Population biological characteristics and yield of early rice of throwing transplanting under seedling-increase and nitrogen-reduction measures

The biological characteristics of population of rice 'Xiangzhaoxian 45' of throwing transplanting under three nitrogen levels N1: 105 kg(N)·hm^-2 (low nitrogen dose); N2: 135 kg(N)·hm^-2 (low nitrogen dose); N3: 165 kg(N)·hm^-2 (regular nitrogen dose) combined with 3 seedling densities M1: 0.27 million hills per hectare (regular seedling rate); M2: 0.315 million hills per hectare (high seedling rate); M3: 0.36 million hills per hectare (high seedling rate) in a split-plot trial field were compared. The results showed that treatment of high seedling rate with low nitrogen rate (N2M3) were the best combination for high yield. Plant height and growth period increased with increasing nitrogen dose, but not significantly changed with increasing seedling density. The growth period under N3 was 7.0 days and 3.4 days longer than that under N2 and N1, respectively. Tiller number increased with increasing nitrogen rate and dropped with increasing seedling density. Regression analysis showed quadratic polynomial relationship among nitrogen application rate (X₁), seedling density (X₂) and yield (Y). The ma-ximum yield occurred at Y = 8.60 t·hm^-2, corresponding with X₁ = 127.5 kg(N)·hm^-2 of nitrogen rate and X₂ = 0.48 million hills per hectare of rice seedling density, it's yield was similar to N2M3, and it was 22.7% reduction in nitrogen rate in comparison with regular nitrogen (N3). Thus the best nitrogen application rate for early rice was 127.5-135 kg(N)·hm^-2 and the best seedling density was 3.60 × 10⁵ - 4.80 × 10⁵ hills·hm^-2. The study showed that increasing seedling rate and decreasing nitrogen rate could lay the basis of early rice cultivation for maximum yield in the study area. In summary, the time contradiction between double season rice of throwing transplanting could be solved by increasing seedlings rate and decreasing nitrogen rate in early rice fields. This benefited low environmental pollution and alleviated eutrophication of water agro-ecosystems.