Author Dr Amelia Hood describes what their systematic map of cassava farming practices revealed about our knowledge gaps around this important staple crop.

Cassava is a potato-like tuber used to produce a wide array of savoury and sweet dishes, either for direct consumption (e.g. tasty chips!) or following processing into flour (e.g. tapioca, farinha, garri).

Cassava – also known as mandioca and yuca – is a primary food source for many people across the tropics and subtropics, and is regularly consumed by 10% of the global population. It is largely grown by small-scale farmers and eaten locally, with secondary uses as animal feed and biofuel.

Cassava under climate change

Climate change and population growth will significantly increase pressure on global food security this century due to the combined impacts of water scarcity, extreme weather events, biodiversity loss, and pest and disease spread. Sub-Saharan Africa, which produces 50% of cassava globally, is the most vulnerable region to these increasing pressures.

Cassava is a hugely promising crop under climate change as it can keep producing food under drought conditions when other major crops cannot. It can also be grown in soils with low fertility and harvested at any time, which is advantageous when unpredictable climate events alter expected harvesting dates.

Several international authorities on cassava farming, such as the International Center for Tropical Agriculture (CIAT), the International Institute of Tropical Agriculture (IITA) and the UN’s Food and Agriculture Organisation (FAO) have been prioritising and leading cassava research, but large knowledge gaps (understudied topics) remain, and identifying and filling these will be key to optimising sustainable cassava production and creating climate-resilient farming systems.

In our article, we reviewed the research on cassava agriculture by producing a systematic map.

A systematic map of cassava agriculture

A systematic map is a research method used to collate and describe existing literature on a particular topic. Unlike a systematic review, which answers a specific research question (e.g. what is the impact of intercropping cassava on crop yield?), a systematic map identifies and describes existing research on a particular topic (e.g. which studies have investigated the impact of intercropping cassava?). Systematic maps can be used by researchers, funders, practitioners and policy makers to identify relevant research or knowledge gaps requiring further attention.

For our map, we followed a published protocol to identify which studies had measured the impacts of cassava farming interventions (e.g. intercropping/tilling) on agricultural, economic and environmental outcomes (e.g. yield/soil). We assessed which interventions and outcomes were studied where and when, and the quality of the research (e.g. study designs). Interventions and outcomes were developed into new hierarchical ontologies (Agri-ontologies 1.0), which are not described here.

We found 36,580 relevant records and included 1,599 studies in the final systematic map. For anyone unfamiliar with this research method, a systematic map this size takes a long time to build – in our case several years with a team of people!

Cassava research needs greater prioritisation

Our systematic map showed that:

1. Research is clustered, with minimal research in some regions of major production

We found strong clustering of research with 46% of studies conducted in Nigeria, Colombia, and Brazil alone, and 70% of studies conducted over just ten countries.

This partly stems from production, as most major cassava-producing countries are in included in this top ten, but several regions are understudied. For example, the Democratic Republic of Congo is the second highest producer, with only 11 studies, and Ghana, Vietnam, and Indonesia are major producers, each with fewer than 50 studies.

We recommend that researchers and funders urgently target these regions, particularly as average yields in these areas are 60% lower than potential yields (18 T/ha vs 44 T/ha).

2. Majority of research focused on production, with little research into wider impacts

There were large knowledge clusters in terms of the studied interventions and outcomes.

For interventions, most studied interventions related to crop management (70%), and testing different cultivars in particular. Soil, water and crop land management (19%), and non-crop habitat management (e.g. margins) (34%) were studied less.

The most studied outcomes related to crops (58%), and crop yield in particular, with soil (17%), water (2%), pollutants (1.5%) or wildlife (4%) receiving less attention.

Whilst a primary function of agricultural land is to produce food, identifying and implementing best-practice management for the soil, water, and biodiversity will help with this aim by stabilising crop yield fluctuations and promoting resilience to ecological disturbances, such as extreme weather events, in addition to wider societal benefits (e.g. carbon sequestration and water quality). Therefore, we strongly recommend that stakeholders use this systematic map to identify and fill these key knowledge gaps.

3. Poor reporting standards, short-term projects and publication delays are hampering research

Reporting standards refer to the descriptive data that are published to provide the context for a study (e.g. location). We found that reporting standards were poor (e.g. 24% of studies did not report experimental start dates) and recommend that reporting checklists/guidelines are promoted  to  improve this (e.g. AgroEcoList 1.0 for agricultural ecology).

Long-term projects should also be prioritised, as average study duration was two years which is brief for determining ecological impacts that can take years to accrue. We also found that average publication delay (time from experiment end to publication) was four years, which means decision-makers are not getting the most relevant research in a timely manner. Systemic changes are needed across academia to address this (see Christie et al. 2021).

Given the importance of cassava as a staple crop, we urge researchers, funders, policymakers and  other stakeholders to prioritise cassava research, and use our systematic map to identify knowledge clusters for syntheses and knowledge gaps for new experiments.

In particular, we recommend targeting the under-researched regions identified here, and interventions and outcomes related to the soil, water, and biodiversity. This will help to close existing yield gaps, reduce the impacts of cassava production on the wider environment, and promote food security under climate change.

Read the full Stage 2 Registered Report : “A systematic map of cassava farming practices and their agricultural and environmental impacts using new ontologies: Agri-ontologies 1.0” in Ecological Solutions and Evidence.