Greenhouse horticulture is an innovative sector that efficiently uses resources to produce high-quality vegetables, fruits and plants. Still, the total supply chains are often linear, not circular. For resources, greenhouse horticulture, like many other sectors, depends on raw materials that come from natural reserves located all over the world. Think for instance of natural gas for energy, CO2 and the production of nitrate fertilizers. Or phosphate rock (P) and potash (K) extracted from mines to produce fertilizers. Basalt and peat for substrate. Crude oil for plastic. This report contains an overview of the various challenges and possible transition pathways towards closed resource cycles of six typical material flows in greenhouse horticulture; water, fertilizers, CO2, substrate, plastics and biomass. The knowledge developed for and available through this report is part of the Knowledge Base Research Programme: Circular and Climate Neutral that is funded by the Ministry of Agriculture, Nature and Food Quality. The Business unit Greenhouse Horticulture of Wageningen University & Research has conducted the research project (KB-34-007-007) that focuses on the transition towards a circular greenhouse horticulture sector, of which this report is a deliverable.

In a USDA-organic soilless cultivation of tomato organic nitrogen is used as N fertiliser, which needs to be converted to crop available nitrogen by microorganisms around the plant roots. VitalFluid developed a technology that produces nitrogen fertilisers in a natural way in a reactor, using only air, water and electricity (‘Natural nitrogen’; HNO3). Implementation of this nutrient source in a USDA organic soilless nutrient solution is investigated in a cultivation trial. A comparison is made between this ‘natural nitrogen’ nutrient solution and a standard USDA organic nutrient solution (reference). The trial has shown that ‘Natural nitrogen’ can be implemented in a nutrient solution and has advantages over organic nitrogen sources. In the reference treatment, the microbial conversion of organic N had a slow start, so that NaNO3 needed to be applied to have enough readily available nitrogen for the crop to grow. This made it impossible to recirculate drain water in the reference treatment due to increased sodium levels (less K available), whereas the treatment with ‘Natural nitrogen’ could recirculate all drain water. Product quality and productivity of the crop were good in the ‘Natural nitrogen’ treatment, but due to the difficult start of the reference could not be compared to this reference treatment. It is also shown that ‘Natural nitrogen’ as source of N in USDA organic cultivation opens the way to adopting a closed-looped irrigation system. The technology can therefore enlarge the resource use efficiency (RUE) of such a system.

Diverse vegetable production systems are an essential part of European food production. Nitrogen (N) fertiliser and commonly irrigation are integral to European vegetable cropping. Applications of N and irrigation are generally based on the experience of growers and technical advisors. Commonly, applications of both exceed crop requirements causing nitrate (NO3−) leaching. This can result in NO3− contamination of underlying aquifers, which can also contribute to eutrophication of natural surface water bodies. Various agronomic characteristics of vegetable crops such as shallow roots, low density planting and multiple cropping exacerbate the risk of NO3− leaching. Because of health and environmental concerns related to NO3− contaminated groundwater and eutrophication, there is appreciable and increasing societal pressure to reduce these environmental impacts. Additionally, there is increasing societal pressure to reduce emissions of phosphorus and plant protection products to water bodies. The European Union (EU) has passed several Directives to reduce contamination of water bodies from agriculture. Member States of the EU are required to comply and implement these legislations. European consumers are increasingly concerned that their food is produced with minimal environmental impact. Product certification schemes, with requirements or recommendation for N and irrigation management, are required in order to sell vegetables through many European supermarket chains. Because of legislative and consumer pressure, European vegetable growers will increasingly need to adopt science-based management approaches to reduce contamination of water bodies from their farming operations. The virtual Special Issue “Reducing contamination of water bodies from European vegetable production systems” consists of eight review papers that revise the options available to European vegetable growers. The issues facing particular European vegetable production systems are also addressed.

In large parts of the Netherlands surface water quality does not meet the chemical and ecological standards as indicated by the EU Water Framework Directive (WFD). The largest exceedances were found in areas with greenhouse horticulture, flower bulbs, fruit trees and ornamental trees. Several regulations have been implemented to improve water quality in greenhouse areas, leading finally to a target for zero emission of nutrients by 2027 in soilless cultivation and rules to minimise losses in soil bound cultivation. In addition to that an obligation exists to remove plant protection products (PPPs) from drain water by 2018 onwards. For soilless cultivation a Zero Liquid Discharge (ZLD) system gives the best options to reach these goals. For soil-bound cultivation the situation is more complicated and a combination of tools and measurements to help the farmer to tune irrigation to crop demand is most promising. These approaches will lead to a substantial decrease in losses of nutrients and PPPs to surface water. However, it is uncertain whether this will lead to the desired reduction in emissions and the water quality standards of the WFD in 2027. Obstacles might be problems with soil-bound cultivation, leakages in soilless cultivation and sodium limitations in certain crops.

In this project, solutions are developed to minimise leaching of nutrients and pesticides from greenhouses to the environment (esp. surface water), in order to comply with legislation and societal demands. In 2017 the following questions have been addressed: To prevent emission, drain solutions are reused or purified. Other water flows may deviate in compositionand possibilities for reuse or purification. The option for reuse or purification for these water flows has been investigated, and a working methodology for the end of a cultivation (e.g. cleaning) has been developed. Applications of Forward Osmosis in horticulture have been investigated. Water extracted from the discharge flow with Forward Osmosis using the concentrated nutrient solution holds prospects, but extracting irrigation water from brackish groundwater seems less feasible. In a long-term experiment, sodium (Na) standards for sweet pepper have been reinterpreted. It was shown that an increase in the Na standard up to 8-10 mmol/l causes no damage or loss in pepper production. Inaddition, it was shown that the split-root system can be used for uptake of extra Na without growth hampering. Furthermore, applying humate can prevent negative sodium effects at high sodium levels (Chinese cabbage). Finally, insight was gained into the risks associated with the use of chlorinated cleaning products in zero-discharge cultivations.

Het doel van dit project was de realisatie van een proof-of-principle keten voor de productie van astaxanthine als oleoresin uit de alg Haematococcus pluvialis in fotobioreactoren in Nederlandse kassen. Astaxanthine is een sterk antioxidant dat bij kan dragen aan een gezonde voeding voor consumenten. Astaxanthine kan in Nederlandse kassen duurzaam worden geproduceerd (kassen als zonnecollector, gebruik afval CO2 uit industrie, reinigen afvalwater). Binnen dit project is onderzoek verricht naar de selectie van natuurlijke algenstammen op kasniveau, klassieke stamverbetering op labniveau (uitgangsmateriaal), procesverbetering in alle fases van de productie (voorkweek, opkweek, groene fase, rode fase) door optimalisatie teeltfactoren en hygiënisatie (teelt en productie) en het maken van een proof-of-principle eindproduct (eindformulering) volgens marktspecificatie (markt en economie). Met het project is kennis vergaard om een nieuw verdienmodel voor de productie van een hoogwaardige stof (astaxanthine) in de tuinbouw te realiseren. Er is een proof-of-principle van een economisch rendabele productieketen van uitgangsmateriaal over productie tot product eindformulering volgens specificaties van de markt aangetoond voor de productie van astaxanthine uit Haematococcus pluvialis.---The aim of this project was the realization of a proof-of-principle value chain for the production of astaxanthin as oleoresin from the algae Haematococcus pluvialis in photobioreactors in Dutch greenhouses. Astaxanthin is a strong antioxidant that can contribute to a healthy diet for consumers. Astaxanthin can be produced sustainably in Dutch greenhouses (greenhouses as solar collectors, usage of waste CO2 from industry, cleaning and recycling of waste water). Within this project, research was carried out into the selection of natural algae strains at the greenhouse level, classical strain improvement at lab level (starting material), process improvement at all stages of production, from pre-cultivation, cultivation, green phas and red phase, by the optimization of all cultivation factors and sanitation (growth and production) and designing a proof-of-principle end product (formulation) according to market specification (market and economy). With the project, knowledge has been gathered to realize a new revenue model for the production of a high-quality substance (astaxanthin) in horticulture. A proof-of-principle of an economically viable production chain of starting material from production to product final formulation according to market specifications has been demonstrated for the production of astaxanthin from Haematococcus pluvialis.

Application of a mobile unit for discharge water purification is one of four options to apply to the purification obligation per 1-1-2018. Depending on the amount of discharge, future water strategy and investment options, mobile purification can be an interesting option. The amount of discharge water varies with crop, irrigation strategy and quality of the irrigation water and is between 122 and 3.340 m3/ha/year for surveyed companies. About 65% of greenhouse companies discharges