Farming in semi-arid sub-Saharan Africa (SSA) takes place under harsh agroecological conditions: low and unpredictable rainfall, high temperatures, high climatic variability, low soil fertility, land degradation, attacks of pests and diseases and weed infestation (Arslan et al., 2014; Rurinda et al., 2015). Whilst global agricultural production will need to increase by about 70 – 100% by 2050 to feed the increasing population, van Ittersum et al. (2016) suggested that in the case of SSA the average cereal demand will increase by about 335%. DK1 This means that if SSA is to be food self-sufficient in the future, drastic measures must be applied on existing cropland and/or through expansion of land under cultivation where possible (Chamberlin et al., 2014). In southern Africa, climate change is predicted to have a negative impact on agriculture with more frequent and prolonged droughts and higher temperatures threatening the region’s crop production potential and increasing the vulnerability of smallholder farming households (FAO, 2010). As such, current cropping systems in southern Africa need to be more resilient to the negative effects of climate change.
The problem of low soil fertility and land degradation is exacerbated by the limited use of external nutrient inputs. Efforts to address input use (especially of fertiliser) in SSA have repeatedly found a nexus between climate variability, farmers’ risk perception and on-farm investment (Cooper et al., 2008). Poor soil fertility and access to nutrients remain a protracted problem for smallholder agriculture in SSA (Mupangwa et al., 2013). Although fertiliser use in the region is low, where applied its use efficiency remains low DK2 owing to poor crop management practices. There are different responses to nutrient application as a result of the predominance of sandy soils of inherently low fertility (Bationo et al., 2012) and unbalanced blanket fertiliser recommendations that do not address the complexity of smallholder farming systems (Giller et al., 2011; Chikowo et al., 2015; Njoroge et al., 2017). Nitrogen (N) is inherently deficient in the soils in this region and therefore its management is key for the sustainability of any cropping system in an effort to achieve food security (Sanchez, 2002; Morris, 2007).
1.1.Climate smart agriculture and sustainable intensification approaches
To achieve global food and nutrition security in the face of climate change, two approaches have been proposed in recent times climate smart agriculture (CSA) and sustainable intensification (SI). CSA interventions are defined by their ability to deliver on three fundamental aspects: a) adaptation to the effects of climate change, therefore building resilience into the system; b) provision of mitigation benefits in terms of greenhouse gas emission reduction and building carbon (C) stocks (both above and below ground) and c) improved reliability, sustainability, productivity and profitability of agricultural production systems (Campbell et al., 2014; Lipper et al., 2014). SI approaches entail increasing food production from existing farmland in ways that have lower environmental impacts and which do not undermine our capacity to continue producing food in the future (Godfray et al., 2010). The two concepts, SI and CSA, are complementary with the main difference being that CSA focuses on outcomes related to climate change adaptation and mitigation (Campbell et al., 2014). SI, however, is crucial to both adaptation and mitigation.
Conservation agriculture and legume technologies such as intercropping have been put forward as promising options to achieve both CSA and SI (Pretty et al., 2011; Campbell et al., 2014; Ollenburger and Snapp, 2014; Vanlauwe et al., 2014a; Falconnier et al., 2016; Droppelmann et al., 2017; Thierfelder et al., 2017). The effective application of both cropping systems, as reported in these studies, results in increased food production per unit of input and land, while maintaining or rebuilding soil fertility in the face of a changing climate.
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