Cover crops for sustainable agrosystems in the Americas. Chapter 2

Rapid depletion of global fertilizer and fossil fuel reserves, combined with concerns about global warming, have resulted in increased interest in alternative strategies for sustaining agricultural production. Moreover, many farmers are being caught in a vicious spiral of unsustainability related to depletion and degradation of land and water resources, increasing labor and input costs, and decreasing profit margins. To reduce their dependence on external inputs and to enhance inherent soil fertility, farmers, thus, may opt to employ farm-generated renewable resources, including the use of cover crops. However, perceived risks and complexity of cover-crop-based systems may prevent their initial adoption and long-term use. In this review article, we provide a historic perspective on cover-crop use, discuss their current revival in the context of promotion of green technologies, and outline key selection and management considerations for their effective use. Based on reports in the literature, we conclude that cover crops can contribute to carbon sequestration, especially in no-tillage systems, whereas such benefits may be minimal for frequently tilled sandy soils. Due to the presence of a natural soil cover, they reduce erosion while enhancing the retention and availability of both nutrients and water. Moreover, cover-crop-based systems provide a renewable N source, and can also be instrumental in weed suppression and pest management in organic production systems. Selection of species that provide multiple benefits, design of sound crop rotations, and improved synchronization of nutrient-release patterns and subsequent crop demands, are among the most critical technical factors to enhance the overall performance of cover-crop-based systems. Especially under adverse conditions, use of mixtures with complementary traits enhances their functionality and resilience. Since traditional research and extension approaches tend to be unfit for developing suitable cover-crop-based systems adapted to local production settings, other technology development and transfer approaches are required. The demonstration of direct benefits and active participation of farmers during system design, technology development, and transfer phases, were shown to be critical for effective adaptation and diffusion of cover-crop-based innovations within and across farm boundaries. In conclusion, we would like to state that the implementation of suitable policies providing technical support and financial incentives to farmers, to award them for providing ecological services, is required for more widespread adoption of cover crop