Influences of mechanical sowing and transplanting on nitrogen accumulation, distribution and C/N of hybrid rice cultivars

【Objectives】The nitrogen uptake and accumulation are an important foundation for yield formation in rice. Along with the transfer of rural labor to the cities, the pace of rice production mechanization in China consequently grows rapidly. The growth, development, and the environment of each growth stage of hybrid rice have changed in the mechanical sowing and transplanting methods. However, less research has been done on how the mechanical sowing and transplanting methods influence the nitrogen absorption and utilization characterization. The hybrid indica rice (F you 498) is used in the experiments to explore the characteristics of nitrogen uptake, utilization and C/N. 【Methods】Two factorial split\|plot designs with three replications were used in this experiment, the main plots consisted of three sowing and transplanting methods (mechanical direct seeding, mechanical transplanting, and artificial transplanting), the subplots were subjected two seeding number per hill (low seeding number per hill and high seeding number per hill). The effects of sowing and transplanting methods and seedling number per hill on nitrogen accumulation, distribution and C/N were investigated. 【Results】Mechanical sowing and transplanting methods had apparent effects on the nitrogen uptake, utilization, and C/N of hybrid rice. The mechanical direct seeding improved the nitrogen content at the jointing and maturity periods, and the capabilities of nitrogen accumulation in plants of rice at the maturity period. The nitrogen content at the heading period in the mechanical transplanting was higher than the artificial transplanting, the mechanical transplanting could keep high nitrogen accumulation of rice at the jointing period. The nitrogen translocation, apparent nitrogen translocation rate of rice leaves and stem\|sheath, nitrogen transfer rate, nitrogen use efficiency for biomass and partial factor productivity of applied nitrogen in artificial transplanting were higher than those in mechanical transplanting and the lowest in mechanical direct seeding. However, the N increase in panicle and nitrogen uptake per 100 kg of grain under different sowing and transplanting methods were different, mechanical direct seeding was the highest, followed by artificial transplanting and mechanical transplanting. Furthermore, the nitrogen use efficiency for grain production and nitrogen harvest index in mechanical transplanting were higher than those in artificial transplanting, and the lowest in mechanical direct seeding. The carbohydrate content, C/N of plant in hybrid rice at the jointing, heading, and maturity periods were significantly influenced by different sowing and transplanting methods. The mechanical sowing and transplanting methods cooperate with low seedling number per hill could enhance the C/N of different organs at the maturity period. The C/N of panicles of hybrid rice cultivar is significantly increased under the mechanical sowing and transplanting methods cooperate with high seedling number per hill, subsequently improved the carbohydrate transformation and distribution in plant. 【Conclusions】The characteristics of nitrogen accumulation and utilization of hybrid rice under different mechanical sowing and transplanting methods are different. Mechanical direct sowing and transplanting methods plus lower seedling number per hill are effective way in control and regulation of the nitrogen uptake and transfer in rice, keeping a relative high N accumulation during the whole growing period of rice, thus leading to a high N requirement for 100 kg of grain production and high yield.