To investigate the effect of very high hortiscatter (extreme light diffusion) on the growth of a young tomato crop, an experiment was conducted at Wageningen UR Greenhouse Horticulture in Bleiswijk. Three levels of light diffusion were compared: high diffusion (hortiscatter=0.9), medium light diffusion (hortiscatter = 0.65) and direct light or no light diffusion (hortiscatter~0). The plants were placed on elevated growing tables and grown at a high density to simulate the high LAI values of a grown-up crop. The materials allowing for the differences in light diffusion were placed on metal frames above the plants. Each material was used on two tables. D espite a careful set up, the PAR sum was not equal for all tables. This was due to position effects in the greenhouse as well as small differences in light transmission of the covering materials. When both diffusion factor and PAR sum are considered in the analysis of the results of the successive destructive harvests, the plants grown under the high diffusing lamellae showed increased leaf area and higher fresh and dry weight compared to the other two treatments. The light use effi ciency, expressed as grams of dry matter produced per mol PAR, increased with increasing Hortiscatter for the last two destructive harvests. Net photosynthesis increased also with the increase of scattering. A larger trial in separate compartments would be desirable to verify these results in real growing conditions and evaluate the effects on fruit production during a longer experiment.

This report contains an exploration towards additional heat utilization processes that can increase the heat use efficiency of geothermal aquaponics. Each heat use application is selected based on its potential contribution towards circular food production systems. The heat use applications are evaluated based on heat demand and on the extent to which they can be integrated into a geothermal treatment network. This study and the resulting insights into geothermal aquaponic treatment networks have been developed for the EU project GEOFOOD.

Nitrogen supply is a great challenge in organic horticulture. Natural Nitrogen fi xation from ambient air in water through plasma reactors provides an alternative solution for the nitrogen supply in organic farming. Spain has the biggest certifi ed surface of organic cultivation in Europe. Desk and fi eld research by WUR Greenhouse Horticulture & Flower Bulbs in cooperation with VitalFluid, Doornebosch Advies and VanWaarde, within the context of a Top Sector Seed Money Project shows that this innovation would fi t well in the Spanish organic greenhouse sector and could contribute to improve the N-supply and therefore the yields of especially short cycle crops. The province of Almeria concentrates the biggest national share of organic greenhouse horticulture, a good knowledge infrastructure and suitable fi nancial instruments for innovations. Potential users confi rm that Natural Nitrogen will certainly be a solution for the N supply and are willing to adopt it, provided it is successfully demonstrated under local conditions, is price-competitive, approved to be used as input in organic horticulture and it does not negatively affect the soil microbiome or the isotopic footprint of the produce. Certifi cation bodies will approve Natural Nitrogen after it has been included in the EGTOP list of authorized inputs in organic horticulture.

In 2015 Wageningen University & Research, Business Unit Greenhouse Horticulture gathered a group of Dutch supply industry companies around the idea of creating an investment order tool. The companies involved were the fertiliser producer SQM (until 2018), the rockwool producer Grodan, Priva for automation of climate, nutrients and labour, the seed and breeding company Bakker Brothers and the screen producer Ludvig Svensson. Two regions, Jordan and Spain, were chosen to serve as pilot areas for the investment order tool. In Jordan the comparison was between the traditional single tunnel greenhouse and a multi-span greenhouse, in Spain the comparison was between the traditional flat roofed parral greenhouse and a multi-span greenhouse. In both, Jordan and Spain, the improved greenhouse used automation of irrigation, fertilisation, ventilation and screening. In both areas climate measurements were performed. In Almería, the tool was tested in discussions with growers, advisors, researchers, authorities and the Cajamar bank. The tool shows the most profitable order of investment alternatives. The investment tool can help growers to avoid non-profitable investments and to identify choices based on risk aversion. The tool helps supply companies to identify unexpected motivations of growers. The tool helps researchers to focus on some topics around risk control. Finally, the tool helps local authorities to organise effective support actions.

Wageningen University & Research, Business Unit Glastuinbouw heeft samen met PhenoVation en PlantDynamics in opdracht van ‘Kas als Energiebron’ twee methodes om de gewasfotosynthese te monitoren onderzocht: de gewasfotosynthesemonitor en de CropObserver. De data van de gewasfotosynthesemonitor werden vergeleken met de fotosynthesemodule van het gewasgroeimodel INTKAM. Verder werd het dagverloop van de huidmondjesopening bepaald met de Stomatasensor. Uit de metingen bleek dat de gewasfotosynthesemonitor te gevoelig is voor veranderingen in raamstanden en wisselingen in CO2 dosering om de gewasfotosynthese nauwkeurig te kunnen bepalen. De CropObserver bleek een goed beeld te geven van de relatieve lichtbenutting door het gewas. De beste manieren om de gewasfotosynthese nauwkeurig en betrouwbaar te bepalen, zouden de volgende kunnen zijn: 1. Via een fotosynthesemodelmodel (zoals INTKAM) waarmee de gewasfotosynthese berekend kan worden, gekoppeld aan een sensor die de status van het gewas monitort zodat geregistreerd wordt wanneer de reactie van het gewas afwijkt van wat te verwachten zou zijn, of 2. Via de CropObserver, aangevuld met een sensor voor de huidmondjesopening en een meting van tenminste de CO2 concentratie, waarmee het signaal van de CropObserver vertaald kan worden naar CO2 opname door het gewas