226 MASS. EXPERIMENT STATION BULLETIN 229 



Season of 1925 



The effect of lime on l)Iadv root-rol and yield and the effect of tiinotliy cover 

 crop on yield were ne\er more conspicuous than in 1925, although no cover 

 crops had been planted and no lime applied since 1923. 



Throughout the season growth was much superior in vuilimed plots to 

 growth in limed plots. It was apparent that on plots which had had a cover 

 crop of timothy in previous years the tobacco was making a better growth 

 than on plots which had never had a cover crop of timothy. In other words, 

 the depressing effect of timothy which had been observed in previous years 

 was not in evidence after this cover crop was omitted for one year. There 

 was no visible difference in growth between the inoculated and uninoculated 

 halves of the field. It was evident that, regardless of inoculation, black root- 

 rot was causing loss in all limed plots. 



When the roots from all plots were examined at harvest time, an average of 

 98 per cent of the plants in all limed plots was found to be severely infected 

 with black root-rot. In unlimed plots an average of only 14 per cent of the 

 plants showed symptoms of this disease, and infection on them was slight. The 

 previous cover crop was found not to aff'ect the amount or severity of black 

 root-rot. Infection, as revealed by the examination of the roots, was the same 

 on the inoculated and uninoculated parts of the field. Brown root-rot was 

 slightly more pronounced on limed than on unlimed plots, but the ditl'erence 

 was small. 



The soil in limed plots bad, in April 1925, pH values from 6.4 to 7.0. In 

 all these, plants were severely infected and there were no visible differences 

 between them as regards infection. The soil in unlimed plots ranged in pH 

 values from 4.5 to 5.0. Infection in these plots was absent or slight, and there 

 were no appreciable differences between them. 



In 1925 the yield on inoculated plots was no less than the yield on plots 

 not inoculated. 'I'he black root-rot fungus was evidently present in all plots, 

 but had not become established in unlimed plots because of unfavoral)le soil 

 conditions. It had, however, become established in limed but iminocnlated 

 plots. The black root-rot fungus is probal)ly prescilt in all tobacco soils, 

 but it is evident that it causes no loss in soils having a reaction unfavorable 

 to the fungus. 



The average reduction in yield due to liming ("35 per cent) was greater in 

 1925 than in any previous year of the experiment, although no lime was ap- 

 plied in either 1924 or 1925. During this two-year period without more lime 

 added, the soil in the limed strips had, however, become slightly less acid. 

 The omission of lime for two years on land on which tobacco was grown con- 

 tinuously did not result in any immediate relief from black root-rot. The 

 greater loss in 1925 was probably not directly due to any change in the soil 

 ifaction, but to the fact that the soil is becoming more completely infested 

 with the funirus. 



The injurious action of lime as expressed in black root-rot was not more 

 pronounced in its effect on yield than on quality and value. This is recorded 

 in Table III under per cent darks, seconds, mediums, fillers, and brokes. The 

 average per cent mediums and seconds on limed plots was 6, and on unlimed 

 plots 22. The average per cent fillers on limed plots was 39 and on unlimed 

 plots 17. 



In 1924, for the third consecutive year, the use of timothy cover crop was 

 associated with a reduction in yield. No cover crop was sown in 1924. In 



