55
In response to temperature the two models show divergent results on both maize
grain and stover on poor soil. The APSIM model showed a slight increase for grain
yields and a decrease for stover yields, however, the DSSAT model showed the
opposite. Temperature increase of up to 2 °C would see a slight decrease of grain
yields on poor soils, while the same temperature increase would substantially reduce
grain yields on average and better soils with higher impact on the latter. Both models
show almost no effects of temperature increases on maize stover across soil types.
In response to rainfall, a 25% reduction in rainfall, show yield reductions across
all soil types, however impacts are higher on average and better soils. For example
at 25% rainfall reduction yield losses on poor soils simulated by the APSIM model
are 68 kg/ha, while on the average and better soils are 138 and 487 kg/ha, respectively. Simulated average grain yields for current rainfall are 434, 759 and 2110 kg/
ha for poor, average and better soils, respectively. Conversely rainfall that was
higher than the defined baseline was not beneficial to maize grown on poor soils. On
better soils, maize yield increases were simulated only up to about 25% rainfall
increases but after that there is a yield plateau.
On all soil types maize yields show positive response to increases in fertilizer
application rates. Maize yields reach a plateau at about 60–70 kg N/ha for all soil
types, however, from 30 kg N/ha, the rate of yield increases on better soils is low
compared to the other two soil types. Although increases are simulated across soils
with increasing rates of fertilizer higher yield gains were simulated for poor than the
other two soils at application rate of 30 kg N/ha. Grain yields gains with application
of 30 kg N/ha from base yields simulated by the APSIM model were 1314, 1190 and
466 kg/ha for poor, average and better soils, respectively. The average base yields
were 434, 759 and 2110 kg/ha. Above 60 kg N/ha, there is a yield plateau, meaning
that the water environment at Nkayi becomes the limiting factor to achieving higher
average yield.
5.3.2 Groundnuts Response to CO 2 , Temperature, Rainfall
and Fertilizer
Groundnuts show high response to CO 2 concentrations on all soil types (Fig. 5.3).
The two models show similar trends although yields from the APSIM model are
higher than those simulated by the DSSAT model. Both grain and stover yields
Table 5.3 Treatments used to assess the sensitivity of maize and groundnuts crops to different
climate factors in Nkayi, Zimbabwe
Crop
Treatment
Maize
Maize production under farmer practice (low-input system), average fertilizer
application: 3 kg/ha
a and average manure application: 300 kg/ha
a
Groundnuts Groundnut production under farmer practice, use of low yielding recycled seed
with no fertilizer
a
ICRISAT (2008) and Masikati (2011)
5 Understanding the Role of Soils and Management on Crops in the Face of Climate…
In response to temperature the two models show divergent results on both maize
grain and stover on poor soil. The APSIM model showed a slight increase for grain
yields and a decrease for stover yields, however, the DSSAT model showed the
opposite. Temperature increase of up to 2 °C would see a slight decrease of grain
yields on poor soils, while the same temperature increase would substantially reduce
grain yields on average and better soils with higher impact on the latter. Both models
show almost no effects of temperature increases on maize stover across soil types.
In response to rainfall, a 25% reduction in rainfall, show yield reductions across
all soil types, however impacts are higher on average and better soils. For example
at 25% rainfall reduction yield losses on poor soils simulated by the APSIM model
are 68 kg/ha, while on the average and better soils are 138 and 487 kg/ha, respectively. Simulated average grain yields for current rainfall are 434, 759 and 2110 kg/
ha for poor, average and better soils, respectively. Conversely rainfall that was
higher than the defined baseline was not beneficial to maize grown on poor soils. On
better soils, maize yield increases were simulated only up to about 25% rainfall
increases but after that there is a yield plateau.
On all soil types maize yields show positive response to increases in fertilizer
application rates. Maize yields reach a plateau at about 60–70 kg N/ha for all soil
types, however, from 30 kg N/ha, the rate of yield increases on better soils is low
compared to the other two soil types. Although increases are simulated across soils
with increasing rates of fertilizer higher yield gains were simulated for poor than the
other two soils at application rate of 30 kg N/ha. Grain yields gains with application
of 30 kg N/ha from base yields simulated by the APSIM model were 1314, 1190 and
466 kg/ha for poor, average and better soils, respectively. The average base yields
were 434, 759 and 2110 kg/ha. Above 60 kg N/ha, there is a yield plateau, meaning
that the water environment at Nkayi becomes the limiting factor to achieving higher
average yield.
5.3.2 Groundnuts Response to CO 2 , Temperature, Rainfall
and Fertilizer
Groundnuts show high response to CO 2 concentrations on all soil types (Fig. 5.3).
The two models show similar trends although yields from the APSIM model are
higher than those simulated by the DSSAT model. Both grain and stover yields
Table 5.3 Treatments used to assess the sensitivity of maize and groundnuts crops to different
climate factors in Nkayi, Zimbabwe
Crop
Treatment
Maize
Maize production under farmer practice (low-input system), average fertilizer
application: 3 kg/ha
a and average manure application: 300 kg/ha
a
Groundnuts Groundnut production under farmer practice, use of low yielding recycled seed
with no fertilizer
a
ICRISAT (2008) and Masikati (2011)
5 Understanding the Role of Soils and Management on Crops in the Face of Climate…