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Ecological practices such as intercropping maize (Zea mays) with cowpea (Vigna unguiculata L.) have been promoted to combat parasitic weeds like Striga (Striga asiatica). Intercropping has been promoted across Africa as a Striga control practice (SCP) and food security measure. Despite past efforts, millions of smallholder farmers (cultivating < 2 ha of maize) still struggle to implement SCPs. Social and ecological factors that prevent SCP implementation are well documented in the literature, but their underlying interactions have remained elusive. System dynamics modeling can uncover these interactions and assess their effect on intercropping rates as well as Striga emergence. This study presents a participatory mixed methods approach to build a system dynamics model based on two theories: diffusion of innovations and resource pool dynamics. The model estimates the population of fields where Striga emerged in response to intercropped fields when various interventions were implemented. According to model simulations, if new policies are not enacted to support intercropping, Striga is likely to spread to 2,625,000 maize fields, parasitizing almost 75% of smallholder farms across Central Malawi by 2036. The participatory approach allowed us to evaluate several policies, one of which sustained enough adopters to limit Striga emergence to < 500,000 fields, reducing the weed's threat to food security. This policy considers how input costs and erratic rainfall can lead to disadoption, therefore, supporting the implementation of five to six consecutive years of intercropping by providing both fertilizer subsidies and demonstration plots. In this study, our participatory approach has shown to develop a model that can highlight interactions in social ecological systems, their leverage points, and how they can be exploited to develop effective food security policies [ABSTRACT FROM AUTHOR]

In recent years, concerns have grown about increased demand for energy and waste accumulation in Brazil. Technologies that digest waste and capture biogas in the process have been presented as an avenue to address these two issues. Brazil’s biogas potential has been studied extensively, however, less investigation has estimated production across time. A system dynamics model (SDM) was developed to estimate biogas yield over a 30-year period from municipal waste, feedstock, vinasse and waste water routes. The SDM was parameterized using open databases and literature, with a focus on technology diffusion. The analysis indicates production may reach 5.3 million cubic meters/day of methane by 2030 to 19.7 million in 2050. Exchange of information (via word of mouth) exponentially increased technology adoption rates, suggesting that production can be supported by disseminating information that promotes the environmental and economic benefits of transforming biomass into energy. Slow growth was attributed to an absence of policies that incentivized production and its research and development programs. These two hurdles presented challenges for adopters to overcome high upfront costs. Future efforts should focus on the solid waste and feedstock routes given that they assumed the largest production and fast growing population of adopters, respectively. Radical and integrated policies are required to reach substantial biogas yields from four routes to address environmental and energy concerns for Brazil. • Municipal waste has the highest potential to produce biogas. • The feedstock sector will be the fastest biogas production grower in the future. • A national policy before 2025 is advised. • Finding a specific levelized energy cost for biogas is likely to incentivize production. [ABSTRACT FROM AUTHOR]