Experimental And Numerical Study On Water,Heat And Carbon Fluxes In Cotton Fieldsunder Mulched Drip Irrigation In An Oasis

As an arid land,the region of Xinjiang has less precipitation and irrigation is the basement of the argriculture.With the develepmnt of the water saving technology,the plastic mulch and drip irrigation is widely used in the region.The plastic mulch and drip irrigation changed thesoil moisture and heat of the fieldand influenced the growth of the crop.The transport of water,heat and carbon flux of cotton field under mulched drip irrigation has different regulation.This thesis forcued on the transportation of the water,heat and carbon of a cotton field under the mulched drip irrigationin an Oasis of Korla city which was a source basin of Tarim River.The research was conductedby observed with eddy covariance systems and simulated with SIMDualKc and DNDC model.The reaserch would be a useful guide to reviel the regulation of water,heat and carbon flux in the arid land.The results of the research could havetheoretical meaning and practical value for discovering the influence of agricultral development on themigration of water,heat and carbon between the ground and atmosphereandthe irrigation management in arid lands.The thesis designedof experimentfor three years from 2012-2014 and the water,heat and carbon flux was measured with the eddy covariance systems.The average crop evapotranspiration of the growth stage in 2012-2014 was about 526 mm.Crop coefficient was calculated and the local crop coefficient curve was developed.The FAO suggested value was adjusted under mulched drip irrigation with the observeddata.The relationship between the growing days,the growing degree days and leaf area index were analised and the equations were conducted in different time scale.The adaption of the equationswas compared in different time scale and the results indicated the growing days was an enough precise parameter to estimate the crop coefficient in irrigationmanagement.The SIMDural model was used to particion the evapotranspiration and the influence of plastic mulch on the evapotranspiration was discussed.The /cT ET was about 96% and 94% in 2012-2013,individualy.The plastic mulch reduced the soil evaporation for 139.6 and 137.0 mm in the two year comared to the unmulched field.The daily and seasonly variation of the energy was analysied and the envirement facors that controled the energy was also analysised.The occurrence of threshold canopy conductance on the influence of latern heat and Priestley-Taylor coefficient.The latern heatand Priestley-Taylor coefficientincreased with,but this relation became invalid when ? 8mm/s.The variation of the carbon flux was anylised and the influenced factors were indicated.The relationships between the carbon flux and the envirement factors and the latent heat were analised in the paper.And the key parameters were obtained:the gross primary production,the net ecosystem exchange and the ecosystem respiration of 2012-2014 were-263.3 gCm^-2?870.2 g Cm^-2and 1133.5 g Cm^-2.The couping relationships of the carbon and water were reasearched from the leaf scale to the canopy scale.The influence of the envirement factors on the water use efficiency was caculated.The canopy water use efficiency was about 1-6 g Ckg^-1H2 O.The DNDC model was validated with the observed data and showed good fitness.The model was used to simulate the influence of different region and irrigation method on the carbon flux.The long term varation of the carbon flux in the Korla region from 1990-2008 was analised though the modeling results.The results showed that the net ecosystem exchange deceased but the ecosystem respiration increased,indicated the carbon sink of the cotton field became weaken.