QUEL EST LE RÉEL POTENTIEL D'ÉCONOMIE D'EAU D'IRRIGATION A L'ECHELLE DE LA PARCELLE PAR À LA MODERNISATION DES SYSTÈMES D'IRRIGATION ?

As water scarcity intensifies in most countries due to climate change, water savings are of increasing concern and European water-resource policy targets sustainable water management and water savings. For this purpose, farmers' investments in efficient irrigation equipment are supported by the European Agricultural Fund for Rural Development (EAFRD), provided the new irrigation installation can potentially allow water savings of 5 to 25%, without having a negative impact on crop yield. However, no methodology was available so far for the expected ex ante quantification of these water savings.The aims of this study were (1) to gather data of water savings achieved through irrigation system modernization (i.e. change of irrigation system or adoption of irrigation scheduling tools) and to analyze how they are influenced by soil and climate context; (2) to develop a simple tool for the ex-ante assessment of potential water savings, those deemed achievable by changing the irrigation system or adopting scheduling tools (3) to use the Optirrig crop and irrigation model on two case studies to quantify irrigation water losses and irrigation efficiency at the plot level.For this purpose, we compiled available studies conducted over the past 30 years on the French metropolitan territory dealing with documented water savings realized by switching from an irrigation system (hose reel machine, lateral move, center pivot or solid set system) to a more efficient one (center pivot, surface drip, subsurface drip or microsprinkler) or by using soil hydric status probes (tensiometric or capacitive) for irrigation scheduling. Nearly 100 records were collected from experimental field trials representative of a wide range of pedo-climatic conditions and crops (field crops, vegetables, fruits on perennial crops). Each record represents the water consumption of two different irrigation systems or two scheduling systems (without soil probe vs with soil probe) at plot scale and is used to assess the obtained water saving.Results show that (1) the achieved irrigation water savings (when changing irrigation system or adopting soil probes for irrigation scheduling) are highly variable, ranging from 0% to more than 70% and thus are not generalizable; (2) water savings obtained from localized systems significantly decrease when the hydric deficit of the cropping season increases and when soil water holding capacity is high; (3) those obtained from irrigation scheduling using soil probes do not seem to be influenced by the hydric deficit, soil water holding capacity or soil probe type; (4) a referential of potentially achievable water savings through the change of irrigation equipment and/or irrigation management could be established; (5) the use of Optirrig model allowed quantifying water savings originating from the reduction of technical losses (linked with the type of system) and tactical losses (linked with irrigation management and scheduling).