Abstract: In order for the sound management of high water use efficiency agriculture, the characteristics of energy partitioning and water transfer in winter wheat field are explored in detail. Micrometeorological and soil moisture data for the research were collected at Yucheng Experimental Station, Chinese Academy of Sciences from recovering to maturity period in 1992. Bowen ratio is shown much larger before irrigation than after irrigation and its average value in midday (11∶00—15∶00) highly correlates with aerodynamic resistance (r^a). The correlative coefficient is 0 72 which is much more notable than that with net radiation and that with soil moisture. Ifr^ais smaller, the vapour in the crop canopy is easier to be transferred into the atmosphere, which will largely stimulate the water lose processes of crop, and Bowen ratio becomes less and vice versa. Albedo is larger before irrigation than after irrigation. The daily maximum albedo, which is 0 21—0 24, appears at booting period, thereafter gradually going down and reaching 0 15—0 16 at maturity period. And then it turns to slightly increase because of the leaves dying gradually. From recovering to maturity period, that is, from March 20 to May 30, statistically, daily evaporation increases from 3mm/d to 5mm/d, the difference is 2mm/d. Daily net radiation increases from 4 3mm/d to 7 4mm/d. The difference is 3mm/d which is larger than that of daily evaporation. Also from recovering to maturity period, the total evapotranspiration estimated by Bowen ratio energy balance is 297mm. Considering the drainage from irrigation or precipitation to groundwater and evaporation from groundwater to atmosphere through groundwater table variation and groundwater supply capability, the evapotranspiration taken as the residual of water balance equation is 302mm. The minor difference of the two, to a certain degree, shows that it is reliable to use water balance equation to estimate cumulative evapotranspiration. Surface resistance is stable and low at midday while variable and high at dawn and dusk. The difference before and after irrigation is up to 20s/m. Because the meteorological conditions of the two cases are almost the same, this difference is mainly due to soil moisture turning from the deficit to the saturated. The average midday surface resistance is largely dependent on air saturation deficit which is shown to be one of the key factors controlling the opening and closure of stomata. Whether soil surface is fully covered by crop or not is important to the relationship between surface resistance and surface soil water status. There is one irrigation event at March 30 when crop does not fully cover the soil surface and field evaporation mainly comes from soil. It is seen that before irrigation, surface soil is in dry status and evaporation is highly supressed, so surface resistance raises to 80s/m. After irrigation, soil surface is wet, surface resistance then falls down, just 10 to 20s/m. No such obvious changes can be observed after soil surface covered by crop. Generally, surface resistance increases slowly with growth stage which corresponds to the increase of stomatal resistance due to the canopy leaf evolving processes from living to dying.

Key words: energy balance, reflectivity, albedo, surface resistance