France: Growing tomatoes with rainwater
In 2014, at the time of the last enlargement, SARL du Hun was extended with a new water reservoir. This resulted in a rainwater storage capacity of 50.000 m3. The rainwater storage increased the resilience of the crops as rainwater harvesting ensures an autonomous reliable water resource of good quality and avoids problems that occurred in the past when using groundwater which had poorer quality (high levels of iron and sodium). Moreover, SARL du Hun doesn’t need to demonstrate compliance with the legislation associated with groundwater use. Recently, they installed floating pumps to abstract water from the reservoir because sediments accumulation at the bottom of the reservoir clogged the pumps.
The water from the reservoir is transferred to the main fertilisation unit where the stock is prepared at E.C. 4 dS m-1. The fertigation solution will be further diluted in each sub-fertilisation station (4 in total) found at each greenhouse to achieve the targeted E.C. The sub-units are used to decrease the storage capacity needed for the nutrient solution and to maximise the potential of the fertilisation unit. At Sarl du Hun the excess of irrigation water, further referred to as drainage water, is recirculated. This means that the drainage water is mixed with fresh rainwater and nutrients. To adjust the nutrient solution after mixing both drainage water and rain water, the drainage is analysed every 3-4 weeks. Irrigation is managed automatically; the first event of the day is fixed scheduled on a timer and thereafter the irrigation is triggered by a solar meter when the targeted light values are reached. At SARL du Hun, they as well monitor substrate (rock wool) moisture content by a moisture meter.
From the beginning of the growing season, all the drainage is recycled after being disinfected using chlorine dioxide. The disinfection method has been selected for the ease of implementation (minor investment cost compared to UV or slow sand filtration) but they are not satisfied with it as it isn’t really efficient and requires too much monitoring. The biofilm in irrigation pipes is a real problem. Occasionally problems with Agrobacterium rhizogenes (crazy roots) appear. The growers believe that this is due to the insufficiency of the system. There is a need to improve the disinfection and the growers are looking for alternative disinfection systems. They would like to install a new disinfection system but the high investment costs for UV or biofiltration is the main limitation for their implementation.
Source: FERTINNOWA