Effects of physical characteristics of rooting media on the rooting of Cryptomeria japonica cuttings

In the present study, we evaluated the effects of rooting medium, which is one of the environmental factors, on the rooting of C. japonica cuttings. The relationship between the physical characteristics of 12 media types and the rooting traits of cuttings of three different clones was analyzed under mist irrigation. Using principal component analysis of the data on physical characteristics of the media, we observed that the media could be classified according to two axes: permeability and retentivity of water. The rooting percentages and root lengths differed for the different media. Besides, using generalized linear mix modeling, a model including the air : water content ratio and its quadratic term as explanatory variables was determined to be the best, based on the deviance information criterion values. The model predicted that the rooting percentage peaked at an approximate air : water content ratio of 1. 0. On matching the small particle size kanuma-soil and coconut fiber to the best air : water content ratio, the root length in kanuma-soil was observed to be longer than in coconut fiber. These findings suggest that the air : water content ratio is a good indicator of the rooting percentage and small particle size kanuma-soil is suitable for the propagation of C. japonica cuttings and for evaluating the rooting traits of the cuttings under mist irrigation.