Water And Energy Balance Of Irrigated Field In The Middle Basis Oasis Of Heihe River

Based on the combination of eddy covariance system and soil physical experimental method, researches were conducted to determine the water and energy balance in the wheat fields located on the middle oasis of Heihe River, which is the second largest inland river in China. The results showed that the net radiation(Rn) was closely related to the vegetation coverage over the surface. As the increase in vegetation coverage, the Rn became large. Conversely, the reflected short-wave radiation decreased with coverage increase. The largest shortwave reflectance presented at the winter irrigation later because of the freezing effect of irrigated water on the earth surface. During growth period of wheat, the sensible heat fluxes(H) stayed in a relatively stable state. The H were controlled by the solar radiation and filed cover situation. In net radiation flux, the proportion of H was no more than 20%. Opposite to the sensible heat fluxes, the latent heat fluxes(LE) showed the variation trend from low to high and then reducing. Moreover, the LE consumed the most of the net radiation energy with a proportion more than 60%. The soil heat fluxes present two protuberances over time in a year. One was at the beginning of growth period and another was at the end of this period. According to the observation from the eddy covariance system, the energy closure during growth period was in the range of 0.72-0.82. The largest value of closure emerged at the time of the maximum value of leaf area index(LAI). The main factors influencing the energy closure included the topography, equipment precision, meteorological conditions and data processing. Additionally, the arbitrary ignoring of the heat storage fluxes term in energy balance function was one of the important causes to reduce the energy closure. After considering the heat storage fluxes, the energy closure increased more than 10%.The main water sources for the wheat field during growth period were from the precipitation and irrigation. Among, the irrigation was the leading approach accounting for 90% percent. The main water supply for the idle period of wheat field were the precipitation and groundwater. The water from groundwater accounted for 70% in the whole water supply in this period. During winter, the water stored in the soil were mostly from the winter irrigation occurred in the middle of November. After winter irrigation, there were about 50% of the irrigated water stored in the soil porosity with a solid phase. The main consumption ways of supplied water in such field were evapotranspiration(ET) and deep infiltration. The results showed that more than 75% supplied water was consumed by ET and 19% water were consumed by infiltration. There was about 6% water consumed by soil water storage and vegetation body. According to the portioning result from the CO2-H2 O fluctuation correlation model, the transpiration flux took the most contribution to ET. The ratio of T/ET was 72%. From the portion of each consuming approaches, approximately half supplied water was consumed by evaporation and deep infiltration ineffectively instead of absorption by crops. The non-available water was a great waste of resources in arid inland river basin with limited water resources. The sequential studies was necessary to improve the irrigation mode.