Nānea cover cropping - A locally-sourced native legume for sustainable agriculture in Hawaii

Commodities

Practices

Integration of native plants with agriculture is a nature-based solution that addresses challenges to sustainability. Agronomic cultivation of native plants can deliver greater ecosystem services in comparison to non-native species. In particular, native cover crops  have been shown to enhance biodiversity and improve soil health. These benefits can be realized while providing agronomic benefits that maintain or boost yields, such as nitrogen fixation and weed and pest suppression, potentially reducing costs for growers by reducing demand for expensive imported chemical fertilizers and cover crop seed. Even in fertilized systems, nitrogen provisioning from native cover crops could supplement fertilizer applications – a major costs to Hawaii’s growers that relies on expensive imported fertilizers. Improved management strategies could also bolster the adoption of agroforestry methods, resulting in more climate-smart agricultural practices. However, most native plants have not been evaluated for their potential as a cover crop, particularly in the tropics, and growers instead rely on non-native cover crops that primarily originate from temperate regions.

Niche use by local stakeholders and limited previous scientific study suggest that the indigenous Hawaiian plant nānea (Vigna marina) fixes agronomically significant quantities of nitrogen and can support vigorous cash crop growth without chemical fertilizers. A major barrier to the adoption of this species in Hawaiian agriculture is a lack of documentation of agronomic benefits, no active demonstration plots for growers to experience the cover crop first hand, and a lack of appropriate management practices (e.g. installation protocols).

We will quantify nānea’s contributions to sustainable agriculture by measuring biological nitrogen fixation, soil health indicators, weed and pest populations, and crop yields in cropping systems. Ultimately, growers will make the final decision on which cover crops they utilize, but all suitable species (native or exotic) should be available as possible options with information about all their associated benefits. This project will empower farmers to select cover crops that best align with agronomic goals and personal values. We will compare the performance of nānea to two cover crops commonly implemented currently: a comparable non-native cover crop—perennial peanut (Arachis pintoi)—and a grass control treatment. The evaluations will occur in two Indigenous cropping systems: perennial ‘ulu (breadfruit, Artocarpus altilis) orchards and an annual dryland kalo (taro, Colocasia esculenta) system. We hypothesize that nānea, as a locally adapted native species, will be a more regionally appropriate choice in Hawaii compared to the exotic cover crop in terms of both economic and ecological considerations.

We will analyze and communicate research findings about the benefits of nānea cover cropping to growers and the public through field days at demonstration plots, presentations to grower communities, an extension article, a peer-reviewed journal article, and short educational videos. We aim to improve awareness of the use of native plants within agricultural systems and to provide detailed information for farmer decision-making around the application of nānea as a cover crop. Changes in knowledge or behavior will be assessed through pre/post surveys of outreach efforts.

Research Objective 1: Evaluate Biological Nitrogen Fixation (BNF) in three nānea (Vigna marina) and two perennial peanut (Arachis pintoi) accessions.

Research Objective 2: Quantify agronomic and soil health benefits on nānea cover cropping over two years of production in kalo (Colocasia esculenta) and 'ulu (Artocarpus altilis) cropping systems.

Research Objective 3: Conduct establishment and termination trials of nānea cover crop to compare best-practices.

Education Objective 1: Publish an extension article on nānea cover crop management, costs, and benefits

Education Objective 2: Publish a peer-reviewed scientific article on the outcomes of the role of indigenous cover crops in sustainable agriculture.

Education Objective 3: Create educational videos to outreach, tentatively titled "Local Plants for Local Needs."

Education Objective 4: Increase public awareness through field days, demonstration plots, and additional community outreach