Impact story

Closing cycles in greenhouse horticulture

Cultivating vegetables and fruits in greenhouses is to become circular in every aspect. But how? Wageningen researchers mapped the materials streams and identified opportunities to close these cycles.

Greenhouse horticulture is an innovative sector that yields high-quality vegetables, fruits, and plants and efficiently uses resources. Take, for example, the recirculation of water and fertilisers in greenhouses. Still, the production chains are mainly linear rather than circular. The greenhouse sector depends on natural resources that are located across the planet. Natural gas for energy and CO2, for example. Phosphate (P) and potassium (K) are mined to produce fertilisers. Basalt and peat are needed for substrate and crude oil for plastics. To date, knowledge on how a circular greenhouse and supplier management should be designed was lacking.

Fundamental research to generate support

A multidisciplinary team of fourteen Wageningen University & Research (WUR) scientists mapped six primary material flows to determine what flows into the greenhouse and what comes out. This data helps transition towards circular business management, says project leader Alexander Boedijn. Data visualisations show growers and policymakers the main opportunities and bottlenecks. This fundamental knowledge bridges the gap between reality and future government policy.

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The scope and costs of this transition for the sector are still largely unknown. The data sets and a substantiated future scenario aim to increase support and awareness. Horticulturists do not oppose a circular approach, says Erik van Os. They do, however, lack practical tools. Wageningen researchers successfully worked on recycling water and fertilisers between 1995 and 2015, resulting in a reduction of more than half.

Transition scenarios outline the future

Researchers detail what adjustments are required for circular growth in the future using transition scenarios. These include the viability of so-called crossovers. In crossovers between greenhouse horticulture and fish farming, researchers study to what extent fish faeces may replace mineral fertilisers. Water streams can also be exchanged between fish farms and greenhouses, resulting in increased efficiency for both. In another project, scientists study the exchange of material flows between pig farms and greenhouses. Excess manure from the pig farms to fertilise greenhouses, for example, or green waste from the greenhouse to feed the pigs.

This fundamental research is reaching completion and has already yielded a wealth of follow-up studies. Examples include studies on replacing mineral fertilisers with organic, circular fertilisers. Sometimes small, simple solutions are highly effective. Biodegradable clips were introduced in the cultivation of tomatoes and bell peppers. If biodegradable string is used as well, the crop can be easily chopped and composted. This also helps reduce the amount of plastic. By introducing practical solutions such as these and translating fundamental research into transition scenarios, Wageningen scientists contribute to circular greenhouse horticulture.