In semi-arid and arid regions, crops face elevated atmospheric demands and endure prolonged periods of moderate to severe water scarcity. In this context, this study investigated the effectiveness of the photochemical reflectance index (PRI) and a normalized surface temperature index (Tnorm) for proxy detection of the water stress of winter wheat crops. Furthermore, the potential of PRI for characterizing water, atmospheric or photo-inhibition stress, and wheat transpiration was assessed over experimental drip-irrigated crop fields in the Haouz plain, central Morocco. In practice, PRI observations were compared to agro-environmental variables such as Leaf Area Index (LAI), Available Water Content (AWC) at a root zone depth, net Radiation (Rn), Vapor Pressure Deficit (VPD) and the wheat transpiration derived from sap flows, lysimeters and a crop water balance model. Due to the strong relationship between PRI and LAI (R2 = 0.91), another index named PRIj was derived to correct for this effect. The PRIj was found to be independent of structural effects related to LAI and significantly correlated with AWC (R2 = 0.85). Using the PRIj index, we can reflect the level of water stress experienced by the wheat field throughout the experiment with an R2 of 0.69 for a FAO-56 water stress coefficient (Ks) of less than 1. Under dry conditions, for an AWC below 30%, the correlation between AWC and Tnorm gives an R2 of 0.29. However, comparison of PRIj with the Tnorm index showed that PRIj is an early water stress index and provides information on the state of the vegetation cover at all stages of wheat development. The study's findings can have a significant impact on the use of the PRI as a water stress indicator, helping in the optimal irrigation of crops.

中文翻译：

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基于光化学反射指数和地表温度数据对小麦水分胁迫的代理检测


在半干旱和干旱地区，农作物面临更高的大气需求，并长期遭受中度至重度缺水。在此背景下，本研究调查了光化学反射指数 （PRI） 和归一化表面温度指数 （Tnorm） 对冬小麦作物水分胁迫代理检测的有效性。此外，在摩洛哥中部 Haouz 平原的实验滴灌农田上评估了 PRI 表征水、大气或光抑制胁迫以及小麦蒸腾的潜力。在实践中，将 PRI 观察结果与农业环境变量进行比较，例如叶面积指数 （LAI）、根区深度的可用含水量 （AWC）、净辐射 （Rn）、蒸气压差 （VPD） 和来自树液流的小麦蒸腾、溶度计和作物水分平衡模型。由于 PRI 和 LAI 之间的强关系 （R2 = 0.91），因此推导出了另一个名为 PRIj 的指数来校正这种影响。发现 PRIj 独立于与 LAI 相关的结构效应，并且与 AWC 显著相关 （R2 = 0.85）。使用 PRIj 指数，我们可以反映麦田在整个试验过程中经历的水分胁迫水平，当 FAO-56 水分胁迫系数 （Ks） 小于 1 时，R2 为 0.69。在干燥条件下，对于低于 30% 的 AWC，AWC 和 Tnorm 之间的相关性得出 R2 为 0.29。然而，PRIj 与 Tnorm 指数的比较表明，PRIj 是一种早期水分胁迫指数，可提供有关小麦发育各个阶段植被覆盖状况的信息。该研究的结果可以对使用 PRI 作为水分压力指标产生重大影响，有助于作物的最佳灌溉。