Effective root growth potential of jack pine (Pinus banksiana Lamb.) container stock

Abstract

The effective root growth potential (RGP) of both potted and outplanted jack pine seedlings grown in Lannen-Sokeri FH-408 paperpots and Can-Am #2 Multipots was measured on three test dates during the summers of 1986 and 1987. Effective RGP refers to the potential of outplanted container seedlings to extend new white roots into the surrounding soil. In 1987 two crop types, overwinter and current crops, were also compared. Effective RGP was measured in three zones: 1, the upper half of the cylindrical area containing the container plug; 2, the lower half of the same area; and 3, the bottom of the plug. The number and length of white root tips projecting from the plug were counted and measured to determine root number (RN) and total root elongation (TRE) in cm from each zone for each container type. Seedlings grown in the Can-Am #2 Multipot had a significantly higher effective RGP than seedlings grown in the FH-408 Paperpot at all three test dates for both data sets in 1986 and 1987. Effective RGP was highest from root zone 3 for seedlings grown in both container types. The overwinter crop also had a higher effective RGP than the current crop seedlings. This difference was significant only in the potting trial. The morphological development of the three crops of seedlings used in this study was also monitored. Seedling height, root collar diameter and shoot and root dry weights were measured at two week intervals throughout the greenhouse production phase. The Can-Am #2 Multipot stock showed both superior morphological characteristics and regenerated far more roots after outplanting than stock grown and outplanted in Japanese Fh-408 Paperpots. The results of this study support the hypothesis that seedlings grown in a container-free plug system such as the Can-Am #2 Mulitpot which are planted with an unrestricted rootball will exhibit a higher level of root egress as expressed by higher effective RGP values than those seedlings grown in the FH-408 Paperpot which are planted with the paper barrier of the container still surrounding the rootball. It is recommended that serious consideration be given to converting from the use of restrictive containers like the FH-408 Paperpot to container-free plugs for the production of forest tree seedlings. Some recommendations for future research are also made.