Abstract The accurate estimation of plant water needs is the first step for achieving high crop water productivity. The main objective of the work was to develop an irrigation scheduling procedure for mandarin orchards under Mediterranean conditions based on replacing the amount of consumed water using reference values of soil moisture according to different phenological periods. The proposed methodology includes a definition part where the threshold values were established relating the trees’ stem water potential and the volumetric soil water content measured with Frequency Domain Reflectometry probes. A second part includes the steps for standardizing measurements from capacitance probes by using the LEACHM hydrological simulation model to take into account the sensor-to-sensor variations. Finally, an extrapolation procedure based on soil water retention curves was used for adapting critical soil water content thresholds to different soil conditions. Field evaluations were made in a citrus orchard located in eastern Spain during two seasons. Standardize critical soil water contents were: i) 24 % vol. for post-harvest, bloom - fruit set and phase III of fruit growth; ii) 27 % vol. for phase I of fruit growth, and iii) 29 % vol. for phase II of fruit growth with average daily air vapour pressure deficit values ranging between 0.2 - 0.4; 0.9–1.1 and 1.1–1.3 kPa, respectively. When implemented in the orchard, the sensor-based strategy resulted in water saving of 26 % respect to a control treatment, irrigated using the standard FAO-56 approach, without significant differences in yield and increasing the crop water productivity by 33 %. In conclusion, we suggest that the determination and use of the critical soil water content is a useful tool for scheduling irrigation. The proposed standardization and extrapolation methodology allows the irrigation strategy to be applied to other mandarin orchards under similar climatic conditions.

中文翻译：

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基于频域反射法土壤水分监测的柑桔灌溉调度

摘要 准确估计植物需水量是实现高作物水分生产力的第一步。这项工作的主要目标是开发地中海条件下柑橘园的灌溉调度程序，该程序基于根据不同物候时期使用土壤水分参考值来替换消耗的水量。所提出的方法包括定义部分，在该部分中建立了阈值，这些阈值与树木的茎水势和使用频域反射计探头测量的土壤体积含水量相关。第二部分包括通过使用 LEACHM 水文模拟模型将电容探头的测量值标准化以将传感器到传感器的变化考虑在内的步骤。最后，基于土壤保水曲线的外推程序用于使临界土壤含水量阈值适应不同的土壤条件。在两个季节期间，在位于西班牙东部的柑橘园进行了实地评估。标准化临界土壤含水量是：i) 24% vol。用于收获后、开花-坐果和果实生长的第三阶段；ii) 27% 体积。用于水果生长的第一阶段，以及 iii) 29 % vol。对于水果生长的第二阶段，平均每日空气蒸汽压差值在 0.2 - 0.4 之间；分别为 0.9–1.1 和 1.1–1.3 kPa。在果园中实施时，基于传感器的策略与对照处理相比，节水 26%，使用标准的 FAO-56 方法灌溉，产量没有显着差异，作物用水生产率提高了 33%。总之，我们建议确定和使用临界土壤含水量是安排灌溉的有用工具。拟议的标准化和外推方法允许将灌溉策略应用于类似气候条件下的其他柑橘园。