Abstract: A 2-year field experiment was conducted to study the effects of rice straw incorporation into the soil on soil N supply and grain yield of rice under different irrigation systems. Results show that in early rice, late rice straw incorporation in last year increases soil NH⁺₄-N irrespective of whichever irrigation system or nitrogen fertilization is adopted.In late rice, straw incorporation of the early rice adds NH⁺₄-N to the soil only with N supply. However, with straw incorporation and N omission, soil NH⁺₄-N decreases under continuous flooding and increases under intermittent irrigation.Straw incorporation increases grain yield by 6.85% in early rice, 8.17% in later rice,9.18% with N supply and 5.83% with N omission. The development of greater number of panicles is the main reason for rice grain yield increase under straw incorporation. With straw incorporation,grain yield is highest under continuous flooding for early rice, while it is highest under intermittent irrigation for ate rice.