[Dynamic changes of morphological parameters of tobacco root in field]

The study with rhizotron showed that the total length of tobacco's second order lateral root had a much more increase than that of first order one, and the root length developed rapidly during 26 to approximately 40 d and 56 to approximately 70 d after transplanting for the second and first order lateral root, respectively. Before tip pruning, the branch root density of tobacco was decreased in order of 10 to approximately 20 > 0 to approximately 10 > 20 to approximately 30 > 30 to approximately 40 cm soil layer. The branch density of main root was the highest in 7 to approximately 21 cm soil layer. The deeper the soil layer, the bigger the ratio of dry weight and root length, but the distribution was reverse at 90 d after transplanting. The first order lateral root length density distributed in "S" curve in 0 to approximately 10 cm soil layer and in double climax curve in 10 to approximately 20, 20 to approximately 30 and 30 to approximately 40 cm soil layers, while the second order lateral root length density became bigger with the course of growth period, which was in "S" curve in 0 to approximately 10 cm soil layer and in single climax curve in other soil layers.