France: Irrigation and fertigation challenges at research center
In Brittany, the 30.000 ha of field-grown vegetables are cultivated in watersheds located near the sea. It is crucial to monitor accurately the fertilisation to avoid nutrient leaching, especially nitrogen. Indeed nutrient leaching leads to a significant development of green algae (ulva) on the seaside, which is an environmental problem. In 1983, CATE set up 17 plots with lysimetric equipments to measure risks of nitrogen leaching in local conditions (loamy-sandy soil, 900mm of annual rainfall), to carry out long-term experimentation in collaboration with INRA and the chamber of Agriculture. During the past 30 years, trials have been carried out to assess the natural mineralisation from the soil and the impact of different fertilisation practices on nutrient leaching. Suction cup devices collect the leachate at different depths and enable to follow precisely the nitrogen kinetic through the soil, and the drainage is collected.
The range of vegetables, traditionally grown in the region (cauliflower, “camus“ artichoke), was well-adapted to the local climate and does not require irrigation. But the recent diversification led growers to grow short-cycle crops: broccoli, lettuce, “purple” artichoke, etc., which enhance the development of irrigation in the region. But fertigation is not yet implemented because its use would not be cost-effective.
CATE is also working on integrated pest management to reduce the inputs in the cropping systems, in the framework of a French program named Ecophyto which aims to reduce the use of pesticides by 2025 with 50%.
In the Brittanian greenhouses mainly soilless tomatoes and strawberries are cultivated. In the greenhouses, fertigation is used and the predominant source of irrigation is rainwater. Rainwater has replaced the use of groundwater, which helps to overcome the problems occurred by the high sodium levels in the underground water due to the proximity of the sea. The underground water has sodium levels as high as 70mg/L. The drainage from the tomato and strawberry soilless production is collected, treated by slow sand filtration (biofiltration) and then recirculated. Trials about water treatments and drainage recirculation have been carried out at CATE for the last 20 years. Currently, a new greenhouse is being built at CATE. Here an alternative water disinfection treatment will be installed, the middle-pressure UV disinfection system. From 2017, the new greenhouse will enable to test different climate monitoring and crop management practices on tomato.