Water scarcity is one of the major factors limiting crop growth and productivity. Judicious water management reduces the application of irrigation water and increases grain yield, farm profits, and water use efficiency. The assessment of crop water status is the key to in-season irrigation scheduling. The plant diagnostic approach has the potential to assess the in-season crop water status for optimizing crop water use. For this purpose, a series of field and rainout shelter experiments with varying amounts of irrigation water (0–275 mm for field and 0–315 mm for rainout shelter experiments) and planting densities (6–8 ×10⁴ plants ha⁻¹) using seven maize cultivars were conducted from the 2017–2020 growing seasons in North China Plain to determine and validate the plant critical saturated water accumulation (SWA) curve during the vegetative growth period of maize. The result showed that the plant dry mass (DM) and the SWA ranged from 0.07 to 8.22 t ha⁻¹ and 0.63–59.06 t ha⁻¹ during the vegetative growth period of maize, respectively. The plant DM and SWA increased with the increase in irrigation amount. However, plant DM and plant SWA showed non-significant differences under non-water-limiting conditions. An allometric relationship between plant DM and plant SWA was used to develop the plant critical SWA curve (SWA = 8.26DM^0.89, R² =0.98^**). A plant water diagnosis index (WDI) was then derived using the critical SWA curve to quantitatively assess the in-season water status of maize. The WDI increased with the increase of irrigation amount and ranged from 0.72 to 1.26 with a value of 1, indicating an optimum plant water status. The newly developed curve could diagnose and categorize the water-limiting and non-water-limiting plant water status and can be employed for precision irrigation management during maize cultivation.

缺水是限制作物生长和生产力的主要因素之一。明智的水资源管理可以减少灌溉用水，提高粮食产量、农场利润和用水效率。作物水分状况的评估是当季灌溉调度的关键。植物诊断方法具有评估当季作物水分状况以优化作物水分利用的潜力。为此，进行了一系列田间和雨棚实验，灌溉水量（田间 0-275 毫米，雨棚实验 0-315 毫米）和种植密度（6-8 ×10 ⁴株公顷^-1) 利用华北平原 2017-2020 年生长期的 7 个玉米品种，确定并验证了玉米营养生长期植物临界饱和水蓄积 (SWA) 曲线。结果表明，玉米营养生长期的植物干重（DM）和SWA分别为0.07~8.22 t ha ^-1和0.63~59.06 t ha ^{-1 。}植物 DM 和 SWA 随灌水量的增加而增加。然而，植物 DM 和植物 SWA 在非限水条件下表现出非显着差异。植物 DM 和植物 SWA 之间的异速生长关系用于开发植物临界 SWA 曲线 (SWA = 8.26DM ^0.89 , R ² =0.98 ^**）。然后使用临界 SWA 曲线导出植物水分诊断指数 (WDI)，以定量评估玉米的季节水分状况。WDI随着灌溉量的增加而增加，范围为0.72～1.26，值为1，表明植物处于最佳水分状态。新开发的曲线可以对限制水和非限制水的植物水分状况进行诊断和分类，可用于玉米种植过程中的精准灌溉管理。