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L'Unité Expérimentale de Gotheron développe des programmes d'expérimentation-recherche sur les systèmes de production durable en  ARBORICULTURE  fruitière (abricotiers, pêchers, pommiers, poiriers). © MAITRE Christophe

Water and agriculture

Nitrates and pesticides in water

INRA researchers have developed models to examine how two major agricultural pollutants, nitrates and pesticides, are transferred to water. TNT2, the model developed by researchers in Rennes, makes it possible to assess how nitrogen enters and exits a catchment basin depending on different agricultural practices.

From the moment water enters a catchment basin to its exit through an outlet, it follows different paths. It becomes runoff, is absorbed by the soil, becomes groundwater, or overflows and feeds rivers. As it does so, it changes chemical composition and transports pollutants in dissolved or particulate form (e.g. nitrates, phosphorus, pesticides, heavy metals and micropollutants). INRA studies the main agricultural pollutants: nitrates and plant protection products with very different modes of circulation. Nitrates are very soluble in water, but spread slowly and most are absorbed by groundwater. Pesticides are generally carried away by surface runoff. INRA researchers have developed models to study how these pollutants are transferred to water.

Excess nitrates are difficult to reabsorb

TNT2, the model developed by researchers in Rennes, makes it possible to assess how nitrogen enters and exits a catchment basin depending on different agricultural practices. Built using real measurements, it is able to quantify nitrogen flows (including volatilization and mineralization) using parameters unique to each basin: the climate, soil type, hydrographic network, etc. The model demonstrates that a strategy reducing nitrate fertilisers has limits and must be accompanied by a major change in crop systems. Designing new systems with low levels of nitrogen loss is one of the new challenges facing agronomic research.

“Those managing water resources used the results of our model to develop the national plan to fight green algae,” says Patrick Durand, director of the SAS research unit in Rennes. “Things are beginning to get better in Brittany, but nitrate rates are still increasing in other regions, like the Parisian basin and the Pays de Loire region, where longer transfer times have led to less awareness of the issue.”

 

Attacking pesticides

Researchers from the LISAH research unit in Montpellier studied pesticide transfer in wine-growing areas. They developed a model based on the same principles as the nitrate model. The Mydhas model has several functions, including predicting water contamination risks for different crop practices. Researchers recently made a significant breakthrough by proving that the soil/water partition coefficient of pesticides changes over time. “This coefficient is decisive because it allows us to determine what proportion of pesticides dissolves in water and what proportion attaches to soil particles. Manufacturers identify a fixed parameter for each product in laboratory conditions. But in real conditions, it varies depending on soil wetting-drying cycles as determined by the climate. A better estimate of this parameter, obtained by combining laboratory experiments and observing pesticide flows in plots over several years, has allowed us to considerably improve the model’s predictive ability,” says Jérôme Molénat, director of the LISAH research unit. The model will be used to develop a decision-making tool as part of a partnership with private companies. Designed for agricultural and environmental engineering companies and territorial managers (state authorities or technical departments in territorial authorities), this tool will help define new, less polluting, practices. The initiative was awarded the “Hydro-innovation 2011” prize at the Hydrogaïa international water exhibition for water professionals.

Landscape advantages

INRA researchers also study buffer elements in landscapes:

- Wetlands, which capture some nitrates, retain trace metal elements and break down pesticides.

- Drains, which modify pesticide flows by restricting runoff and encouraging infiltration in groundwater.

- Grassed buffer strips, which reduce the amount of pesticides reaching watercourses.