128 MASS. EXPERIMENT STATION BULLETIN 276 



of tobacco on limed plots on which tiniothj^ Mas grown in 1927 and 1928 were 

 17 and 37 per cent less than yields on plots cropped continuously with to- 

 bacco. Two years of timothy were, therefore, much more injurious than were 

 two years of alfalfa. However, the yield of tobacco the second year after 

 timothy, last gro\\n in 1927, was as good as on plots where tobacco followed 

 tobacco. There was, however, no really increased yield of tobacco on limed 

 plots resulting from the substitution of timothy for tobacco in previous years. 

 In 1930 tobacco on limed plots following timothy yielded as well as (in fact 

 a little better than) tobacco on plots on which only tobacco was grown in 

 earlier years. 



Alsike clover was confined to plots not limed, and its effect on the tobacco 

 which followed it may, therefore, be compared only with that of timothy. It 

 was nnich less injurious than was timothy. Timothy was associated with a 

 loss in yield of tobacco of 81 or 69 per cent in 1928, while the loss in yield of 

 tobacco following alsike clover was 45 or 49 per cent (in duplicate plots). 



The substitution of these hay crops for tobacco on limed and Thielavia- 

 infested soils is not to be recommended as a means of increasing soil acidity 

 or overcoming black root-rot in later crops of tobacco. 



Effects of Sulfur and of Acids in the Field 



On pH Values of Soil 



The effects of the several acidification treatments on pH values of soil in 

 limed plots from 1926 to 1930, inclusive, are recorded in Tables 11 to 15. The 

 actual pH values which resulted from each of the several treatments are 

 significant only in connection with this one soil; for as indicated by results in 

 another field described below, and as pointed out by other investigators (23, 

 21), sulfur (or sulfuric acid) may not give the same results in soils of differ- 

 ent types. However, the relatively small changes in pH value of soil which 

 resulted from the application of sulfur or the acids to limed plots were ac- 

 companied by materially increased yields of tobacco and less black root-rot. 



The pH values of the soil in limed plots to which the acidifying chemicals 

 were applied only in 1926, one month before tobacco plants were set, were as 

 low in that year (pH 5.6 to 5.8) as in the following years; that is, these treat- 

 ments did not lower the pH value of the soil increasingly after the first year. 

 This is as would be expected, for in experiments by other investigators (26, 

 15, 30), 80 per cent or more of the sulfur applied fo soil was oxidized within 

 a month or during the growing season; and McKibben (23) observed that the 

 acid effect of sulfur applied to soil reached its inaxinumi within two or three 

 months. 



The applicaton of sulfuric and orthophosphoric acids in 1926 resulted fn 

 sufficiently lowered pH values of the soil (to about 5.7) in 1926 and 1927 but 

 not in 1928 or 1929. The application of these acids in two successive years, 

 1926 and 1927, resulted in lowered pH values (to 5.6 or 5.7) in every year 

 through 1930. Nine weeks after this treatment was applied in 1927, the pH 

 value of the soil Mas lowered 0.2 or 0.3 by it. 



.Sulfur, 400 pounds per acre, applied in 1926 lowered the soil pll values 

 to 6.7 from 5.9 in 1926 and 1927, and it had less but some effect in 1928, 1929 

 and 1930. The application of 400 pounds of sulfur in 1926 and again in 1927 

 resulted in lowering the pH values of the soil in 1927, 1928, 1929, and 1930. 



Sulfur, 200 pounds per acre, applied in 1926 or in 1926 and 1927 was less 



