BLACK HOOT-HOT OF TOBACCO 135 



limited, whicli is probably fortunate if sulfur is to be of use in tiie protection 

 of tobacco against black root-rot. 



The effect on burn of tobacco of applications of sulfur to soil limed and 

 net limed may be seen by reference to Table 8. 



The fire-holding- capacity of the tobacco on limed plots was reduced by 

 tlie acidification treatments in 1926, the first year of their application and a 

 year of relatively jtoor burn on all plots. In 1927, the burn of tobacco on 

 limed plots was improved by sulfur, 200 pounds per acre applied in 1926, or 

 in 1926 and 1927, and by sulfuric and orthophospiioric acids applied in 1926; 

 it was not affected significantly or consistently by sulfur, 400 pounds per 

 acre applied in 1926, but it was somewhat injured l)y sulfur, 400 pounds per 

 acre applied in 1926 and 1927, and by the acids ai)i)lied in the two years. In 

 1928 the burn of the tobacco on limed plots was either improved or practical- 

 ly unaffected by all the acidification treatments. In 1929 the fire-holding 

 capacity of the leaf on limed plots was not reduced by the acids or b}^ sulfur 

 one year, but sulfur, 400 pounds per acre for two years, was associated with 

 a poorer burn. 



Considering now the burn of the tobacco on plots not limed, it appears 

 that in 1927 tiie fire-holding capacity was reduced somewhat, although not 

 consistently, by all the acidification treatments except the smallest application 

 of sulfur; in 1928 it was either improved or practically unaffected by the 

 acidification treatments; and in 1929 it was somewhat reduced by all acidifica- 

 tion treatments. 



However, applications of sulfur such as these would be nuide only to 

 limed soil and when black root-rot made such treatments advisable; and when 

 there were any dift'erences, sulfur reduced fire-holding capacity niore on plots 

 not limed than on plots limed. 



The amount of sulfur wliich may be used on tobacco land infested with 

 Tliielavia depends on the initial pH value of the soil on the one hand, and on 

 the eff'ect of too much sulfur on burn on the other hand. On heavily limed 

 soil imder the conditions here described, loss caused by black root-rot was 

 reduced without injury to burn by one ajiplication of sulfur of 200 or 400 

 pounds per acre; but when these applications were repeated the following- 

 year, on the same plots, fire-holding capacity was impaired. 



SUMMARY 



Eft'ects of acids and of sulfur in lowering the pH values of soil and on 

 growth and black root-rot of tobacco are described. 



When the pH value of soil was lowered by the application of sulfuric or 

 nitric acids, infection by Thielavia was reduced accordingly. 



"When the pH value of soil was lowered, as from .5.9 to -5.0, by the ap- 

 plication of orthophosphoric acid (alone), black root-rot of tobacco was still 

 severe or even more severe. It is possible that salts of aluminum, instead of 

 or in addition to hydrogen-ion concentration, inhibit Thielavia basicola in 

 acid soils, and that orthophosphoric acid as well as lime inactivates such toxic 

 substances, \\ith consequent benefit to the fungus. An application of alumin- 

 um sulfate to the soil \\as found to reduce injury to toliacco caused by this 

 fungus. 



Soil pH values in field plots to which lime was last applied in 1923 were 

 still high enough in 1930, above 5.9, to be favorable to Thielavia hasicola. 



