Angharad Johnston, Adam Muhammad Adam, Charles Spillane
01 February 2025
A recent study, ‘Enhancing the resilience of intercropping systems to changing moisture conditions in Africa through the integration of grain legumes: A meta-analysis’, led by LEG4DEV researcher Adam Muhammad Adam from the University of Hohenheim finds that the integration of grain legumes into cropping systems is an effective strategy to enhance resilience against the effects of climate change. Such strategies are critical in Africa to protect people’s livelihoods and food security but, as Adam et al. highlight, their success depends on a thorough understanding of optimal crop combinations, agronomic practices and the expected climactic and agroecological changes within the current models. Through a meta-analysis of the current literature Adam et al. provide the foundations necessary for stakeholders in southern Africa to begin to adopt, implement and expand legume-based intercropping practices in the region.
“Humanitarian partners are calling on donors to help save lives and protect livelihoods, while enabling communities to build resilience against future shocks”
In May of 2024, in response to the most severe drought in over a century, the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) called for solidarity and assistance from the international community for Southern Africa, sighting widespread food insecurity and acute malnutrition for the more than 61 million people. The countries worst affected included Zambia, Zimbabwe, southern Malawi (among others) where crop production, livestock and water supplies were heavily impacted. OCHA declared ‘Malawi, Zambia, and Zimbabwe, are facing a national disaster with more countries likely to follow’. To compound this, torrential rains from tropical storms caused flooding in Madagascar, Mozambique, Malawi, and Zambia displacing thousands of people and further impacting crop production.
“Despite the considerable literature on intercropping systems, it remains unclear which of the system(s) will perform best under different moisture conditions. Knowledge of moisture availability…has not been addressed in the broader context within the scientific literature”
Farmers in southern Africa often rely on rain-fed agriculture and so are particularly vulnerable to changes in rainfall patterns and the availability of moisture in the atmosphere and the soil. Within the context of the recent acute climactic crises, there is a growing need for stakeholders – farmers, researchers, NGOs and policy makers – to work together to enhance the resilience of crop production systems.
Crop diversification and intercropping (growing more than one crop on the same land at the same time) is an acknowledged practice among African farmers for maintaining yield stability under adverse conditions. But designing a robust intercropping system which can deliver greater stability can be complex and must consider the composition of crop types and their relationship to the agronomic management practices used. And while considerable literature exists for legume-cereal crop combinations, there has been less attention on legume-root and legume-tuber crop combinations. Similarly, there are many research studies focused on high-input systems but fewer on lower-input and rainfed small-holder systems with limited adaptive capacity. Adam et al sought to bridge these gaps by incorporating a range of intercropping performance indicators into their analysis.
Notably, they employed the standardized precipitation evapotranspiration index (SPEI) as an indicator of moisture to examine the impact of different moisture conditions on intercropping performance and resource utilisation. The SPEI is a novel index that utilises both precipitation and evapotranspiration data to provide a comprehensive measure of moisture conditions. Adam et al compared the responses of intercropping systems across 7 moisture classes – extremely dry, severely dry, moderately dry, normal, moderately wet, very wet and extremely wet – using this novel SPEI method.
These ‘responses’ were measured in terms of i) Land Equivalent Ratio (LER) as an indicator for intercropping land saving efficiency compared to sole cropping systems, and ii) Transgressive Overyielding Index (TOI) defined as the ratio of total intercropping yield to the highest sole crop yield of the component species. A LER value greater than 1 indicates high land use efficiency, and a value less than 1 indicates poor land use efficiency when compared to sole cropping systems. Similarly, a TOI value greater than 1 indicates the intercropping system is more productive and a TOI value less than 1 indicates an intercropping system less productive compared to sole cropping systems (of either component species).
Overall, Adam et. al found that integrating legumes with cereals generally enhanced performance in terms of both LER and TOI. Cassava-legume combinations were the most effective under dry conditions. However, the results showed high variability in performance between different crop compositions, planting regimes (including crop density and geometry), agronomic practices (including sowing times and NPK application rates) and soil fertility measures (including soil organic carbon and nitrogen).
Millet and sorghum-based systems for example performed better regardless of moisture when compared to maize. This was attributed to the larger planting distance in millet which “reduces direct light and water competition with legumes, especially in drier conditions”.
In contrast, combining legumes with tuber crops like potatoes ‘is a promising option under wetter conditions, likely because potatoes thrive in elevated, high moisture conditions’. Although Adam et al. also stress “studies of potato + legume systems…were conducted exclusively in high-moisture conditions and elevated locations”, highlighting the need for further context-specific explorations of these complex interactions.
“Promoting legume-based intercropping systems, emerges as a climate-smart agricultural practices with a harmonious blend of benefits in Africa”
Overall, this study indicates that the inclusion of grain legumes into both cereal, root & tuber systems enhances their performance and efficiency under variable moisture conditions. And understanding the impact of agronomic factors including sowing densities, planting patterns and soil fertility management strategies, is equally critical towards system optimisation.
These findings provide the foundations and direction for ongoing EU-funded LEG4DEV research and provide a practical example of the benefit of applying agroecology principles such as connectivity and synergy. Understanding and optimising the connections between crops, climate and agronomy is essential for ensuring system performance and system yield under variable (and perhaps unpredictable) conditions. If we are to protect people’s livelihoods and security against future climate shocks and crises, we must seek to better understand our food systems and the complex interactions within them.