SEEDLING GROWTH 



METHODS 



The effects of soil fumigation on seedling development have been evaluated by 

 observation and by measurement of the following characteristics on three to four ran- 

 domly selected groups of 10 seedlings from both fumigated seedbeds and their paired, 

 unfumigated controls: 



Height of shoot 



Weight of shoot (ovendry basis) 

 Stem diameter (at root collar) 

 Shoot-root ratio (by weight) 

 Weight of roots (ovendry basis) 

 Root area index ^ 



Most of the results are based on the 1963 fall fumigation trials at Coeur d'Alene and 

 Savenac. Only those fumigation treatments which seemed to have provided the most 

 effective pest control and the best growth responses were included in the sample 

 measurements . 



EFFECTS ON SEEDLING SIZE 



Soil fumigation at Savenac and Coeur d'Alene has caused a variety of seedling 

 growth responses ranging from a definite depression of growth to substantial increases 

 in seedling size. In the 1963 spring fumigation, for instance, a number of treatments 

 caused reduced growth and seedling chlorosis. There were no obvious increases in 

 seedling growth resulting from spring fumigation. 



In the 1963 fall-fumigation trials, measured seedlings provide results ranging 

 from "no-effect" to substantial and significant increases in the size characteristics 

 of 2-0 and 3-0 seedlings (figure 3 and table 4). In general, seedlings grown in 

 fumigated soils were larger than those from unfumigated soil. In about 22 percent of 

 the individual comparisons which were made, this difference proved significant at the 

 95-percent level of probability or greater. There were not enough differences in the 



■^A technique (similar to the "root titration" measurement used by many nursery 

 workers) in which the relative surface areas of root systems are determined by dipping 

 the roots in a dilute water-india ink suspension, draining, washing the roots in water, 

 and colorimetrically measuring the amount of ink transferred. The recorded difference 

 in light transmittance is the "root area index." 



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