lU.ACK ROOT-KOT OF TOBACCO 133 



of sulfur to .1 relatively acid soil did not interfere with the growth of tohac- 

 eo. Sulfur did, however, inerease yields more on limed plots with l)hick root- 

 rot consecjuently a factor than on plots not limed. 



On the basis of yields in 1927, the oi)tiniuni rate of application of sulfur 

 for this soil was nearer KM) than SOO pounds per acre. Yields of tobacco on 

 limed plots were increased more in 1927 by sulfur, 400 pounds per acre, ap- 

 plied in 1926 than by sulfur, KH) pounds per acre, applied in 192() and again 

 in 1927, or a total of 800 jtounds. 



In 1928, for the tirst and only time, yields were larger on limed plots 

 tlian on ]ilots not limed. (Talile 1'3.) In this abnormally rainy season, the 

 etfects of sulfur on yields of i)lots not limed were inconsistent; there were 

 increased yields on some of the plots, following some of the treatments, but 

 on duplicate plots yields were lower than on the check plot without sulfur. 

 Yields on limed plots in 1928 were not consistently increased by sulfur. On 

 the lower part of the field growth was very poor regardless of all factors 

 except too much water in the soil. The yields in 1928 on limed plots to which 

 sulfuric and orthophosphoric acids were applied in 192t) were 21 and 19 per 

 cent greater than those of their checks, jdots 12 and 21 respectively, limed 

 but not acidified. 



Yields of tobacco in 1929 (Table 11) on limed plots acidilied were 

 greater, as in earlier years, than were yields of tobacco on limed plots not 

 acidified. The acidification treatments of limed plots which were most effective 

 in increasing yields were sulfur, 200 pounds per acre applied in 1926 and 

 1927, and sulfuric and orthophosphoric acids applied two years. The other 

 acidification treatments resulted in increases of from 8 to 14 per cent on 

 limed plots. Acidification treatments of limed plots did not increase yields 

 as much in 1929 as they did in 1926 and 1927. The application of sulfur to 

 plots not limed, and with black root-rot consetjuently not a factor, did not 

 significantly or consistently affect yields in 1929. 



In 1930 the yields of tobacco on limed plots were increased 16, 17, or 18 

 per cent by sulfur, tOO pounds per acre applied in 1926, the same applied in 

 1926 and 1927, or the acids applied in 1926 and 1927. (Table 15.) These in- 

 creases were about the same as those resulting in 1929 from the same treat- 

 ments; but as in 1929, the increases were much less than in 1926 and 1927, 

 the years of or immediately following the application of the acidifying treat- 

 ments. In 1930, as in most cases in the earlier years, yields of tobacco on 

 plots not limed were not materially affected by sulfur. 



Sulfur (not inoculated) was applied in 1930 to the soil of another field 

 here designated as Field Y, at the rate of 600 pounds per acre. The applica- 

 tion was made in April, at which time the pH value of this soil was 7.0. The 

 effects of this application on the pH value of the soil are shown in Table 7. 



The pH values of the soil in the plots which received sulfur were lower 

 than those of their checks by 0.2 to 0.6 on July 16. The pH value of this 

 soil was so high in the beginning, however, that although the pH value was 

 lowered as much as to 6.1, it was not enough to prevent black root-rot, and 

 yields of tobacco were unaft'ected. 



In these experiments, then, the application of sulfur to soil increased 

 yields of tobacco nuirkedly and consistently when the soil was infested with 

 Thielavia and when the pH value of the soil was lowered by the sulfur to 

 below 5.9, but not under other conditions. 



