Diagnosing crop water status based on canopy temperature as a function of film mulching and deficit irrigation

Film mulching with deficit irrigation is considered an effective way to maximize water productivity and ensure a stable crop yield in the arid region of Northwest China. Deficit irrigation requires precise knowledge of crop response to drought conditions, whereas the canopy temperature and the related crop water stress index (CWSI) monitor crop water stress status. Although canopy temperature and CWSI are closely related to meteorological conditions, cultivation measure and crop growing conditions, it is unclear how film mulching influences the canopy temperature and CWSI. A two-year field experiment was conducted in a maize field with three irrigation levels and different film mulching conditions, i.e., non-mulching, plastic film mulching and biodegradable film mulching treatments, in the Shiyang River Basin of Northwest China. The study aimed to quantify the effects of film mulching on canopy temperature and CWSI, as well as to compare CWSI values obtained from the nearby meteorological station data (CWSI_M), and in situ (field) measurements (CWSI_I). The results showed that plastic film and biodegradable film significantly (p < 0.05) reduced the canopy temperature. The non-water-stressed baseline based on the air temperature and relative humidity of the nearby meteorological station was significantly (p < 0.05) different from those of the field measurement at both the vegetative and the reproductive stages. No significant differences in the non-water-stressed baselines (p > 0.05) were observed among different film mulching conditions. CWSI was calculated using the air temperature and relative humidity data from the aforementioned two sources. The results revealed showing that CWSI_I better correlated with the crop yields of various treatments when compared to CWSI_M. Irrigation scheduling based on CWSI_I could save 83 mm of irrigation amount. This underscore the preference of using CWSI_I (if available) as the primary choice for irrigation scheduling. These findings highlight the impact of meteorological and planting conditions on the canopy temperature, non-water-stressed baseline and CWSI, which may be valuable for diagnosing crop water status more accurately by regional water managers.