Table 6. — Properties of soils at respective nurseries 



Cation 



Particle size distribution exchange Organic 



Nursery 



Soil Type 



Sand 



Silt 



Clay 



ph 



capacity 



matter 









- Percent - 







meq/100g 



Percent 



Montana State 



Sandy loam 



57 



30 



13 



6.9 



11.76 



2.7 



Mountain Home 



Loam 



40 



50 



10 



5.6 



13.67 



4.5 



Coeur d'Aiene 



Sandy loam 



71 



21 



8 



6.1 



6.17 



3.1 



Lucl<y Peak 



Sandy loam 



61 



26 



13 



5.8 



7.44 



1.7 



Mt. Sopris 



Sandy loam 



55 



29 



16 



6.0 



9.87 



3.3 



Albuquerque 



Sandy loam 



73 



20 



7 



7.4 



5.98 



.4 



Color and morphology of ectomycorrhizal short roots 

 and other aspects of root structure were similar on the 

 species examined at the respective locations within the 

 limits of variation of sample seedlings. As would be 

 expected, differences occurred in root structure and num- 

 bers of ectomycorrhizal short roots on seedlings from 

 different nurseries. Since these differences were not 

 related to the treatments of interest, they were not con- 

 sidered in the analysis. Table 6 documents general soil 

 characteristics at each nursery. 



DISCUSSION AND CONCLUSIONS 



The lack of strong, consistent relationships between 

 herbicide treatment and numbers of ectomycorrhizal 

 short roots indicate a relatively unpredictable risk factor 

 associated with these herbicides and ectomycorrhizal de- 

 velopment. The strong relationships within nurseries, 

 both positive and negative, between herbicide-treated 

 seedlings of particular species and numbers of 

 ectomycorrhizal short roots clearly demonstrate highly 

 individualistic responses. Soil differences between nurser- 

 ies may contribute to individualistic responses and were 

 likely responsible, at least in part, for between-nursery 

 differences in mycorrhization. However, with regard to 

 mycorrhizae and herbicides, the soil characteristics we 

 measured showed no unusual differences at nurseries 

 where stronger relationships were observed. Accordingly, 



each combination of herbicide, seedling species, and 

 nursery should be evaluated for possible negative effects. 



With the three herbicides investigated here, the most 

 dramatic reductions were from herbicide treatments on 

 Douglas-fir at the Montana State Nursery, which aver- 

 aged 32 percent. This reduction is probably not enough 

 to cause substantial losses in seedling quality. It does 

 suggest that Douglas-fir may be a sensitive species. The 

 bases for such individualistic responses at a particular 

 nursery are not clear. Because of the lack of explanation, 

 due caution should be exercised vdth all herbicides. 



The lack of strong herbicide-induced reductions and 

 frequent increases in ectomycorrhizal development agree 

 with other experiences (Trappe 1979. 1983; South and 

 KeUey 1972; Ogawa and Yambe 1980; Palmer and others 

 1980; Greaves and others 1976; Iloba 1974. 1976. 1977; 

 UhJig 1966). Thus, use of these herbicides for nursery 

 weed control in Central and Northern Rocky Moimtain 

 nurseries does not appear to pose high risks to 

 ectomycorrhizal development. The combinations and timing 

 of application tested here could be used in all cases, but 

 with reservations on Douglas-fir. All herbicides and ap- 

 plication procedures should be used on this species only 

 with great caution, particularly at the Montana State 

 and Coeur d'Aiene nurseries. Even in relatively risky 

 combinations, herbicide use should not be precluded if 

 growth or outplanting performance of seedlings do not 

 suffer. 



6 



