The water use in a conventionally-managed cotton field was observed in an arid region in Xinjiang Uygur Autonomous Region, P.R.China.
Evapotranspiration and transpiration rates of the cotton community (ET, Tr) were measured by the Bowen ratio method and the stem heat balance method, respectively. Evaporation from the soil surface under the cotton canopy was calculated by the formula: Ep = ET - Tr. Soil moisture was monitored by soil samplings.
Evaporation from the soil surface, i.e. loss of water that did not contribute to the cotton production, was substantial after irrigation. The empirically-determined interval of irrigation was too short and irrigation tended to be applied even when soil moisture was available. The amount of water supplied each time irrigation was applied was larger than that necessary for crop production, and a considerable amount of water was lost by downward percolation. A water balance calculation was undertaken for determining the suitable amount of water and interval of irrigation.