BLACK KOOT-ROT OF TOBACCO 



121 



Table 2. — Efi'ECts of alujiinuji sulfate alone axd with sulfuric acid or 



SULFint ox pH values OF SOIL AND ON GROWTH AND BLACK ROOT-ROT 

 OF TOHACCO IX LIMED SOIL. 



pH values of soil 



Soil treatment After After After 



(Grams per pot) 2 weeks 11 weeks 18 weeks 



Ci.crk (5.-2 bj) 5^9 



Sulfuric acid 5.9 5.2 5.1 5.2 



Sulfur 1.9 5.5 5.3 5.3 



Aluminum sulfate 4.4 ^ 5.0 5.0 5.1 



Sulfuric acid 5.9 ^ 



Aluminum sulfate 4.4 ^ 5.3 5.1 5.2 



Sulfur 1.9 ( 



Aluminum sulfate 6.5 1 4.9 4.9 5.3 



Sulfuric acid 5.9 ( 



Aluminum sulfate 6.5 ) 5.2 4.8 4.8 



Sulfur 1.9 I 



Aluminum sulfate 4.4 5.5 5.5 5.7 



Aluminum sulfate 6.5 



Dry weights 

 per plant* 



Relative Black 

 Grams numbers root-rot 



* Means for duplicate treatments. 



i\luminiun .sulfate ii.sed alone re.siilted in no significant increase in dry 

 weiglit of i)lants; in fact, tlie lieavier application interfered with growth. Dry 

 weights of plants were increased 28 per cent by sulfuric acid and 24 per cent 

 by sulfur; but this same ajjplication of sulfur when used with aluminum sul- 

 fate resulted in an increase in dry weights of j^lants of 42 per cent. 



It appears from this that aliuninum sulfate added to the soil had an un- 

 favorable effect on Tbielavia basicola, and that the effect on the disease which 

 this fungus causes was greater when the soil acidity was further increased 

 as bv the use of sulfur. 



With Sulfuric and Orthophosphoric Acids Used Together 



The pH value of soil was lowered as nmch by sulfuric or nitric acid alone 

 as by the use of either of them with orthophosphoric acid; but tobacco grew 

 better when orthophosphoric acid was used with sulfuric or nitric acids than 

 when either of the last two named acids was used alone. In the preliminary 

 experiments there was rather less black root-rot when sulfuric or nitric acid 

 was used alone than when either of them was used with orthophosphoric acid, 

 but this effect of the latter was more than offset by the improved growth of 

 the plants. 



On the basis of these experiments it was decided to use (together) sul- 

 furic acid, 1800 pounds per acre, and orthophosphoric acid (80 per cent), 440 

 pounds per acre, in the field experiments subsequently described. The quanti- 

 ty of a-jidifying chemical necessary to apply to a soil in the field to cause a 



