58 Journal of Agricultural Research voi. xvii, no. 1 



FIELD EXPERIMENTS WITH SOIL REACTION 



The field plots were located on the Experiment Station farm at Madison 

 on a tobacco field which had grown 10 and possibly 12 successive crops 

 of tobacco, and on a neighboring field which had previously grown only 

 I crop of tobacco. The infested field had for three or four years previous 

 to this experiment shown itself to be heavily infested and would grow 

 only half a crop of Coimecticut Havana tobacco, while White Burley 

 would make no growth whatever on this soil, especially during relatively 

 cool growing seasons. This soil had had heavy annual applications of 

 barnyard manure and was in a good state of fertility as shown by corn 

 and cereals growing in adjacent plots. The soil reaction at the beginning 

 of the experiments was practically neutral. 



A control field across the road on uninfested soil was started for a 

 double purpose. In the first place it made it possible to check up the 

 beneficial or injurious action of the fertilizer and lime applied, aside from 

 infection from disease. In the second place it has been considered that, 

 although the apphcation of acid fertilizer might not remedy the condition 

 in a badly infested field, it might serve to hold down the rate of infesta- 

 tion of new soil to a considerable degree. This soil is equally as fertile 

 as the infested field, but shows a slightly greater degree of natural acidity, 

 being classed as slightly acid according to the Truog color chart. Since 

 it was found in the pot experiments that a very considerable range of 

 reaction was required to make any appreciable difference in amount of 

 infection by T. hasicola, it was decided to use the more simple though 

 fairly accurate comparative test of Truog {26) with lead-acetate paper. 

 The reference to the degree of acidity, therefore, will be based on the 

 standard color chart accompanying the description of this test. 



The plots used were one-fortieth acre in size. The applications were 

 made in two different amounts, a heavy application and a light applica- 

 tion, also referred to as a full application and a half application, respec- 

 tively. The original plans of the experiment called for the use of alkaline 

 fertilizers — that is, potassium carbonate, basic slag, and nitrate of soda, 

 with equivalent amounts of sulphate of potash, acid phosphate, and sul- 

 phate of ammonia for the acid fertilizers. On account of the apparent 

 impossibility of obtaining all of the alkaline fertilizers, it was decided 

 to use the acid fertilizers and heavy applications of lime to produce the 

 alkaline condition. The rates of applications, in pounds per acre, then, 

 are as follows: 



Acid plots. Full amount. Half amount. 



Sulphate of ammonia i, 200 600 



Sulphate of potash i, 200 600 



Acid phosphate 2, 400 i, 200 



Alkaline plots. 



Slaked lime 12, 000 6, 000 



Sulphate of ammonia i, 200 600 



Sulphate of potash i, 200 600 



Acid phosphate 2, 400 i, 200 



