Interactive Effects Of Light Condition And Nitrogen Supply On Dry Matter Production And Nitrogen Use Efficiency Of Rice (Oryza Sativa L.)

Three experiments were conducted to investigate the interactive effects of light intensity and nitrogen supply on dry matter production, yield formation, and nitrogen use efficiency of rice. In experiment 1, two hybrid rice varieties, Fengyou 998 and Peiza77, were treated by three fertilizer-N rates (0, 0.085, and 0.185 gN/kg soil) at panicle initiation and then grown in growth chambers with four light intensities (100, 250, 350 and 750 μ mol · m^-2 · s^-1) for four weeks. Leaf characteristics, dry matter accumulation, nitrogen content of organs, leaf chlorophyll content and leaf color were measured. In experiment II, The two varieties were grown in pots until heading and then treated with three fertilizer-N rates and three light intensities by shading until harvest. Dry matter production, grain yield, yield components, nitrogen uptake were measured and nitrogen use efficiency was calculated. In experiment III, Fengyou 998 were grown in field until heading and then treated with four fertilizer-N rates and three light intensities during grain-filling stage. Dry matter production, grain yield and yield components were measured. The results were as follows:1. In the growth chamber experiment, the effects of nitrogen supply (X₁,g/kg-soil) and light intensity(X₂, μ mol · m^-2 · s^-1) on dry matter accumulation (Y, g/pot) were mathematically represented by the following equation: Y =b₀+b₁X₁+ b₂X₂-b₃X₁²+b₄X₁X₂. A quadratic equation Y=b₀+b₁X+b₂X² could be used to describe the relationship between N application and dry matter accumulation of rice. Also, a linear model could be used to describe the relationship between light intensity and dry matter accumulation. It was deduced that the optimum fertilizer-N rate increased linearly with light intensity. This could be expressed by the following equation: N_opt = c₀+c₁X. This indicated that the optimum fertilizer-N rate was influenced by light intensity. Similar results were obtained in pot and field experiments where light condition during grain-filling stage was changed by shading.2. Grains yield of rice was significantly affected by shading. The grain weight of low light treatments was significantly lower than the non-shading control. As the light intensity decreased, the filled grain percentage was reduced obviously and the dry matter accumulation decreased. The production, distribution and transformation of plant dry matter were significantly affected by shading during grain-filling. Under low-light condition the export and transformation percentage of dry matter in stems and sheaths increased, and the distribution percentage of dry matter to panicles decreased compared to the non-shading control. At a given light condition, the dry matter production and yield...