In this context, GROOF "Greenhouse to Reduce CO2 on RooFs", a project led by a number of countries - whose lead partner (CDEC) is from Luxembourg - and supported by the INTERREG programme (NWE), is conducting a study on different off-ground cultivation systems applicable to urban agriculture. It involves players from a wide range of fields (from agronomy to construction), with a view to a circular economy, in order to reduce CO2 emissions and produce as close as possible to consumers. The GROOF concept focuses on the reduction of CO2 emissions by including the recovery of energy lost from urban buildings: plants can thus grow in greenhouses. Above-ground hydroponic and aeroponic cultivation systems guarantee the quality of the products through optimised management of water consumption, energy and the chemical and biological quality of the nutrient solutions.
One of the objectives of this European project is to test and evaluate the different cultivation systems in order to advise the pilots. 2019, which is the first year of the study, will provide comparative results between the different cultivation techniques in order to select the most suitable cultivation system(s) for the four pilots (yield, cost, practicality, environmental impact, etc.).
Coordinated by ASTREDHOR - EST HORTICOLE station, the experiments take place in three locations: EBF in Bensheim (Germany), Les fermes de Gally in Saint-Denis (France) and EST HORTICOLE experimental station in Roville-aux-Chênes (France).
The plants tested are basil, lettuce, chard and pepper. This choice was established according to the demand of the urban market for aromatic herbs, leafy vegetables and fruit vegetables. In addition, these are fast-growing plants with high added value, perfectly adapted to the context of urban rooftop agriculture, which is moreover carried out in greenhouses.
Here are the five cropping systems selected for these experiments, which will be tested from April to August 2019.
Agrilogic Systèmes, based in New Caledonia for 20 years, is an engineering company specialising in the construction of greenhouses and above-ground systems for horticulture. The system allows growers to adapt according to market evolution and demand thanks to the different functionalities of GOPONIC® gutters: bulk substrate, potted substrate, NFT system (Nutrients Film Technics), aeroponics, vertical cultivation. GROOF will experiment its horizontal hydroponic system. These gutters are 6 m long and their secondary level is adjustable according to the plants to be cultivated. The gutters, made of PVC, are very light and rigid and can support up to 60 kg.
This system comes from the Netherlands by the company JB Hydroponics, specialized in horizontal hydroponic systems. Different systems are offered depending on the substrates used for the crops. Bags of peat and coconut can be placed directly on the support gutters installed on the greenhouse slabs, for example.
In our study, 30 litre plastic tubs filled with Biochar charcoal-based substrate are positioned along the entire length of the gutter.
Irrigation is done by drip irrigation above each tray, with water draining out through the interstices underneath the trays. The substrate never remains too wet and collects the drainage water in the gutters to a water reservoir.
This system is simple and very easy to install and can be adjusted according to the plants to be cultivated. The roots can grow easily, the plants are separated by containers, reducing the risk of spreading diseases.
AeroFlo, from GHE, is a substrate-free, hydroponically operated NFT system. Rows of 10 to 120 plants per module can be added without limit. The AeroFlo concept works with a water pump placed in the tank and tubes with nozzles at the ends at different intervals. It offers the advantage of aeroponics by spraying the water inside the gutters on the roots of the plants, on the biodegradable pot installed in the holes provided. Then the water falls back into the gutters to the tank allowing its good oxygenation. This system is very light and easy to install. It requires little maintenance, making production management easier. Other professional urban farmers already use this system such as Les Sourciers, Aeromates or Hydroleb.
Two modules of 40 plants will be tested for the GROOF project. The biodegradable pots will be positioned in the holes.
The Tootem system, created by a Frenchman, is a multicultural solution that is easy to install, scalable and includes sensors, a pump control system and a system for controlling pumps and equipment.
Initially, 95% of the activity of the company offering this system concerns greenhouse lighting (GreenPower LED interlighting system), for strawberry, cucumber and tomato crops. This production innovation was invented 2 years ago and then left aside in the face of the still moderate development of urban agriculture.
This innovation favours the cultivation of all types of plants (leafy plants, fruit plants, aromatic plants, etc.) because it combines vertical and horizontal production systems. Tootem adapts to each crop by offering modules with columns, trellised crops, trays.
Different substrates can be used depending on the crops: clay balls, coconut fibre, coconut bread. This system stands out from the others by the presence of measurement sensors facilitating the piloting of the culture systems (temperature, humidity, light and CO2 sensor). A solar panel connected to the electrical grid makes the system of sensors and pump control autonomous. The data collected will be available on a WEB application and will allow the analysis of parameters such as lighting in order to promote crop densification. Good control of temperatures and O2 levels in the water tends to reduce pathogens and allows for significant savings in water and fertilizer while improving yields.
Tower Garden is an aeroponic turret growing system. Instead of soil, rock wool is used for Tower Garden. This medium creates a moist and well oxygenated environment to facilitate good root development. The plants grow outside the turret and the roots grow inside. A micro-spray of water and nutrients is present in the center of the turret. The water not absorbed by the roots falls back into the collection tank placed under the turrets and is then reintroduced into the system: this is the principle of the closed circuit.
This innovation would ensure a very high yield per m2, freshness and stable production costs all year round. The plants that can be grown on the Tower Farm turrets are: strawberries, cherry tomatoes, small peppers, certain medicinal plants and leafy vegetables (lettuce, lamb's lettuce, arugula, Kale cabbage, young shoots and herbs).
The results of these experiments will be made public by the end of 2019.
With the aim of boosting the concept of rooftop greenhouses, GROOF is launching a call for projects to give successful applicants the chance to benefit from personal coaching from experts according to their one-year project.
Would you like to participate in the project? Don't hesitate any longer and join the GROOF adventure! You have until June 2019 to submit your application. ◉
More information :
Institut Technique de l’Horticulture
Station d’expérimentation Grand EST
28, rue du Chêne
Article published in Neomag #22
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