 kg N/ha
and without nitrogen fertilizer. Without fertilizer, only the APSIM model simulates
slight yield increases in response to increasing CO 2 concentrations on better soils.
However, when fertilizer is added both models simulate increases of maize yields
with increasing CO 2 across all soil types. Maize sensitivity to CO 2 levels differed
between the two models and across soil types (Fig. 5.2). Both maize grain and stover show incremental yields up to the maximum level evaluated here, 720 parts per
million (ppm), which is more than double the current CO 2 levels.
5 Understanding the Role of Soils and Management on Crops in the Face of Climate…
selected were the hot/wet and hot/dry scenarios in view of likely increases of temperature while rainfall change direction is uncertain.
5.2.3 Crop Model Setup and Sensitivity Tests
DSSAT and APSIM models were used to test the effects of climate change on crop
production (McCown et al. 1996; Jones et al. 2003; Hoogenboom et al. 2010;
Holzworth et al. 2015). Both DSSAT and APSIM are models that have been developed to simulate biophysical processes in crop farming systems in relation to economic and ecological outcomes of management practices in current or future
farming systems (Hoogenboom et al. 2010; Holzworth et al. 2015; Steduto et al.
2009). For Nkayi the models have been calibrated (Masikati et al. 2014, 2015) and
can be used with confidence in conducting ex-ante climate impact assessments on
crop production systems.
For this study we assess the impacts of single climate factors (CO 2 , temperature
and rainfall) at varying levels (Table 5.1) and also the combined effects on maize
and groundnut. Model simulations were done on three soil types which differed in
soil physical and chemical characteristics (Table 5.2): poor, average and better soils
representing about 29%, 59% and 12% of farms in the district, respectively. Current
farmer management practices were used and these are defined in Table 5.3. Outputs
from the models, which were considered for the current analyses, include grain and
stover crop yields. Planting was set to be done automatically after the model detected
that the set soil moisture conditions were met. For this study the sowing window
was set between 1 November and 31 December, and planting was done when at
least 15 mm of rain was received in three consecutive days.
5.3 Results
5.3.1 Maize Response to CO 2 , Temperature, Rainfall
and Fertilizer
Maize sensitivity to CO 2 was evaluated at different concentrations with 60 kg N/ha
and without nitrogen fertilizer. Without fertilizer, only the APSIM model simulates
slight yield increases in response to increasing CO 2 concentrations on better soils.
However, when fertilizer is added both models simulate increases of maize yields
with increasing CO 2 across all soil types. Maize sensitivity to CO 2 levels differed
between the two models and across soil types (Fig. 5.2). Both maize grain and stover show incremental yields up to the maximum level evaluated here, 720 parts per
million (ppm), which is more than double the current CO 2 levels.
5 Understanding the Role of Soils and Management on Crops in the Face of Climate…