Hysterisis of soil hydraulic properties and critical irrigation thresholds of crops

水对农作物至关重要，全球范围内都面临着缺水的问题。农业必须提高生产力，以满足未来几年不断增长的粮食需求，而灌溉是实现这些增长的关键组成部分。然而，预计灌溉需求的增长和合格人力的缺乏将需要建立更多的智能来协助灌溉决策，以节约用水和提高作物生产力。******灌溉管理的普遍方法仍然主要基于计算蒸散需求。然而，最近的工作表明，通过使用包括实时评估从土壤到植物根系的水分转移（产量增加20-50%，节水高达65%）和使用关键基质潜在阈值来启动作物灌溉的方法，可以实现显著的收益。******关键灌溉阈值是指那些土壤基质电位（土壤吸力），它确保了从土壤到植物的实时适当的水转移的最低要求。这是灌溉管理智能化的关键参数。为了估计这些阈值，必须在现场对土壤的水力特性进行表征。然而，这些特性是滞后的，根据土壤是湿润还是干燥而有所不同。由于迟滞现象的部分原因，有必要通过许多实地实验来经验性地估计临界阈值，这需要大量的努力、时间和资源。******拟议的计划旨在建立更好地估计这些临界阈值所需的情报。它将侧重于不饱和水力传导功能的滞后，评估其在导出关键灌溉阈值中的作用。******该计划的第一年（步骤S.1）将致力于仪表容器的构建和土壤表征（S.2），后来用于（S.3，第2和第3年）在3种土壤类型（砂，壤土，粘土）上种植两种作物，在测试阶段，土壤和植物参数将定期测量。在S.4中，使用收集的实验数据的不同分析和数值方法将与估计的临界阈值进行比较。然后将使用最准确的方法（S.5）来评估迟滞对土壤供水的影响，并确定为确定关键灌溉阈值而充分量化非饱和水力导电性所需的测量范围。在最后一步（S.6）中，将对不同土壤和作物的导出临界阈值进行独立验证。******从长远来看，开发一种自动化的实时方法来确定临界阈值将是一个世界性的突破，成为改善灌溉性能和作物生产力的快速通道，以更好地利用水和农业投入资源。**

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. **