Effects of nitrogen and transplanting density on the mechanisms of tillering dynamic of rice

Objectives In an attempt to provide reliable theoretical basis for reducing nitrogen fertilizer application ratein the production of rice, as well as reducing adverse effect on agricultural production owing to excessive application of nitrogen fertilizer, we studied the impact of nitrogen level and transplanting density on tillering trend of rice and further on regulating the creation of high yield group of rice by combining suitable fertilization and transplanting.

Methods Taking early-maturing late japonicas planted in the Jiangsu Area along Yangtze River and South of Jiangsu, Zhendao 11, as a pilot material, this study adopted a field experiment and a hydroponics experiment. For the field experiment, five nitrogen levels were set up in the main treatment group (N0, N90, N180, N270 and N360 kg/hm²), and two transplanting densities were set up in the secondary treatment group High density (HD), 32.5×10⁴ hill/hm²; low density (LD), 25.5×10⁴ hill/hm². For the hydroponics experiment, three nitrogen levels were set up in the main treatment group (N 5, 40 and 80 mg/kg), and two transplanting densities were set up in the secondary treatment group (12 plants/box and 24 plants/box). Through continuous record of tillers number at the tillering period, and measurement of corresponding indexes of aboveground parts of the plant samples and root system, and the impact of the nitrogen level and transplanting density, and interaction of them on physiological-ecological parameters such as biomass productivity, distribution feature of dry substance in leaves and sheath stems, concentrations of carbon and nitrogen in stems, net-light capture rate of population, and morphological feature of root system were analyzed.

Results At the same nitrogen level, compared with LD, unit area of rice reached the maximum effective number of tillering in advance on the condition of HD. Moreover, when N180 on the condition of HD, the effective tillers number of unit area reached maximum, about 290 tillers/m². However, the tillering feature of rice displayed significant difference at the middle tillering stage, and the growth feature of the plant at this stage affected its tillering capacity of next period, which resulted in population difference finally. In this case, we emphasized on analyzing the growth feature of rice in the middle period of tillering. Results indicated that tillering rate or tillers number of rice appeared significant and positive correlation with the relative growth rate of leaves and sheath stems, the distribution proportion of biomass in leaves, nitrogen concentration in sheath stems, net-light capture rate of population, number of adventitious root, surface area of root system and volume of root system; they had significant and negative correlation with carbon-nitrogen ratio in sheath stems; and the correlation with carbon concentration in sheath stems, total length of root system and number of root tips was not significant.

Conclusions Nitrogen level and transplant density affect tillering capacity of rice by regulating biomass productivity, biomass distribution proportion, nutrient concentration in plant, the utilization of aboveground population to light, the growth and development of root system. All the indexes indicate that at the same nitrogen level in the field experiment, the individual growth on the condition of LD (25.5 × 10⁴ hill/hm²) is superior to that on the condition of HD (32.5 × 10⁴ hill/hm²); but for population, HD is better for building high yield population of rice, and the required nitrogen level is about 180 kg/hm², which is lower than that on the condition of LD.