Abstract: To provide theoretical basis for high yield and benefit of doubleseason early hybrid rice, we examined the effects of nitrogen (N) application rate and the number of transplanting seedlings per hole on the yield, yield components, and nitrogen use efficiency of doubleseason early hybrid rice. The experiment used a completely randomized block design, including five N application levels (0, 120, 150, 180 and 210 kg·hm^-2, expressed as N₀, N₁, N₂, N₃ and N₄ respectively) and three levels of seedlings per hole (2, 3 and 4 seedlings per hole, expressed as M₁, M₂ and M₃ respectively). We investigated the dry matter, leaf area index, grain yield and its components, N uptake, N use efficiency in the mature period of rice. The results showed that both N application rate and seedlings per hole had significant effects on doubleseason early rice yield. Rice yield had a significantly positive correlation with panicle number and grain number per spike, and a significantly negative correlation with seed setting rate and 1000-grain weight. With the increases of N application rate, total N accumulation in rice increased, but the N agronomic efficiency, N partial factor productivity, N internal efficiency and N harvest index decreased. The absorption and utilization efficiency of N fertilizer and yield increased at first and decreased later with the increases of N application rate. With the increases of seedlings per hole, the agronomic efficiency of N decreased. A proper amount of seedlings could increase the total dry matter and yield to improve the N use efficiency. Compared with other treatments, the combination of 180 kg·hm^-2 of N application rate and 3-4 seedlings of per hole could get higher yield and N use efficiency. Suitable amount of N application and seedlings per hole could produce a significant increase in effective panicle number, yield and total N accumulation. Nitrogen fertilization rate was recommended as 180 kg·hm^-2 for the early rice with the transplanting density of 3-4 seedlings per hole.

Key words: rhizosphere effect, warming, polyphenoloxidase, alpine scrub, catalase