50
change impacts are projected to reduce yields by up to 25% (Ioras et al. 2014;
Asseng et al. 2015; Rurinda et al. 2015). Agriculture-based livelihood systems that
are already vulnerable to food insecurity will face immediate risk if such yield
reductions would occur. Although there has been progress made to understand the
impact of climate change and variability on different crops in Africa, there is limited
knowledge on how crop-soil systems respond to climate change. Characteristics of
different soils vary; for example, clay soils with high organic matter have low thermal conductivity as well as high water holding capacity (Makinen et al. 2017). In
contrast, sandy soils, which are predominant in smallholder farming systems, have
high thermal conductivity and low water holding capacity (Moyo 2001; Nyamangara
et al. 2001). However, the levels of fertility of sandy soils within and across farms
greatly depend on the soil-fertility management practices used (Tittonell et al. 2007;
Zingore et al. 2011). Soil-climate combination also plays a key role. The magnitude
of crop responses to climate is highly sensitive to the soil type (Folberth et al. 2016;
Makinen et al. 2017). Farmers in Nkayi, Zimbabwe, have already experienced this;
during years of above-average rainfall, farming on clay soils generated a better harvest than on sandy soils, while the reverse is also true.
Empirical and quantitative information regarding the dependency of yield
responses to agro-climatic variables on soil type is needed for designing effective
climate-smart adaptation methods and enhancing the resilience of smallholder
farming systems in the region (Piikki et al. 2015; Folberth et al. 2016; Makinen
et al. 2017). Crop models are important tools that can be used to unravel the importance of soil type on crop responses to climate change and variability. However,
model choice is also important as different model configurations, operation time
steps, physiobiological processes, and others determine the model outputs (Asseng
et al. 2015). Here we use the Decision Support System For Agrotechnology Transfer
(DSSAT) model and the Agricultural Production Systems Simulator (APSIM)
model (McCown et al. 1996; Jones et al. 2003; Hoogenboom et al. 2010; Holzworth
et al. 2015). The two models simulate the dynamics of phenological development,
biomass growth and partitioning, water and nitrogen cycling in an atmosphere-cropsoil system driven by daily weather variables that include rainfall, maximum and
minimum temperatures and solar radiation (Hoogenboom et al. 2010; Holzworth
et al. 2015). We use the two models to (1) assess the sensitivity of maize and groundnuts to individual climatic factors such as rainfall, temperature and CO 2 concentration, under three soil types differentiated by levels of organic carbon and plant
available soil water (2) simulate the combined impacts of future climate (2040–
2070) on the two crops across the three soil types. Both soil fertility and climate are
important issues in smallholder farming systems and will have different impacts on
plant production and crop yields under future climate change. Production may
increase or decrease depending on plant response to the interactions between climate and soil type, hence the importance to assess these impacts to inform adaptation decision-making.
P. Masikati et al.
change impacts are projected to reduce yields by up to 25% (Ioras et al. 2014;
Asseng et al. 2015; Rurinda et al. 2015). Agriculture-based livelihood systems that
are already vulnerable to food insecurity will face immediate risk if such yield
reductions would occur. Although there has been progress made to understand the
impact of climate change and variability on different crops in Africa, there is limited
knowledge on how crop-soil systems respond to climate change. Characteristics of
different soils vary; for example, clay soils with high organic matter have low thermal conductivity as well as high water holding capacity (Makinen et al. 2017). In
contrast, sandy soils, which are predominant in smallholder farming systems, have
high thermal conductivity and low water holding capacity (Moyo 2001; Nyamangara
et al. 2001). However, the levels of fertility of sandy soils within and across farms
greatly depend on the soil-fertility management practices used (Tittonell et al. 2007;
Zingore et al. 2011). Soil-climate combination also plays a key role. The magnitude
of crop responses to climate is highly sensitive to the soil type (Folberth et al. 2016;
Makinen et al. 2017). Farmers in Nkayi, Zimbabwe, have already experienced this;
during years of above-average rainfall, farming on clay soils generated a better harvest than on sandy soils, while the reverse is also true.
Empirical and quantitative information regarding the dependency of yield
responses to agro-climatic variables on soil type is needed for designing effective
climate-smart adaptation methods and enhancing the resilience of smallholder
farming systems in the region (Piikki et al. 2015; Folberth et al. 2016; Makinen
et al. 2017). Crop models are important tools that can be used to unravel the importance of soil type on crop responses to climate change and variability. However,
model choice is also important as different model configurations, operation time
steps, physiobiological processes, and others determine the model outputs (Asseng
et al. 2015). Here we use the Decision Support System For Agrotechnology Transfer
(DSSAT) model and the Agricultural Production Systems Simulator (APSIM)
model (McCown et al. 1996; Jones et al. 2003; Hoogenboom et al. 2010; Holzworth
et al. 2015). The two models simulate the dynamics of phenological development,
biomass growth and partitioning, water and nitrogen cycling in an atmosphere-cropsoil system driven by daily weather variables that include rainfall, maximum and
minimum temperatures and solar radiation (Hoogenboom et al. 2010; Holzworth
et al. 2015). We use the two models to (1) assess the sensitivity of maize and groundnuts to individual climatic factors such as rainfall, temperature and CO 2 concentration, under three soil types differentiated by levels of organic carbon and plant
available soil water (2) simulate the combined impacts of future climate (2040–
2070) on the two crops across the three soil types. Both soil fertility and climate are
important issues in smallholder farming systems and will have different impacts on
plant production and crop yields under future climate change. Production may
increase or decrease depending on plant response to the interactions between climate and soil type, hence the importance to assess these impacts to inform adaptation decision-making.
P. Masikati et al.