SOIL CORE AND MINIRHIZOTRON COMPARISON FOR THE DETERMINATION OF ROOT LENGTH DENSITY

Detailed knowledge of the distribution of roots in the soil is importa nt in understanding the extraction of water and nutrients from soil. V arious techniques have been developed to monitor root-length density u nder field conditions. Excavation techniques, including soil cores, ha ve long been considered to give reliable estimates of root-length dens ity, but these techniques are laborious in sample collection and tedio us in determination of root lengths. An attractive alternative for mon itoring root-length density has been the minirhizotron whereby a peris cope is inserted into a clear tube permanently installed in the soil f or repeated and rapid measures of root development. The objective of t his study was to compare the ability of the minirhizotron technique to measure root-length density as compared to the root-core technique. A s in previous studies, substantial disagreement existed between the tw o techniques in the top 30-cm of the soil, The results from the minirh izotron consistently indicated a much lower root population than the r oot-core technique in the surface layer of soil. This is especially wo rrisome because more than 45% of the root-length density was found in this layer with the root-core technique. At deeper soil layers, the mi nirhizotron data pro;ed to be no less variable than the rest-core tech nique making the determination of statistically significant results di fficult. Finally, the relationship between the minirhizotron and soil- core results varied with time even when the observations from the soil surface layer were ignored. Attempts to directly translate minirhizot ron observations into a root-length density using a correlation approa ch would be suspect based on the results of this experiment.