Study On Monitoring And Estimation Methods Of Stomatal Resistance And Canopy Resistance Of Winter Wheat And Summer Maize

Stomatal resistance and canopy resistance are important parameters of crop evapotranspiration study. They are different and related. Stomatal resistance is the resistance of water vapor in and out of plant stomata, which is the basis for the evapotranspiration on the plant scale. Canopy resistance is the basic parameter of evaporation and transpiration on the field scale, the basic starting point is generalized crop canopy into a "big leaf".According to the "big leaf theory" canopy resistance is the integrated of leaf stomatal resistance and soil resistance. Whether there is the same variation between stomatal resistance and canopy resistance, or through the establishment of the relationship between them to do conversion between different scales is a widespread concern topic at home and abroad. In this thesis, based on the large number of field measured data, we analyzed the changing process of stomatal resistance of winter wheat and summer maize growth on days and growth season, studied the effects of environmental factors on stomatal resistance, and compared the method of using Penman-Monteith equation inversed crop canopy resistance and using stomatal resistance calculated canopy resistance, the main results as follows:1.The diurnal variations of stomatal resistance of different crops are various. Diurnal variation of stomatal resistance of winter wheat is on the performance of "W-type". Stomatal resistance is higher in the early, middle and late time in daytime, the peak would be less or disappearance and likes as the "U-type"if the supply of soil moisture is adequate, or the temperature is low on the early growth stage. The diurnal variations of stomatal resistance of summer maize like as "U-type" in all measurement days with the higher values in the morning and evening time.2.Stomatal resistance of winter wheat change as multiple peaks curve throughout the growth period. It is higher (to start after turning green period) at the early growth stage then tune to less with plant vigorous growth, and a resistance increase point often is seen on heading and filling stage, then decreases again, stomatal resistance increases gradually with the crop aging and declining of leaf functional. On the whole the stomatal resistance of winter wheat in the whole growth season shows as a multiple peaks curve. While the stomatal resistance of summer maize are basically gentle rise in the whole growth period.3.Factors determine stomatal resistances on different crops are not the same. The most important factors affecting stomatal resistance on winter wheat are in the order of relative humidity, temperature, transpiration and canopy-air temperature difference.The most important environmental factors on summer maize are net radiation, temperature and relative humidity.4.Canopy resistance can be calculated in different ways, but different methods for different crops are in different degree of agreement. Using stomatal resistance combined of leaf area index to calculated canopy resistance has the same trends in the days with the measured stomatal resistance, but the value is less.Calculated canopy resistance in plant and cell scale in this method is more accurate. The diurnal variation of canopy resistance shows a simple trend by using PM formula promoted on the medium scale.Canopy stomatal resistance values calculated with the two methods are larger different. Correlation of summer maize canopy resistance calculated by those two methods is good, both are in good agreement in numerical size and trends.