Abstract: The impacts of different concentrations of chitosan (0, 20 and 40 mg·L^-1) on root growth dynamics of tobacco seedlings were measured in three soil types (ox liver soil, sand field soil, and purple soil) of Nanxiong, Guangdong Province using rhizobox device. The results showed that the rhizobox device was suitable for the observation of dynamic root growth in the three types of tobaccoplanting soils. By observing root growth on the transparent panes of the growth chamber, it was found that applying chitosan increased the total root length and root number of tobacco plants significantly in the three types of soils, and the total root length was positively correlated to the total root number. In particular, treatment with 40 mg·L^-1 chitosan showed better effects, enhancing the total root length in 20-30  and 50-60 cm soil layers of ox liver soil, and in 0-10  and 20-60 cm soil layers of purple soils, while in sand field soil, treatment with 20 mg·L^-1 chitosan was the best, increasing the total root length in 10-40 cm soil layer effectively. On day 24 after transplanting, the elongation rate of tobacco roots and the increasing rate of root number showed a growth peak under 20 and 40 mg·L^-1 chitosan treatments, being higher than those under the control. The above results indicated that chitosan could promote root growth of tobacco seedlings under soil cultivation conditions.

Key words: correlation coefficient, dependence, hydrological variability, auto-regression model, stochastic process.