Study On Evapotranspiration And Water Use Efficiency Of Farmland And Bushwood Ecosystem

The storage of water resources has become a key issue in agricultural production and the reconstruction of ecological environments in arid and semi-arid areas.We used the eddy covariance to study the exchanges of water,carbon and energy and the mechanisms of their responses to the encironment of a spring wheat farmland in an oasis in the middle reaches of the Heihe River and woody-shrub ecosystems in semi-arid area on the northern Loess Plateau in China.We then analyzed and aompared the water use efficiencies and evapotranspiration of the two ecosystems.This information is important for the management of farmland and shrub ecosystems and for the sustainable use of water resources.The main conclusions were:(1)The radiation and heat storage flux components varied greatly both seasonally and diurnally within and between the two ecosystems.The sensible and latent heat fluxes were the main consumption terms of the net radiation.The proportion of soil energy storage flux of the net radiation was highest in the 0-5 cm layer in both ecosytems.The energy storage flux of the atmosphere accounted for a larger proportion of the net radiation in the farmland ecosystem,but the proportion of was relatively small for the woody-shrub ecosystems.(2)The energy fluxes in the farmland and shrub ecosystems were not closed.After considering the heat storage fluxes,the energy closure could be increased obviously.The contribution of the soil storage flux to energy closure was between 9.45 and 13.73% for both exosystems.That of latent heat storage is 2.96% for the spring wheat ecosystem,while in shrub ecosystem reduced the energy closure by 0.06%.(3)Evapotranspiration and water-use efficiency varied both seasonally and diurnally within and between the two ecosystems.Net radiation,air temperature,mean soil temperature and humidity to a depth of 60 cm,vapor pressure deficit and leaf area index all influenced evapotranspiration and water-use efficiency to some degree,and varied greatly between the ecosystems.(4)Evapotranspiration increased statistically after rain,but hysteretically.The increased amplitude and the days of lagged of evapotranspiration were affected and restricted by the amount of precipitation and duration of precipitation.The spatial and temporal distribution of precipitation determined the amount and seasonal distribution of evapotranspiration in the shrub ecosystem.(5)About 273.41 mm of irrigation and precipitation water was used in the farmland ecosystem to supply moisture below the 0-60 cm soil layer or groundwater.Evapotranspiration was higher than precipitation in the Caragana shrub ecosystem,so water supplementation is needed.However,evapotranspiration was lower than precipitation in the Amygdalus pedunculata ecosystem,so the supply of water was sufficient to meet the demand.