Effects Of Various Nitrogen Treatments On Rice Seedlings' Growth, Caryopses Development And Ripening Grains Qualities

Pot experiments were conducted to study the effects of various nitrogen treatments on rice seedlings' growth, caryopses development and ripening grains qualities by two commonly grown rice cultivars. The main results are the following:(1) The increased nitrogen fertilizer (urea) used at the tillering stage can significantly enhance the fresh and dry weights, tillering numbers and heights of rice seedlings. The same is true for the photosynthetic rate of the rice flag leaf when topdressing was used at the heading stage.(2) Increasing the nitrogen fertilizer, especially at the heading stage, can evidently increase the numbers of free nuclei in endosperm and shorten the division cycle. At the same nitrogen treatment level, compared with Japonica, there are more free nuclei in Indica and the contrary is true for the division cycle.(3) The chlorophyll content, photosynthetic rate, and activities of CAT and SOD in caryopses decrease gradually during the rice grain filling. The topdressing ratio of nitrogen fertilizer at the heading stage is positively correlated to the physiological factors mentioned above.(4) The amylose content in the caryopses decreases gradually during the rice grain filling and the contrary is true for the protein content. Topdressing ratio of nitrogen fertilizer at the heading stage is markedly positively and negatively correlated with the amylose and protein content respectively in caryopses.(5) The fresh and dry weights of caryopses increase significantly after anthesis, 5-15d for Indica and 5~20d for Japonica, showing the curve of "S" shape, while the contrary is true for water content in caryopses. The nitrogen fertilizer treatments had no significant effect on the fresh and dry weights of the caryopses.(6) Increased topdressing of nitrogen fertilizer at the heading stage had significant effect on the development of protein bodies and amyloplasts, and the formation ofaleurone layer in caryopses.(7) Increased topdressing of nitrogen fertilizer at the heading stage can markedly improve the rice grain qualities. That is, the nitrogen fertilizer raised the ratios of brown, fine and integrated fine rice grains and increased protein content compared with the control group, while decreased the degree of opaqueness and amylose content.