120 



MASS. EXPERIMENT STATION BULLETIN 229 



calcium hydroxide to a naturally very acid soil inoculated with macerated 

 diseased roots. Acidity was determined in terms of lime requirement accord 

 inji' to the Truoj>' method. From these experitnents they concluded that: 



" . . . . the iiigiiest acidity practically eliminated damage from root-rot, 

 but that heavy infection still occurred in fairly acid soil." 



When they inoculated all the soils heavily with spores of tlie fungus jnsf 

 before plantincj, they found that: 



"A heavy infestation apparently reduced tiie efficacy of the acid soils to 

 nothing, at least in the presence of a susceptible variety. The disease ap- 

 peared, in fact, more virulent in the most acid soil." 



This last experiment indicates that the effect of the acid soil is not to 

 increase the resistance of the plant but to retard tlie development of the 

 fungus. 



They also tested in the field the effect of a{>plication of acid fertilizers and 

 concluded that: 



"For Wisconsin conditions .... application of acid fertilizers to soil, alka- 

 line or neutral in reaction, will not reduce infection by T. batticola." 



Chapman (2) in connection with an investigation of "tobacco sick" soils of 

 Massachusetts made 300 determinations of tiie lime requirement of tobacco 

 soils and correlated them roughly with the condition of the crop and pre- 

 valence of root-rot. He concludes (2:38) that: 



"Soils with a lime requirement up to 3000 pounds CaO per acre are not 

 producing good crops as a rule and are comparatively free fn^ii r(X)t-rots. 

 Those with a lime requirement of from 3000 to 8000 pounds CaO per acre 

 are in good tobacco condition; but in this group, patiiogenic fungi are abimd- 

 ant in the soil, and the plants during certain seasons, are very liable to suffer 

 from root-rots caused by some of these fungi. Soils with a lime requirement 

 of 8000 pounds CaO up are usually comparatively free from such fungi, and 

 even in unfavoralile seasons, little disease is found." 



He explains the relative freedom from root-rot of the soils whicii show tlie 

 lowest lime requirement by assuming tliat these soils are too alkaline for the 

 development of the fungus. His results on this point are at variance with 

 those of Johnson and Hartman. The poor yield is attributed to the unfavor- 

 able effect of a too alkaline soil on the tobacco plant. 



Chapman questioned t!ie lime refpiiremenl nsothod as a means of measuring 

 the acidity of the soils. 



Need of Fuutheb Investigation 



We may sununarize the results of all th.e investigations recorded up to the 

 present: A soil made less acid by the use of lime, carbonate of potash, or 

 ashes favors the development of black root-rot. When, however, the acidity 

 is increased, there is a corresponding reduction in amoimt of root-rot injury 

 luitil a point is reached where it is negligible. In regard to the particular 

 degree of acidity which must be attained to escape root-rot and, in general, 

 the correlation of reaction and infection throughout the soil range, Briggs 

 gives no information while Johnson and Hartman and Chapman had contra- 

 dictory results. In view of this situation and the fact that it is now commonly 

 accepted that the development of fungi is proj)ortionate to infensiti/ of acid- 

 ity as measured by the lij'drogen ion concentration method, rather than the 

 amount of acidity, as measured l)y the lime requirement method, there seemed 

 to be need for further experimentation. 



