Characteristics Of Water And Heat Fluxes And Analysis Of Impacts Of Irrigation In Small Watershed And Field Scales In Paddy Fields

It is of great significance to fully understand the distribution characteristics and exchange process of water and heat fluxes,and the supply problems between rice paddy production and water resources by studying the characteristics of water and heat fluxes and the influence of irrigation on field scale and small watershed scale of paddy fields.It is also of great significance for scientific management of water resources in small watersheds,improving water use efficiency and improving agricultural ecological environment in red soil areas.In this study,paddy fields in the hilly red soil region of Sunjiaxia Watershed,Yingtan City,Jiangxi Province were selected as research objects,with large aperture scintillometer observation as the main means of water and heat fluxes in the small watershed scale,combined by bowen ratio energy balance system of field scale water and heat fluxes data and automatic meteorological station data.Based on the above data,the characteristics and differences of water and heat fluxes of double cropping paddy fields in two scales,and their correlation with environmental factors are compared and analyzed in July 2015 to October 2017.Using the method of the single crop coefficient method and the Advection-Aridity model to estimate the evapotranspiration in the paddy field and building the coupling evapotransporation model.Based on the irrigation experiment of double cropping paddy fields during grain filling stage,the effect of irrigation on the microclimate and water and heat fluxes in paddy field under different weather backgrounds was analyzed.The paper draws the main conclusions as follows:(1)Distribution of the whole growth period and different growth period of rice paddy field the energy balance components are the same,small watershed and paddy field scales similar to the net radiation flux,the sensible heat flux of the small watershed scale is greater than that of paddy field scale,the latent heat flux is the opposite of the sensible heat flux,the soil heat flux is similar to the latent heat flux.The net radiation flux of the two scale paddy fields is distributed more to the latelt heat flux,and the sensible heat flux is the second,and the soil heat flux is the least;The change of water and heat fluxes of double cropping paddy field under typical weather conditions are similar to show a single curve,which is obviously influenced by the weather conditions,and the daily accumulating value of the water and heat fluxes in sunny day is significantly greater than that of the wet weather.(2)Analysis on the relevance of water and heat fluxes of double cropping paddy fields and meteorological factors were carried out by principal component analysis and correlation analysis,showed that the daily average relative humidity,daily average temperature and daily maximum temperature are the main factors affecting the water and heat fluxes of small watershed and field scales of double cropping paddy fields in the whole growth period,however,the influence of daily minimum temperature,daily precipitation and daily average wind speed on the water and heat fluxes of paddy field in early rice and late rice was different in both scales;In typical weather,the temperature and relative humidity are the main factors affecting the water and heat fluxes of double cropping paddy fields.The influence of wind speed and precipitation on the water and heat fluxes of paddy field is different under different typical weather.Overall,the influence of wind speed is stronger than precipitation.(3)The simulation accuracy of the Advection-Aridity model is better than the single crop coefficient method in small watershed and field scale.Overall,the field scale fitting result is better than that of the small watershed,the reason for this result may be the paddy field scale underlying surface is uniform,but the small watershed scale is compound farmland,that is the difference in the uniformity of the underlying surface of the two scales.The modified parameters are modified using nonlinear fitting,and the coupling equation of the single crop coefficient method and the Advection-Aridity model is established.Testing the precision of coupling equation by the data of late rice in 2017,the results showed that the fitting results of the two scales were both better,and the decisive coefficients were all greater than 0.90.it means that the coupling equation is reasonable to calculate two scales evapotranspiration.(4)In the process of high temperature,the cooling effect of small watershed scale paddy field is slightly better than that of the paddy field scales after irrigation,the latent heat flux increases and small watershed scale was larger than the paddy field scale.The sensible heat flux decreases and the two scales were similar.At the same time,the leaf temperature decreases with the increase of transpiration,and the canopy-air temperature is low and most of them are negative.The soil water supply capacity of unirrigated paddy fields cannot meet the transpiration demand of ricee the leaf temperature rises even exceeds the temperature,the canopy-air temperature also rises and positive increase.The correlation coefficients of the latent heat flux model of irrigated paddy fields in small watershed and paddy field scales can reach 0.92.The correlation coefficients of the sensible heat flux are comparatively low,0.52 and 0.68,respectively;In the process of low temperature,the effect of irrigation on the vertical temperature of paddy fields in small watershed scale is slightly lower than that of the field scale.Rice can hold temperature by reducing the latent heat flux and increasing the sensible heat flux under irrigation,the lower the temperatre,the greater the increase of the leaf temperature,most of the canopy-air temperature are positive.The average canopy-air temperature of unirrigated paddy fields is close to 0.The sensible heat flux of unirrigated paddy fields is lower than irrigated paddy fields.The correlation coefficients of the latent heat flux model of irrigated paddy fields in small watershed and paddy field scales can reach 0.95.The correlation coefficients of the sensible heat flux are slightly lower,0.77and 0.73,respectively.