A field study was conducted to determine canopy gas exchange rates and water use efficiency as a function of row spacing within different soil water supply conditions. Canopy apparent photosynthesis per unit of ground area increased as row spacing changed from 1.00 m to 0.33 m. However, evapotranspiration rate was only slightly different among the three row spacings within an irrigation level. Therefore, row spacing had large effects on water use efficiency which was expressed as the ratio of canopy apparent photosynthesis to evapotranspiration rate.