THE BROWN ROOT EOT OF TOBACCO AND OTHER PLANTS 



15 



In greenhouse and in field experiments, the application of commer- 

 cial fertilizers to brown root-rot soils has frequently resulted in marked 

 increases in yield, but these apparently contradictory results may be 

 explained on the basis of environmental conditions. They are sig- 

 nificant only in that they seem definitely to overthrow the hypothesis 

 sometimes suggested that brown root rot is a consequence of over- 

 fertilization of the soil. In a practical sense, however, it is to be 

 regarded as poor practice to attempt to bring about good yields in 

 brown root-rot fields by the application of fertilizers. This conclusion 

 may be illustrated by the results obtained on the heavily fertilized 

 experimental plats at Whately, Mass., in 1922, where the yield of 

 tobacco ran as low as 460 pounds per acre as compared with a yield 

 of more than 100 bushels of corn. (See Table 2, p. 21.) 



Fig. 13. — A field of tobacco at Whately, Mass., badly affected with brown root rot. 

 The bagged plant was selected for resistance to disease, but later this plant, along 

 with others, proved to be of no value 



The tobacco soils of the Connecticut Valley are on the whole more 

 or less acid in reaction. A considerable number of determinations 

 have been made in connection with this work, both by the Truog 

 method and the colorimetric method for H-ions. These determina- 

 tions have been made largely on diseased soils, but normal soils have 

 been used for comparison. The conclusion is justified from these 

 results that the acid reaction of the soil bears little, if any, relation 

 to brown root rot. In experiments planned to determine the influ- 

 ence of liming soils on the growth of tobacco, there is some indica- 

 tion that lime is slightly detrimental rather than beneficial on brown 

 root-rot soil, although lime may be somewhat beneficial to soils free 

 from disease. 



