May 15, 1919 Influence of Soil Enmronmeni on Rootrot of Tobacco 55 



POT EXPERIMENTS 



As has already been suggested, it is especially difficult to render an 

 alkaline soil acid in various degrees by the application of a theoretical 

 quantity of an acid or acid salt. The alteration produced in the soil by 

 either treatment is likely to alter it so fundamentally that comparison 

 with another soil treated in a dissimilar manner tends to complicate the 

 results to an unnecessary degree. What seems to be a considerably 

 better plan is to select a naturally highly acid soil and to change its 

 acidity to various degrees of alkalinity by the application of the theo- 

 retically correct quantities of lime. Accordingly, this plan was followed. 



The soil selected was a very acid Sparta sand from a field at Lavalle, 

 Wis. A total acidity determination of this soil by the Truog method {26) 

 showed that its lime requirement was 9.38 tons per acre. The strength 

 of acidity was found to be 108 on the basis of acetic acid at 1,000. The 

 soil after being finely screened was placed into 2 -gallon stoneware crocks, 

 perforated at the base for drainage. Ten kgm. of soil were weighed into 

 each of 36 crocks. These crocks were then divided into 9 sets of 4 crocks 

 each. The calculated quantity of precipitated calcium hydroxid of the 

 highest purity was thoroughly incorporated in the soil of each of the 4 

 crocks in each series with a view to reducing the acidity to fairly definite 

 degrees. In Table III are given the quantities of calcium hydroxid 

 applied, together with the determinations of total acidity by the Truog 

 method made several months later, when it was considered that the full 

 effect of the treatment on the soil had occurred. 



. Table III. — Influence of soil reaction on developtnent of rootrot 



Series. 



Quantity 



of lime 



added 



to 10 



kilograms 



of 



soil. 



Lime 

 require- 

 ment 

 per 

 acre. 



Average air-dry weight. 



Experiment I (White Burley). 



Experilnent II 



(Connecticut 



Havana). 



Amount of infection on 

 roots (infested soil se- 

 ries). 



In- 

 fested 

 soil. 



Unin- 



fested 



soil. 



Experiment III 

 (Maryland 

 Broadleaf).'* 



In- 

 fested 

 soil. 



Unin- 



fested 

 soil. 



3 

 4 



s 



6 



7 

 8 



9 



Gm. 



O. O 



17.80 



35- 60 



53-40 



71-25 



89.05 



106. 85 



124. 60 



142. 40 



Tons. 

 9-38 



Very slight . . 

 Considerable . 



Heavy 



....do 



....do 



....do 



....do 



....do 



Gm. 



6-35 

 2.65 

 2. 22 



•75 

 2.06 



•57 

 1.99 



•43 

 •5S 



Gm. 

 6.45 



Gm. 

 O. II 



14 

 17 

 14 

 18 

 24 

 16 



Gm. 

 6.80 

 5.00 



8. IS 

 8.67 



IO-35 

 7. 12 

 7. 10 

 5.22 

 4. go 



» Heavy infestation. 



Two pots of each series were inoculated with pure cultures of T. 

 basicola, and young seedlings of the susceptible White Burley variety 

 were transplanted into them. The first test of plant growth failed. 



