Abstract: Taking early rice variety Luliangyou 996 and late rice variety Y-liangyou 86 as test materials, a field experiment with 4 nitrogen (N) fertilization rates and 3 transplanting densities was conducted to study the effects of N fertilization rate and transplanting density on the plant dry matter accumulation, canopy solar energy interception rate, grain yield and its components of double season super hybrid rice. A single peak curve relationship was observed between the N fertilization rate and grain yield of test varieties. A medium N fertilization rate could obtain the maximum yield, with 10245.04 kg·hm^-2 for Luliangyou 996 and 11015.37 kg·hm^-2 for Y-liangyou 86. The effective panicles increased with increasing N fertilization rate, but the filled grain number per panicle
reached the peak at medium N fertilization rate (N135 for Luliangyou 996 and N180 for Y-liangyou 86), with the grain·panicle^-1 being 143.92 and 142.80, respectively. Transplanting density had minor effects on the grain yields of both Luliangyou 996 and Y-liangyou 86 and the yield components of Luliangyou 996, but had significant effects on the effective panicles and seed setting rate of Y-liangyou 86. High transplanting density induced high effective panicles but low seed setting rate, while low transplanting density was in adverse. The interaction of N fertilization rate and transplanting density had no significant effects on the grain yields of Luliangyou 996 and Y-liangyou 86, but, in terms of high yielding and high fertilizer N use efficiency, the optimal N fertilization rate for Luliangyou 996 and Y-liangyou 86 was 135 and 180 kg·hm^-2, and the optimal transplanting density for Luliangyou 996 and Y-liangyou 86 was 45×10⁴ and 30×10⁴ clusters·hm^-2, respectively.

Key words: Riverine organic carbon, Terrestrial ecosystem, Global carbon cycle, Drainage erosion, Radiocarbon, Anthropogenic activities