generally smaller than seedlings grown at low density in unfumigated soil. Thus, in 

 this extreme case, the density effects have completely concealed the true fumigation 

 effects. If all of the size comparisons could have been made at common densities, both 

 the magnitude and number of significant differences in seedling size would probably 

 have been greater. 



In general, the increases in seedling size characteristics associated with soil 

 fumigation can be considered beneficial. Seedlings grown in fumigated soil are general- 

 ly large enough to outplant at an earlier age than those from unfumigated soils. Even 

 ponderosa pine, which showed no increase in size in the 1963 fall-fumigation tests at 

 Coeur d'Alene, has responded to subsequent operational fumigation with improved growth 

 and a higher percentage of trees developing fascicled needles during the first growing 

 season. This improved growth has permitted the shipment of 1-0 ponderosa pine stock. 

 Production time for Engelmann spruce stock has been shortened by 1 year, and some 1-0 

 Douglas-fir may be plantable. A 1-year reduction in time to produce seedling stock is 

 equivalent to a cost savings of $3 to $4 per thousand or $3,000 to $4,000 per acre. 



In one respect, however, the increased seedling growth may be detrimental. Seed- 

 lings from fumigated soils consistently have higher shoot-root ratios than those from 

 unfumigated soil (table 4), indicating a poor "balance" of tops to roots. This has 

 resulted not from a decrease in root weight, but rather from a proportionately greater 

 increase in top weight than root weight. It seems that this effect may be, at least 

 partially, an artifact resulting from standard lifting depth and root-pruning lengths, 

 regardless of seedling size. Just how high the shoot-root ratio can go before it re- 

 duces field survival and growth is not known. To limit the development of high ratios 

 in fumigated soils, nurservmen might wish to place greater emphasis on cultural prac- 

 tices such as root pruning in place or "root wrenching." 



The reasons for improved seedling growth in fumigated soils are not clear. It is 

 unlikely that the improvement can be attributed to reduced weed competition since both 

 fumigated and unfumigated beds were kept relatively weed free. Reduced populations of 

 soil organisms may have resulted in better nutrition of seedlings--or in a reduction of 

 sublethal infections which could reduce growth without killing the seedlings. 



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