Hysterisis of soil hydraulic properties and critical irrigation thresholds of crops

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Water is crucial to crops and is facing rarefication across the world. Agriculture must improve its productivity to meet increasing demands for food in the coming years and irrigation is a key component for achieving these increases. However, the predicted growth in irrigation needs and the coming lack of qualified manpower will require more intelligence to be built to assist decision making in irrigation to conserve water and improve crop productivity. ******Prevailing approaches in irrigation management remain based largely on calculating evapotranspiration demand. However, recent work have shown that significant gain may be achieved by using approaches that incorporate an assessment of water transfers from soil to plant roots in real time (yield gains of 20-50% and water savings up to 65%) and use critical matric potential thresholds to initiate irrigation of crops. ******Critical irrigation thresholds are those soil matric potentials (soil suction) that ensure the minimum required appropriate transfers of water from the soil to the plant in real time. This is a key parameter to intelligence in irrigation management. To estimate these thresholds, soil hydraulic properties must be characterized on site. However, such properties are hysteretic, differing according to whether the soil is being wetted or dried. Due in part to hysteretic phenomena, it is necessary to estimate critical thresholds empirically through many field experiments, requiring significant efforts, time and resources. ******The proposed program aims at building the intelligence needed to better estimate these critical thresholds. It will focus on the hysteresis of the unsaturated hydraulic conductivity function, assessing its role in deriving critical irrigation thresholds. ******Year 1 of the program (Step S.1) will be devoted to the construction of instrumented containers and soil characterization (S.2), later used (S.3, year 2 and 3) for growing two crops on 3 soil types (sand, loam, clay), in a testing phase during which soil and plant parameters will be measured regularly. In S.4, different analytical and numerical approaches using the collected experimental data will be compared to estimated critical thresholds. The most accurate approaches will then be used (S.5) to evaluate the effect of hysteresis on soil water supply and to determine the range of measurements needed to quantify adequately the unsaturated hydraulic conductivity for critical irrigation threshold determination. In the last step (S.6), independent verifications of the derived critical thresholds for different soils and crops will be performed.******In the long term, the development of an automated real-time method for determination of critical thresholds will be a world breakthrough, becoming a fast track for improving irrigation performances and crop productivity for a better use of water and agricultural input resources. **