BLACK ROOT-HOT OF TOBACCO 137 



Loss in yield of tobacco, caused directly by black root-rot and indirectly 

 by lime, reached its maximum (about 44 per cent) in 1925 and 1926, the 

 second and third years after lime was last applied. In subsequent years, this 

 loss in yield on limed plots (in all cases as compared with yields on plots not 

 limed) decreased so that it was about 24 per cent in 1929 and 1930. 



Lowered yields on limed plots were usually associated with poorer quality. 



In four out of six years, lime did not increase the fire-holding capacity 



of the leaf, as determined in strip tests. Abundant rainfall was associated 



with improved burn and had more eft'ect than did lime on the length of time 



leaves held fire. 



Tobacco and alfalfa were equally efficient, and much more efficient than 

 timothy, in removing calcium and magnesium oxides from limed soil; but witli 

 no sulfur or acids applied, none of these crops caused a lowering of the pH 

 value of the soil between 1926 and 1930. 



Thielavla basicola did not infect alfalfa grown in limed soil infested with 

 this fungus. As far as black root-rot is concerned, there is probably no rea- 

 son why alfalfa cannot be grown in a rotation preceding tobacco. 



The substitution of a hay crop for tobacco on over-limed, Thielavia-in- 

 fested soil is not to be recommended as a means of overcoming black root-rot 

 of later crops of tobacco. 



Following timothy, brown root-rot of tobacco was equally severe on plots 

 limed and on plots not limed. 



Alfalfa or alsike clover as a cause of brown root-rot of tobacco was much 

 less injurious than was timothy. In the second year of tobacco following al- 

 falfa on limed soil infested with Thielavia basicola, there were marked in- 

 creases in yields of tobacco as compared with yields of tobacco on plots on 

 which tobacco was grown every year; but in 1930 tobacco following alfalfa 

 (last grown in 1927 or 1928) yielded no more than did continuous tobacco. 



The pH value of soil was lowered as much, or more, the year sulfur or 

 acids were applied as in the years following. Soil pH values were lowered for 

 four years by sulfur, 400 pounds per acre, but sulfur, 200 pounds per acre, 

 was not enough in this soil to keep the pH value low. 



The severity of black root-rot was lessened by all acidification treatments 

 in the year of their application. Sulfur, 400 pounds per acre applied two 

 years in succession, lessened the severity of black root-rot in these and the 

 three following years. 



Yields of tobacco on limed plots infested with Thielavia basicola were 

 increased^ by all acidification treatments the first year the materials were ap- 

 plied. The application of sulfur to plots not limed, and on which there Mas 

 no black root-rot, either increased yields of tobacco somewhat or did not 

 affect them. Sulfur applied to limed plots increased yields more in the year 

 following than in the year of its application. The optimum rate of applica- 

 tion of sulfur to this soil, as evidenced by yields of tobacco as well as effect 

 on burn, was nearer 400 than 800 pounds per acre. Increased yields from 

 some of the acidification treatments have continued up to the present (1930). 

 Increased yields associated with acidification treatments of limed plots 

 were accompanied in general by increased percentages of leaves of the grades 

 lights, mediums, and seconds (as contrasted with darks and fillers). 



The application of sulfur, 400 pounds per acre in one year, to limed plots 

 reduced the fire-holding capacity of the tobacco in the year in which it was 

 applied but not in the three years following. This is considered to be the 

 maximum application which is safe on this soil. 



