May 15. 1919 Influence of Soil Environment on Rootrof of Tobacco 79 



This fertilizer was added to each pot in each series and thoroughly mixed 

 with the soil in the amounts shown in Table X; the application ranged 

 from one which was considered only light, to one which was so heavy as 

 to decrease materially the yield. In these pots three successive crops 

 were grown; the first being the susceptible White Burley;the second the 

 semi- resistant Connecticut Havana; and the third the susceptible Mary- 

 land Broadleaf variety. The average air-dry weights for the plants in the 

 infested and the uninfested soil for the three crops are given in Table X: 



Table X. — Influence of fertilizer on roof rot of tobacco 



Series. 



Fertilizer 

 added. 



Gm. 



3-5 



7.0 



14. o 



20. o 



56.0 



Average air-dry weight (gm.) per plant. 



First crop (White 

 Burley). 



Uninfest- 

 ed soil. 



Infested 

 soil. 



0-95 

 2. 25 



•57 

 • 17 



Second crop (Con- 

 necticut Havana). 



Uninfest- 

 ed soil. 



7-97 

 12. 05 



11-75 



12. 17 



II. 00 



6. 10 



Infested 

 soil. 



4. 62 



3-87 

 3.60 



3-75 

 1.50 



•59 



Third crop (Mary- 

 land Broadleaf). 



Uninfest 

 ed soil. 



5.60 

 5-25 

 5-85 

 9.40 

 16.80 

 6. 42 



Infested 

 soil. 



O. 52 

 60 



45 

 40 



31 

 15 



It may be observed at once that the uninfested soil responded to the 

 fertilizer treatment; the maximum yield for the first and second crops 

 was in the pots which received 14 gm. of fertilizer. Doubling the amount 

 of salt, however, decreased the yield, and quadrupling it acted ver>' 

 injuriously, presumably owing to increased concentration of the soil 

 solution. Very poor growth was made on the infested soil in all cases 

 (PI. 5, II-III). In the first experiment, though, the lowest application 

 of fertilizer apparently increased the growth, followed, however, by a 

 decrease at higher applications. The most striking fact was that the 

 most beneficial application on the uninfested soil showed no signs of 

 such beneficial action on the infested soil. 



The results obtained with a more resistant variety as a second crop 

 are believed to be more representative. In this case there is a gradual 

 decrease in yield with the application of the nutrient salts on infested 

 soil; no increase from the application of 3.5 gm. of fertilizer occurred as 

 in the first crop grown. This influence of a light application of fertilizer 

 to infested soils is apparently in need of further investigation on a wide 

 range of soils and with different vaiieties. From a practical standpoint 

 it seems safe to conclude that fertilizer as such is wasted when applied 

 for tobacco on soils badly infested with T. basicola, and that it may, in 

 fact, do more harm than good. 



