The study proposed a new crop water stress indicator - the mean value of Gaussian distribution of excess green index for maize canopy (MGDEXG) within an RGB image. A series of RGB images were collected in a maize field under varying levels of deficit irrigation during 2013, 2015 and 2016 growth seasons in northern Colorado. To evaluate the sensitivity of MGDEXG to maize water status, canopy temperature, canopy-to-air temperature difference, crop water stress index (CWSI), leaf water potential, and sap flow were used as water status references. The results show that MGDEXG distinguished different levels of deficit irrigation treatments well and responded to the release and reimposition of deficit irrigation. The MGDEXG showed a significant correlation (p < 0.01) to different water stress references. Especially, the coefficient of determination (R²) with CWSI was 0.63 (n = 59) for 2013, 0.80 (n = 90) for 2015, and 0.80 (n = 50) for 2016. In addition, among the three Tc-based water stress indicators, the relationship between MGDEXG and CWSI was the most robust with the least annual changes of slope and intercept. The robust relationship between MGDEXG and CWSI could also show that MGDEXG was resistant to the micro-meteorological conditions within the field. Significant correlations (p < 0.01) were found between MGDEXG and leaf water potential with R² of 0.85 and 0.87 for 2013 and 2015, and between MGDEXG and sap flow in 2015 (R² = 0.62). MGDEXG relies only on the distribution of crop pixels within an RGB image and could be calculated easily, so it could be cheaper or easier to popularize than other crop water stress indicators in practice. Overall, our results show that MGDEXG could be successfully used as a maize water stress indicator. In the future, more field experiments are needed to further explore the changes of MGDEXG with different scale and spatial resolution of RGB images, and to evaluate MGDEXG for specific climate and crop varieties.

该研究提出了一种新的作物水分胁迫指标-RGB图像内玉米冠层（MGDEXG）多余绿色指数的高斯分布平均值。在2013年，2015年和2016年北科罗拉多州的生长季中，在不同水平的亏缺灌溉条件下，在玉米田中收集了一系列RGB图像。为了评估MGDEXG对玉米水分状况的敏感性，将冠层温度，冠层与空气之间的温差，作物水分胁迫指数（CWSI），叶水势和汁液流量用作水分状况参考。结果表明，MGDEG很好地区分了不同水平的亏水灌溉处理方式，并对亏缺灌溉的释放和再利用做出了响应。MGDEXG与不同的水分胁迫参考值显示出显着的相关性（p <0.01）。特别是，确定系数（R²）的CWSI为2013年的0.63（n = 59），2015年的0.80（n = 90）和2016年的0.80（n = 50）。此外，在三个基于Tc的水分胁迫指标中，MGDEXG之间的关系CWSI最强大，且斜率和截距的年度变化最少。MGDEXG和CWSI之间的牢固关系也可能表明MGDEXG对田间的微气象条件具有抵抗力。发现MGDEXG与叶片水势之间存在显着相关性（p <0.01），2013和2015年R ^2分别为0.85和0.87,2015年MGDEXG与汁液流量之间（R ²= 0.62）。MGDEXG仅依赖于RGB图像内作物像素的分布，并且易于计算，因此与实际中的其他作物水分胁迫指标相比，它更便宜或更易于推广。总体而言，我们的结果表明MGDEXG可以成功用作玉米水分胁迫指标。将来，还需要进行更多的田间试验，以进一步探索MGDEXG在RGB图像的不同比例和空间分辨率下的变化，并针对特定的气候和农作物品种评估MGDEXG。