| The study on the water and heat transfer law,control mechanism and evapotranspiration water consumption of rice field ecosystem was conducive to the improvement of crop water productivity and irrigation management of farmland or watershed.In this paper,Liujiazhan farm in yujiang county of Jiangxi province was taken as the research area,and the paddy ecosystem was taken as the research object.Based on the observation data of vorticity correlation system,Bowen comparator and meteorology data which were carried out in the double season paddy field.The time distribution of water and heat flux,energy closure,evapotranspiration characteristics and its response to environmental factors for early and late rice were analyzed.At the same time,about the evapotranspiration simulation,Penman-Monteith and Shuttleworth-Wallac evapotranspiration models involve canopy resistance,Jarvis,Irmak and Stannard canopy resistance models were applied to PM and SW model,and the canopy resistance model with higher precision and most suitable for rice in the research area was selected.The conclusion of this paper as follows:?1?The peak value of average daily variation of net radiation flux of early rice and late rice in growth period appeared in different growth periods,and their seasonal variation characteristics showed fluctuating upward and downward trends respectively.The variation tendency of latent heat flux kept pace with net radiation.The latent heat flux of early rice was higher in mature stage,while that of late rice was higher in vigorous growth stage and lowest in mature stage.The variation tendency of sensible heat flux was opposite to latent heat flux.The fluctuation range of soil heat flux for early rice and late rice was small.The daily change of energy distribution ratio between early rice and late rice were different due to the change of growth stage.The LE/Rn of early rice in mature stage was higher than other growth stage,and the H/Rn in regreening-tillering stage was slightly higher than other growth stage.The LE/Rn of late rice was the highest in the jointing and booting stage;H/Rn was significantly higher in the middle tillering and maturity stage.There was no significant change in G/Rn.?2?The energy closure of rice fields at night was poor,and the energy closure in daytime was higher than that in all-day time.The energy closure of late rice at daytime was 77.9%,which was higher than that of early rice?70%?,and the two were close in the whole day.The energy closure degree of late rice was obviously better than early rice.The energy balance residuals of early rice and late rice in different growth periods were reduced when the soil heat storage was corrected to the surface.The OLS linear regression slope of early rice and late rice increased,energy closure increased by 7.2%and 10.6%respectively.The energy balance ratio of late rice increased from 0.782 to 0.842,with a higher increase than that of early rice.?3?The diurnal variation curve of ET in sunny day was smoother than that in cloudy day,and the total ET in typical sunny das in each growth period was significantly higher than that in cloudy day.The seasonal variation of daily ET of early rice was opposite to that of late rice.The control mechanism of evapotranspiration was studied by geographical detector statistical method.The results showed that the contribution rate of relative humidity,wind speed,net radiation and saturated vapor pressure difference to rice ET was significantly greater in sunny day than in cloudy day.The contribution rate of many environmental factors to the daily ET of late rice was significantly higher than that of early rice,while net radiation and soil temperature had more significant effects on early rice.There was an interactive relationship between different environmental factors,and the contribution rate was greater than their individual contribution rate,of which the interactive contribution rate of net radiation and environmental factors was the highest.The relationship between rice field ET and canopy conductance showed a power function growth form.When canopy conductance was less than 10 mm·s-1,ET increaseed rapidly with the increase of canopy conductance.?4?Jarvis models with eight different combination forms of stress functions were combined with PM model,and the simulation accuracy varied to different degrees.The PM?Jarvis and PM?ST model were obviously underestimated in the initial stage of rice tillering stage,while the simulated value of PM?Irmak model in all growth stages of rice was close to the dynamic value of daily evapotranspiration.The root mean square error and average absolute error of PM?Irmak model were smaller than those of PM?Jarvis and PM?ST model,the determination coefficient,nash efficiency coefficient and consistency index were closer to 1,and the overall simulation effect was the best.For the Shuttleworth-Wallace model,it has the best simulation effect when Jarvis was applied to SW model.PM?Irmak and SW?Jarvis models are most sensitive to canopy resistance. |
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