Drip irrigation has recently been proposed as a water-saving method for rice cultivation. Growers have observed that rice yields are less under drip irrigation than under flood irrigation; however, the reason is unclear. The objective of this two-factor experiment was to compare the effects of irrigation method (flood irrigation and drip irrigation) and soil temperature (18, 24, and 30 degrees C) on rice physiology and yield. The results showed that at 30 degrees C soil temperature, drip irrigation reduced the photosynthetic activity of rice compared with flood irrigation. Drip irrigation also (i) increased the activities of superoxide dismutase by 5% and catalase by 27% and (ii) reduced endogenous hormone concentrations. At 18 degrees C soil temperature, drip irrigation significantly increased SOD (+ 7%) and CAT (+ 23%) and significantly reduced GA (- 25%) and IAA (- 16%) concentrations compared with flood irrigation. The ZR+Z concentrations were 13% less in drip irrigation than in flood irrigation at low soil temperature. The negative effects of low soil temperature (18 and 24 degrees C) were greater under drip irrigation than under flood irrigation, suggesting that low soil temperature exacerbated the stress that rice was under in the drip irrigation system. Drip irrigation significantly reduced the secondary spikelet number compared with flood irrigation. This led to a significant yield reduction. Overall, the combination of low soil temperature and drought stress may be the main reason for the marked decline in the yield of drip-irrigated rice in northern Xinjiang Province.