Abstract
Root research often starts from observation of root structure and morphology in soils under field conditions. Although many methods for root observations are available, most of them are yet to be standardized. Here, we recommend an improved soil profile method as the standard of root research in fields. The method requires only simple and inexpensive tools and follows simple procedures though it is a bit time-consuming. After digging a trench and clearing its soil profile, metallic cylinders are inserted into the profile at some intervals. Soils are then sampled from the profile by removing the cylinders, and roots are carefully washed out to measure their lengths/weights. By analyzing those values, we can obtain some important parameters such as root length/weight density and root depth index. For comparison of those parameters among different studies, sampling procedures need to be standardized especially how to determine the position and the direction of trench in a field because root distribution may vary with planting density. For the same reason, attention has to be paid when estimating total root length/weight per unit area by using root length/weight density. The method has a limitation in time-course analysis of root system development. Core sampling method should be combined, if necessary.
