In situMeasurement of Rooting Density by Micro-Rhizotron

Abstract

Measurement of the root system is becoming increasingly important to investigate the soil-plant system. A practical method to measure root length, the line intersection method was developed by NEWMAN (1966). The method can be applied for measure. ments of the root growth behind the observation window of a rhizotron (HEAD, 1966) but it does not afford an evaluation of the rooting density in bulk soil (BOHM, 1979). The objective of the current report is to examine the relationship between the root length on the observation window and rooting density in bulk soil and to develop a new method to measure the rooting density in situ based on a plausible theory. Some attempts were already made to relate the root length on the observation window with the rooting density in bulk soil. TAYLOR et al. (1970) measured the root length on the window and attempted to calculate the rooting density in bulk soil assuming that all roots within 2 mm of the observation panel were visible. It was also assumed that the rooting density in the soil near the observation panel was not high compared with that of the bulk soil. These two assumptions however, may not always be valid. Visible distance may change with the nature of soil. The rooting density may not remain uniform if the species and growth conditions of the plant vary. TAYLOR and BOHM (1976) found that root concentration can be considerably increased in the soil near the observation window. The mini-rhizotron was used to estimate the rooting density in the bulk soil (SANDERS and BROWN, 1978). Similar assumptions were made also and may not be valid either. It was assumed that the visible distance, was' 3 mm in this case, that is I.S times the value postulated by TAYLOR et al. (1970). As the root concentration can be 3 times higher in the 2 mm soil layer immediately behind the mini-rhizotron window (BOHM, 1979), BOHM et al. (1977) concluded that the mini-rhizotron should not be used for rooting density studies. But the author considers that it is possible to determine the rooting density based on the root length on the observation window if a tube with a very small radius is