Estimation of Crop Water Stress in Cotton Fields and in Vineyards by Thermal Imagery for Site-specific Irrigation

摘要

Canopy temperature has been recognized for a long time as an indicator of plant water status and as a potential tool for irrigation scheduling. In the present study we investigated the potential of using thermal-images for in-field estimation of the water status of cotton and vineyards under a range of irrigation regimes. Thermal images were taken with a radiometric infrared video camera. Specific leaves that appeared in the camera field of view were sampled, their leaf water potential (LWP) was measured and their temperature was calculated from the images. In grapevines, the stem water potential (SWP) was also measured. Regression models were built in order to predict LWP/SWP according to the crop canopy temperature and to the empirical formulation of crop water stress index (CWSI).rnIn cotton: Statistical analysis revealed that the relationship between CWSI and LWP was more stable than that between canopy temperature and LWP. The regression models of LWP against CWSI and against leaf temperatures were used to create LWP maps. The distribution of LWP in the maps showed that irrigation treatments were well distinguished from each other. Furthermore, the inclusion of the spatial pattern in the classification enhanced the differences between the treatments and was better matched to irrigation amounts.rnIn vineyards: Colour images were fused with thermal images to enable the separation between soil and canopy and between sunlit and shaded leaves. Temperature of different canopy segments was extracted by combining thermal with color images. Crop water index was calculated using both empirical and the theoretical index formulations. The effect of temperatures measured from different parts of the canopy on the prediction of crop water stress index is presented, both for empirical and the theoretical index formulations.