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At the end of the annual horticultural production cycle of greenhouse-grown crops, large quantities of residual biomass are discarded. Here, we propose a new value chain to utilize horticultural leaf biomass for the extraction of secondary metabolites. To increase the secondary metabolite content of leaves, greenhouse-grown crop plants were exposed to low-cost abiotic stress treatments after the last fruit harvest. As proof of concept, we evaluated the production of the flavonoid rutin in tomato plants subjected to nitrogen deficiency. In an interdisciplinary approach, we observed the steady accumulation of rutin in young plants under nitrogen deficiency, tested the applicability of nitrogen deficiency in a commercial-like greenhouse, developed a high efficiency extraction for rutin, and evaluated the acceptance of the proposed value chain by its key actors economically. On the basis of the positive interdisciplinary evaluation, we identified opportunities and challenges for the successful establishment of horticultural leaf biomass as a novel source for secondary metabolites., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

A transition towards a bio-based economy is accompanied by a growing demand for biomass resources as fossil fuels need to be replaced for the more sustainable production of consumer goods, chemicals and energy. To increase the supply of renewable biomass and avoid a conflict with food production, currently underutilized by-products (i.e. leaves, stems) from horticultural production could be valorised as feedstock. The success of this approach depends on farmers' willingness to adopt novel practices like the collection and treatment of plant leaves. However, literature on factors influencing farmers' decisions to adopt novel practices aimed to foster the Bioeconomy is limited. This paper addresses this gap by exploring drivers of farmers' interest in the valorisation of by-products. To this aim, the Value-Belief-Norm theory was used and expanded by contextual factors, such as the perceived market demand for biomass and future environmental policies. A survey with German fruit and vegetable farmers (N = 96) has been carried out and data have been analysed with a Structural Equation Model. Findings suggest that the Value-Belief-Norm theory is a relevant framework for the agricultural domain to predict farmers' interest in the valorisation of horticultural by-products. Results further indicate that an internal ecological worldview is potentially relevant for farmers' perception of contextual conditions aimed to foster the Bioeconomy. These outcomes could have managerial and policy implications associated with the identification of potential lead users to trigger the diffusion of innovative sustainable practices and generally foster the Bioeconomy., (Copyright © 2018 Elsevier Ltd. All rights reserved.)