^O^^ MASS. EXPERIMENT STATION P.ULLETIN 229 



Similarly it is probable that a return of infested soil to a more acid Cvindi- 

 tion will not be immediately followed by a great reduction in the amoimt of 

 black root-rot. The results in 192.5 indicate thai the omission of lime and the 

 continuous culture of tobacco do not quickly result in the disappearance of 

 black root-rot injury. Further field work on this point is in })ronres&. 



Effect, of Lime on Yield of Tobacco in the Absence of Root-Rot 



It has been previously mentioned (p. 121) that certain investigators have 

 found that the yield of tobacco was increased by liming the soil, and one of 

 the objects of the work at the Massachusetts Agricultural Experiment Station 

 was to determine whether such was the case under our conditions and if so, 

 to measure the extent of increase. This was also a necessary preliminary to 

 drawing any conclusion as to the effect of liming on root-rot. No records of 

 yields for the first year of the experiment (1921) were made. The records of 

 the second year show an increase of 12 per cent on both the inoculated and 

 uninoculated parts of the field. Theoretically, this should have been larger 

 the first year, since root-rot must have taken a slight toll the second year. 

 During the third year the loss from root-rot more than counterbalanced the 

 gain from lime on the inoculated part, and there was a total loss of Ifi per 

 cent. Even on the uninoculated part, root-rot was beginning to reduce the 

 gain which would otherwise have been anticipated from liming, but there was 

 still a final gain of 7 per cent on this half. During the fourth year of the 

 experiment, root-rot had increased to such an extent that it more than over- 

 came the benefit of the lime on the uninoculated part, and we had a final 

 loss even on that side of 12 per cent as opposed to a 17 per cent loss on the 

 inoculated part. In 192.5 root-rot had increased so nuich that the benefit of 

 lime was overcome even more and tiie loss was about 35 per cent on both the 

 inoculated and uninoculated areas. This is a nuicli greater loss than could 

 have been predicted, since at the previous rate of progress the loss would 

 have been about 17 per cent. 



In answer to the first question which was proposed as the object of this 

 experiment we may state that the immediate effect of lime in this soil was to 

 increase the yield. In this case it was 12 per cent the second year. Undouiit- 

 edly, the degree of increase from liming depends on the reaction of the soil 

 before application is made. On a soil less acid tlian this, one would hardly 

 expect the same degree of increase. 



Hoza Acid Sliould the Soil Be? 



It has again been demonstrated that the ultimate effect of heavy applica- 

 tions of lime is to increase root- rot and thus reduce yield. The facts that (1) 

 neutral calcium salts such as land plaster do not produce this effect and (2) 

 other alkaline substances such as carbonate of potash do produce it, show that 

 the influencing factor is not the calcium but the alkaline character of the 

 lime. The less acid or neutral soil thus produced does not render the tobacco 

 plant more susceptible to attack but it favors the growth of the fungus and 

 results in a larger number of lesions on the root system. Although there are 

 probably no tobacco soils free from Thielavia, it is apparent that many of 

 them, by virtue of their acid reaction, are so nearly free that their infestation 

 is negligible; while others, by virtue of their less acid reaction, are so heavily 



