observations were supported by plant water potential 

 measurements in the greenhouse experiments. One 

 notable exception: the Engelmann spruce seedlings 

 grew more new roots in the granitic soil than in the 

 peat-vermiculite-sandy loam soil. 



Root dipping did not increase plant water potential 

 in any of the experiments. This finding is important 

 because the reason for root dipping seedlings on harsh 

 planting sites in the western United States is to hold 

 more available water in the seedling root zone. In 

 fact, the amount of water held by a root dip is insig- 

 nificant in the overall context of planting site water 

 dynamics, especially in dry habitat types. Magnussen 

 (1986) found that a hydrophilic gel increased the sur- 

 vival of white spruce for the first 2 weeks of drought, 

 but for no longer. Similarly, Tung and others (1986) 

 saw that hydrophilic gel delayed the first-year mor- 

 tality of Douglas-fir but did not affect season-end 

 survival and growth. 



What happens after the root dip particles dry out? 

 It is doubtful that they can pull water away from the 

 tree root system. If so, we would have seen more det- 

 rimental effects in our experiments. Instead, they 

 contract and harden. The thick slurries form a hard 

 coating. The hydrophilic gel crystals shrink to leave 

 small air pockets. 



Under moist soil conditions, some of the root dips 

 may help early seedling growth because of their higher 

 cation exchange capacity relative to the surrounding 

 soil. This would hold available nutrients in the root 

 zone. However, nutritional benefits to planted seed- 

 lings appear to be small; the root dip is dwarfed by 

 the overall conditions on the planting site. Also this 

 benefit would be short lived due to the expansion of 

 the root system. 



The granitic soil was best for mycorrhizal growth, 

 possibly because it was less fertUe. Mycorrhizal root 

 tip production differed little between the basaltic and 

 peat-vermiculite-sandy loam soils. We did not test 

 for mycorrhizal inoculum on the seedlings or in the 

 soils, nor did we inoculate the seedlings in any of the 

 experiments. However, the forest soils almost cer- 

 tainly contained inoculum, and the growth of mycor- 

 rhizae even in the peat-vermiculite-sandy loam soil 

 indicates that the seedlings brought a mycorrhizal 

 source from the nursery. 



Root dip had two observable effects on seedling top 

 growth. Seedlings dipped in the two thickest vermicu- 

 lite slurries had less shoot elongation than undipped 

 seedlings because of higher water stress. After three 

 growing seasons the lodgepole pine seedlings dipped 

 in vermiculite before being planted in the basaltic soil 

 were sbghtly larger on average than undipped seed- 

 lings, although this finding was not conclusive. Re- 

 corded precipitation at nearby Ashton, ID, was 51 

 percent above average, 28 percent above average, 



and near average for the 3 years after planting. The 

 above-average precipitation may explain why the 

 root-dipped seedlings performed well. 



Although precipitation was well above normal, sur- 

 vival dropped during the second and third years of 

 the first field experiment. Pocket gophers were re- 

 sponsible for much of the mortality. Precipitation 

 was below normal during the three growing seasons 

 after seedlings were planted in the second field ex- 

 periment. However, the results were the same: no 

 significant difference in survival due to any root-dip 

 treatment. 



Our results agree with those of Ryker (1981). He 

 reported that vermiculite and Vitera® root dips did 

 not increase survival and gi"owth of Douglas-fir, pon- 

 derosa pine, or lodgepole pine. Tung and others (1986) 

 found that Terra Sorb® did not affect Douglas-fir seed- 

 ling survival and growth. Likewise, Tuskan and EUis 

 (1991) found a Waterlock® root dip did not influence 

 ponderosa pine seedling survival and growth. Water- 

 lock® and Vitera® are hydrophilic gels much like Terra 

 Sorb® and Aquagel®, the products we tested. 



Likewise, Mullin and Hutchison (1977) found that 

 Agricol® root dip did not increase survival and growth 

 of jack pine and black spruce. The same was true 

 for slash pine seedlings dipped in Terra Sorb® (KroU 

 and others 1985) and red pine dipped in Waterlock® 

 (Magnussen 1986). Echols and others (1990) found 

 that lobloUy and shortleaf pines dipped in Terra Sorb® 

 survived better than undipped seedlings on a moder- 

 ate site but not on a harsh one. 



Our results do not fit with those of Kroll and others 

 (1985) where Terra Sorb® root dip increased survival 

 of loblolly pine on a droughty site. 



Johnson (1984) demonstrated that gel-forming poly- 

 acrylamides stored large amounts of water in sandy 

 soils. However, when this material is used as a root 

 dip, the small amount of gel adhering to the roots 

 has to give up its moisture not only to the seedling 

 roots, but also to the soil around it to reach equilib- 

 rium. With so much soil to draw off water, in a dry 

 environment the small amount of water held in the 

 hydrophilic gels can soon disappear. 



The moisture release curve for vermiculite slurry 

 is similar to that of a clay soil. Both can hold a great 

 deal of water, which is why they have been used as 

 root dips. However, under dry conditions, the fine 

 particles hold water very tightly. Although work has 

 not been done on western conifers, the hterature shows 

 that clay slurry root dips at best do not improve seed- 

 Ung survival and growth (Dierauf and Marler 1969; 

 Mullin and Bunting 1979; Sloan, in press; WiUiston 

 1967). The reason some of these studies showed clay 

 slurries to be detrimental and the reason the thicker 

 vermiculite slurry treatments curtailed root growth 

 in our study, may be due to inadequate aeration. 



10 



