BLACK KOOT-KOT OF TOBACCO 123 



of tobaccHt) from each plot were determined/ Roots of tobacco plants were 

 examined for black root-rot and brown root-rot at the time the tobacco was 

 cut. 



The pH value of the soil, the yields per acre of cured leaf, the results of 

 the sorting, burn tests, and root examinations are recorded for each plot 

 and each year so far as they are available, in Tables 11-15 in the appendix. 



Effects of Lime 



'J** pH values of Soil and on Yields of Tobacco. 



The pH values of the soil in limed plots 12 and 24 may be compared with 

 the pH values of soil in unliiTied plots 5, 17, 6, and 18 by reference to Tables 

 11-15, for the years 10-26, 1927, 1928, 1929, and 1930. None of these plots re- 

 ceived sulfur or acids. 



The pH value of limed soil did not change more than 0.2 from 1926 to 

 1930 inclusive, and that change was from about 5.9 to 6.1, or not in the di- 

 rection of increased acidity. Soil pH values in limed plots were still favorable 

 to Thielavia basicoht in 1930, seven years after the application of lime. The 

 soil in plots not limed had meanwhile become increasingly acid, the pH values 

 changing from about 5.4 in 1926 to about 5.0 in 1930. 



In Table 3 the yields of tobacco on plots not limed are compared with 

 the yields on the limed jilots, and the losses in yield on limed plots, exjiressed 

 as percentages of yields on plots not limed, are recorded. Tobacco was grown 

 every year on all of these plots and to none of them were acidifying chemicals 

 applied. 



Table 3. — Effects of lime (applied last ix 1923) ox yields of tobacco 

 FROM 1925 to 1930, ixclusive. 



Year Yields per acrf' 



Unlimed plots 1 



Ponnds 



1924 1-548 



1925 1230 



1926 1648 



1927 1536 



1928 789 



1929 1519 



1930 1924 

 * Means for (hiplicate plots. 



The loss caused directly by black root-rot (as evidenced by root examina- 

 tions) on plots last limed in 1923, reached its maximum (45 or 43 per cent) 

 in 1925 and 1926, and was considerably less in 1927. 



In 1928 the total precipitation in June, July, and August Mas 74 per cent 

 more than the normal for this period. As Chapman (12) has pointed out, ex- 

 cessive summer rainfall in Massachusetts is always followed by a reduction 

 in the yield of tobacco. Furthermore, the soil in this field is not very well 



■* By Philip H. Smith and Henri D. Haskins of Massachusetts Agricultural Exper- 

 iment Station. 



