2022 Volume 104 Issue 2 Pages 106-110
We conducted dropping experiments of the root ball of sugi (Cryptomeria japonica D. Don) cuttings grown in multi-cavity containers in order to examine the effectiveness of root coverage of root ball surface (CRBS) as an indicator of destructive strength of container-grown root balls. Root balls of intact cuttings were dropped for three times from 1 m height, and the soil medium detached at each time was separately collected and weighed. CRBS were obtained by image analyses of the photographs of root ball surface as a percentage cover of the roots. Generalized linear models performed for the mass of detached soil medium (RDSM) demonstrated that varying soil detachment of containerized root-balls was largely explained by CRBS. The containerized cuttings showed exponential decrease of detached soil medium along the increase of CRBS as well as root mass at each of the three droppings, indicating that the CRBS is a good indicator of the destructive strength of the container-grown root balls. According to the approximated curve of against the CRBS for the ordinary condition of soil medium water content (ca.75％), 27％ or more CRBS is suggested to be a requirement for shipping in terms of securing minimum destructive strength with less than 6％ of RDSM.