6o Journal of Agricultural Research voi. xvir, No. a 



the same treatment as the others, the essential difference being that these 

 did not have the residual effects of the previous season's applications and 

 would therefore be more directly comparable with the plots in 191 7. 



The applications of lime were made on May 21 and fertilizers applied 

 on June 3. On June 12 all the plots were planted to Connecticut Havana 

 tobacco. On June 21 samples of soil were taken from each of the plots 

 and tested for reaction in the ordinary manner. 



In the infested soil the control plots showed very slight acidity. The 

 acid plot of last year (full amount) showed medium to strong acidity; 

 the half-amount plot showed slight acidity. In the same way the plots 

 which had received the acid fertilization for the first time in 191 8 showed 

 nearly medium acidity for the full application and slight acidity for the 

 half amount. None of the alkaline plots showed acidity and presumably 

 were considerably below the neutral point, though this could not be 

 shown by the test used. On the uninfested plots the change in acidity 

 due to the application of the fertilizers were not so marked, probably only 

 a slight change having been produced. The limed plots, however, 

 showed no signs of acid reaction. 



On June 18 it already appeared that on the full-limed plots the lime 

 was acting injuriously upon the seedlings, both in the uninfested and in 

 the infested soils. This may have been due in part to the fact that the 

 lime was not well air slaked and was, hence, not thoroughly incorporated 

 in the soil. The action of the lime was, therefore, probably toxic and 

 probably vitiated the results, so far as lime was concerned, although the 

 plants appeared to recover later in the season. The outstanding feature 

 of the results in 191 8 was again that the plots made acid with heavy 

 applications of fertilizers under field conditions were on the average little 

 or no better than the untreated plots (Table IV) . In fact, the untreated 

 plots of the 191 7 series were considerably better than the acid-treated 

 plots of 1917 or 1918, although the plots treated with acid fertilizers for 

 the first time in 191 8 were slightly better than their controls for this year. 

 There is no question as to the extent of infection on this soil this season, 

 since resistant and susceptible types planted at the same time behaved 

 in the expected manner. In interpreting the results from the field plots 

 it should be recognized that the tests are not exhaustive, and that on 

 account of the complexity of the problem the conclusions drawn may not 

 apply under all conditions. For Wisconsin conditions, however, it ap- 

 pears that the application of acid fertilizers to soils, alkaline or neutral in 

 reaction, will not reduce infection by T. hasicola. 



SOIL TEMPERATURE AS A FACTOR IN ROOTROT 



A review of the more important literature concerning the influence of 

 soil temperature on diseases of plants and the importance of such studies 

 has been presented by Jones (16). With respect to the influence of 

 this factor on infection and severity of the rootrot of tobacco caused by 



