Measurement Of Crop Evapotranspiration Via Lysimeters With Different Diameters And Simulation Of Canopy Resistance

Evapotranspiration was an important component of the surface water cycle, also an important and complex physical process in the soil-vegetation-atmosphere system.Measuring evapotranspiration by weighing lysimeters was recognized as a standard method. Large scale weighing lysimeters was of high weight, high cost, complex installation, maintenance and management, difficult to repeat the experiment of different treatments, not suitable for large-scale application. Small scale lysimeters could solve the problem, but there was no unified conclusion now for the applicability of the small scale lysimeters.In terms of actual evapotranspiration simulation, although Penman-Monteith model could estimate the ground surface evaporation accurately and widely used, the key parameters affected the accuracy of the model, canopy resistance, γc, was difficult to determine accurately, which restricted the Penman-Monteith model in practical application.This article researched on mainly two aspects, comparison of measured evapotranspiration (winter wheat, rice) by different scale (1 m2,2 m2,4 m2) lysimeters and construction of the canopy resistance model, drawing the following conclusions:(1) Daily variation and trends of evapotranspiration measured by 2 m2 lysimeters were consistent with that of 4 m2, but there was certain numerical deviation, deviation increased with the amount of evapotranspiration. Considering the evapotranspiration measured by 2 m2 lysimeters and 4 m2 lysimeters,there existed a fact that ET4> ET2, so in the range of allowable error, it was available to use 2 m2 lysimeters instead of 4 m2 lysimeters.(2) During the 4 growing seasons measurements in two years,1 m2 lysimeters was of poor performance. The observation had great difference with 2 m2 and 4 m2 lysimeters also fluctuated wildly. Moreover, a large amount of data was missing, so it was not suitable for using 1 m2 lysimeters instead of 4 m2 lysimeters.(3) Based on the field experiment data of winter wheat in 2013-2014 and rice in 2014, canopy resistances of winter wheat and rice were calculated using the method of effective leaf area index, canopy resistance daily variations of two crops were obtained which were to construct γc model as the measured values.(4) Canopy resistance parameters of Penman-Monteith model were optimized further. The response function of canopy resistance menace action of meteorological and environmental elements (solar net radiation, vapor pressure deficit, temperature and soil moisture) was analyzed, winter wheat and rice canopy resistance rc stress function model with the above factors was established, and the precision of the model was tested comparing with the measured evapotranspiration by the lysimeters.The results showed that the model, using the Penman-Monteith formula to calculate the amount of actual evapotranspiration of winter wheat and rice, which fitting degrees were 0.838 and 0.874 respectively, could estimate the water consumption of wheat and rice accurately...