Effects of seeding rates and nitrogen fertilizer managements on photosynthetic productivity and nitrogen utilization in direct-seeded rice
Due to the climatic feature of low light, small temperature difference and high humidity, transplanting rice was the major pattern in rice production in Sichuan Basin.As the rural labor force was decreased and the new types of rural management body were developing rapidly, the development of direct-seeded rice has becoming increasingly concerned.With the further development of direct seeding technology, direct seeding technique of rice has been successfully applied in 12 provinces and cities in China, which showed a significant role in improving the production and efficiency.In terms of the particular climate, topographic condition, and the hybrid rice in Sichuan Province, there were few studies on direct-seeded rice.Many researches had been done on the growth and development in direct-seeded rice under mechanical dry direct seeding and precision hill-direct-seeding, but the nitrogen management in those studies was according to the high-yield cultivation management of transplanting rice,and whether the nitrogen fertilizer management of transplanting rice was appropriate for direct-seeded rice was undefined.Seeding rate could immediate affect the population quality of rice plants and grain yield.The former researches often used the conventional rice as material but not the hybrid rice, so, further studies on the effects of seeding rate and nitrogen management on the dry matter production characteristic, nitrogen absorption and utilization law in direct-seeded hybrid rice were necessary.Hybrid rice 446A/518 was used to investigate the effects of seeding rate and nitrogen fertilizer management on the photosynthetic productivity, dry matter accumulation and translocation, nitrogen absorption and utilization under manual wet direct-seeding, and the correlation among the three which are photosynthesis index, grain yield and nitrogen utilization efficiency of rice plants were also taken to analyze.The results indicated that increasing the seeding rate would enhance the leaf area index during jointing stage and promote the nitrogen accumulation, nitrogen use efficiency (NUE) for biomass production and NUE for grain production.However, the leaf area index (LAI), SPAD value, photosynthetic rate, dry matter accumulation and translocation, partial factor productivity of applied nitrogen and NUE firstly increased and then decreased with the increasing of seeding rate.From the views of nitrogen management, the nitrogen fertilization for heading sprouting of 40％ (N2) would obtain the highest LAI during jointing stage.Adding the nitrogen fertilization for heading sprouting was beneficial to increase LAI after heading stage and promote photosynthetic rate, dry matter accumulation and nitrogen accumulation, enhance substance accumulation and turn-over capacity and nitrogenabsorption and nitrogen utilization efficiency under the seeding rates of 15.0 or 22.5 kg/hm2.Moreover, when the seeding rate was added up to 30.0 kg/hm2, through antedisplacement of nitrogen would avail the nutrient absorbability of rice and promote substance accumulation and turn-over capacity and improve the NUE.Correlation analysis indicated that both the photosynthetic efficiency and LAI during heading stage were significantly correlated with grain yield, nitrogen-absorbing ability and nitrogen-utilizing efficiency of rice plants.In summary, when the seeding rate was 22.5 kg/hm2 and the ratio of nitrogen application at transplanting stage, tillering stage and booting stage were 40％, 10％, and 50％, respectively, it would lead to gain the relatively high grain yield and higher photosynthetic efficiency, dry matter production capacity and nitrogen utilization efficiency.
seeding ratenitrogen fertilizer managementphotosynthetic productivitynitrogen uptakenitrogen use efficiency
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