Mornitoring The Water Status On The Temperater Of Palant And Atmosphere In Wheat

Real-time monitoring and rapid diagnostics of crop water status based on canopy temperature is of significant importance for promoting precise irrigation techniques and improving the efficiency of agricultural water use. This study was based on experiments using wheat plants under different water and nitrogen treatments in different years. The aims were to clarify temporal and spatial variation in the wheat canopy and in leaf temperature and moisture, analyze the quantitative relationship between the temperature index and moisture index under different methods of observation, and develop a moisture-monitoring model based on stable and sensitive temperature indicators. These results provide a theoretical basis and key technologies for the accurate diagnosis of wheat moisture and the development of automatic irrigation technology for farmland.First, we studied the dynamic changes in wheat canopy temperature and moisture index, and analyzed the quantitative relationship between the top leaf temperature and the leaf-air temperature difference using leaf photosynthetic indicators. The results showed that the wheat canopy temperature and canopy-air temperature difference decreased as soil moisture increased; that canopy temperature and the canopy-air temperature difference decreased in daytime after sunrise; and that the canopy-air temperature difference varied with advanced growth and as the differences between treatments became increasingly significant. The top leaf net photosynthetic rate (Pn) decreased with advancing growth stage. Stomatal conductance (Cond) first decreased with advancing growth and flowering and then increased before declining again. Transpiration rate (Tr) fluctuated with growth progression, and differences between the photosynthetic indices grew gradually larger. Soil moisture content increased as the plant and leaf layer water content increased in the wheat, but decreased in later growth stages as the difference between treatments became more significant. The Significant correlations of top leaf temperature and leaf-air temperature difference with Pn, Cond, and Tr were found (P<0.05). The strong correlation observed between leaf-air temperature difference and transpiration rate was used for modeling the growth period, with a model coefficient (R2) of 0.60. Independent data were used to test the model’s prediction accuracy (R), which was 0.82, predicting a relative root mean square error (RRMSE) of 29.48%.We then analyzed the variation in canopy temperature at different heights and the relationship between crop canopy temperature at different heights and crop water status. The results showed that plant canopy temperature at different heights displayed significant spatial and temporal variation. Before flowering, canopy temperature decreased gradually and regularly with increasing height. As the growth stage progressed past the flowering stage, canopy temperature first decreased and then increased in a regular pattern. The relationship between the crop moisture index and canopy-air temperature difference in all growth stages after flowering (including flowering), obtained by observations taken at the side of the canopy, was strong, with coefficients of determination as high as 0.54. At all canopy heights, the canopy-air temperature difference in the upper canopy was well correlated with the crop moisture index, with correlation coefficients as high as -0.73. The canopy-air temperature difference measured using side observation was not as good at predicting the effects of water status as was the canopy-air temperature difference observed using above canopy measurements.Finally, we examined the variation in canopy temperature indicators measured at different angles to clarify the quantitative relationship between crop moisture conditions and the canopy-air temperature difference under different viewing angles. We analyzed the relationship between the crop water stress index (CWSI) and plant water status based on the canopy-air temperature difference using the air temperature and humidity monitoring CWSI model. The results showed that, in addition to the jointing and booting stages, the canopy-air temperature differences increased with reduced soil moisture. Two observation angles,0° and -30°, obtained measurements showing that the plant canopy-air temperature difference was well correlated with both plant water content and leaf layer water content. The correlation between canopy temperature measured at 0° and -30° in the filling stage and crop moisture indicators was relatively strong compared with that for other growth stages, providing coefficients of determination (R2) of 0.56 and 0.60, respectively. Overall, the -30° zenith used for observing the canopy-air temperature difference was better at indicating the water conditions of winter wheat than were measurements taken at 0°. The correlation between CWSI and crop moisture indicators was significant, and the coefficient of determination (R2) of the relationship exceeded 0.48. By analyzing the relationship between canopy-air temperature difference and CWSI, and by considering the effect of environmental humidity, a simpler and more stable CWSI empirical formula was obtained. The CWSI monitoring model based on a canopy-air temperature difference observed at the 0° zenith angle was CWSI=0.198+0.051* DTc-a+0.011* VPD, R2= 0.782, and the model based on the canopy-air temperature difference observed at the -30° zenith angle was CWSI=0.225+0.052* DTc-a+0.011* VPD, R2=0.768.