54 Journal of Agrictdtural Research voi. xvii, no. a 



the value of lime in the control of numerous plant parasites harbored in 

 the soil because the results obtained depend altogether upon the disease 

 concerned. Experiments in its use have been most complete in relation 

 to the control of potato-scab, clubroot of crucifers, and nematodes. 

 Limed soils favor scab, whereas clubroot and nematode injury are much 

 reduced by its use. 



With the appearance of a paper by Briggs (j), based on field experi- 

 ments in Connecticut, a great deal of interest was revived on the influ- 

 ence of soil reaction on plant diseases having their origin in the soil. 

 Briggs concluded briefly that materials applied to the soil which tended 

 to make it alkaline in reaction favored Thielavia-rootrot of tobacco, 

 whereas materials applied which made the soil acid reduced the disease. 

 The actual change in soil reaction apparently was not determined. On 

 the basis of these results the use of acid fertilizers came to be recom- 

 mended in both scientific and popular literature and the use of lime 

 cautioned against. Considerable experimental work also v/as under- 

 taken at various places with this and other diseases, some of which 

 apparently verified the results of Briggs, while others showed no favor- 

 able results. Thus, the problem has remained in a more or less uncer- 

 tain state. Clearly it is not one which is easily solved. Changing the 

 reaction of the soil from acidity to alkalinity, and especially from alka- 

 linity to acidity by the application of different chemicals, is open to 

 many difficulties not clearly analyzable. The problem of soil reaction 

 as influencing disease presents two aspects: First, to determine the actual 

 influence of the reaction of the soil medium upon the disease; and second, 

 to determine in how far this influence may be utilized in a practical 

 manner by actually changing the reaction of large areas of soil to a 

 sufficient degree to modify the severity of the disease. The latter prob- 

 lem is complicated by a number of factors, the most evident of which is 

 the naturally or normally attained reaction of the soil, since this must 

 have considerable bearing upon the amount of acid-producing materials 

 which must be applied to get the desired result. Aside from the final 

 influence of such treatment on the soil itself, in a system of economical 

 and permanent agriculture a more discouraging feature of the problem 

 is that from the standpoint of the disease, for, as will be shown, many 

 other factors must be taken into consideration, such as the suscepti- 

 bility of the variety of tobacco grown, the amount of infestation, and 

 the temperature of the soil. By varying these factors markedly differ- 

 ent results may be secured on the influence of soil reaction in relation to 

 disease. 



The experiments carried out in the investigation presented here v/ere 

 of two kinds, pot tests and field plot tests. The former were carried on 

 for the most part in the greenhouse during the winter season and the 

 latter on an old heavily infested tobacco field on the Station farm at 

 Madison. 



