Hysterisis of soil hydraulic properties and critical irrigation thresholds of crops

水对农作物至关重要，但在世界各地都面临着稀缺。农业必须提高生产力，以满足未来几年日益增长的粮食需求，而灌溉是实现这些增长的关键组成部分。然而，灌溉需求的预测增长和合格人力的缺乏将需要建立更多的智能，以帮助灌溉决策，以节约用水和提高作物产量。 灌溉管理中的主流方法仍然主要基于计算蒸散需求。然而，最近的工作表明，通过采用真实的评估从土壤到植物根系的水分转移的方法（产量增加20-50%，节水高达65%），并使用临界基质势阈值来启动作物灌溉，可以取得显著的收益。 临界灌溉阈值是那些土壤基质势（土壤吸力），确保最低所需的适当转移的水从土壤中的植物在真实的时间。这是灌溉管理智能化的一个关键参数。为了估计这些阈值，必须在现场表征土壤水力特性。然而，这些特性是滞后的，根据土壤是否被润湿或干燥而不同。部分由于滞后现象，有必要通过许多现场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关键阈值所需的情报。它将集中在非饱和水力传导率函数的滞后，评估其在推导临界灌溉阈值的作用。 该计划的第一年（步骤S.1）将致力于构建仪器化容器和土壤表征（S.2），随后（S.3，第2年和第3年）用于在3种土壤类型（沙子，壤土，粘土）上种植两种作物，在测试阶段，将定期测量土壤和植物参数。在S.4中，将使用收集的实验数据的不同分析和数值方法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）来评估滞后对土壤供水的影响，并确定必要的测量范围，以充分量化临界灌溉阈值确定的非饱和导水率。在最后一步（S.6）中，将对不同土壤和作物的临界阈值进行独立验证。 从长远来看，开发一种用于确定临界阈值的自动化实时方法将是世界性的突破，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.