Abstract
The root boxes (24cm×2cm×40cm) filled with soil at two different soil bulk densities of 1.33 g/cm3 (control) and 1.50 g/cm3 (compact), were prepared for studying mutual relationship between the variation of penetration resistance as a function of soil depth and radial expansion growth of root axis. Upland rice was grown under both soil conditions for two weeks, and the root systems were sampled by pinboard method. Penetration resistance determined by a developed penetrometer showed several peaks of resistance throughout the entire depth of the root boxes caused by the presence of soil boundary layers resulting from the procedure of soil filling up. There were also found variations of root diameter of seminal axis and lst order lateral roots emerged from the seminal axis as a function of soil depth. In the compact plot, patterns of the penetration resistance corresponded well with those of root diameter. However, in the control, the correspondence of both patterns was not as clear as in the compact. These results indicated that patterns of soil mechanical impedance along the entire depth of the root box could be recorded in root axes as the history of radial expansion growth when root tips were exposed to higher mechanical impedance. The result obtained in this experiment suggested the necessity of considering the patterns of soil mechanical impedance in the growth media for the study of root-soil interaction.
