May IS. 1919 Influence of Soil Environmeyit on Rootrot of Tobacco 



TabliJ VII. — Average monthly and seasonal soil temperatures for tobacco-growing periods, 

 IQIS-IQ18, at different depths of soil 



Season. 



1915- 



1916. 



1917. 



1918. 



Average 



for 

 growing 

 period. 



C. 



20.3 

 20. o 

 18.5 



27.7 



24- 5 

 21.8 



25.8 

 22. 7 

 19.8 



26.6 

 23.0 



The practical bearing of this problem is manifold. In so far as sea- 

 sonal temperatures can be judged and predicted, crop prospects on in- 

 fested soils can be predicted, and in the northern tobacco-growing sec- 

 tions the infested soils usually constitute anywhere from one-half to 

 three-fourths of the acreage grown. In so far as "warm" soils can be 

 selected — that is, sandy, dark soils with good drainage and a southerly 

 exposure — in preference to "cold" soils, the possible extent of the damage 

 from disease has been reduced. If the crop is planted early on infested 

 soils, heavy infection is more Ukely to occur in the early stages of plant 

 growth, and the plants will find it more difficult to recover. One of the 

 most common beliefs of the Wisconsin grower, based on observations 

 of several years, is that early planting means plants budding out 

 in July, and an early, light-weight crop. From a purely physiological 

 standpoint there could be only one possible explanation for such behavior 

 of early-set tobacco, namely, the more or less common occurrence of a 

 drouth in July. The inadequacy of such an explanation, however, is 

 shown by the follomng observations: The vigor of growth of corn and 

 other cultivated crops has remained practically unchecked during many 

 of these frequently recurring so-called drouths in July; likewise, the 

 growth of ordinary tobacco on new soil of a neighboring farm or of a 

 resistant variety in the adjoining row on an infested field has not been 

 greatly interfered with by these weather conditions; finally, exceptionally 

 poor crops of tobacco were grown in Dane County, Wis., in the years 

 1 91 3 and 1 91 5, whereas the July rainfall was 8.47 inches in 191 3 and 5.04 

 inches in 191 5, both greatly in excess of the normal. 



It would seem that some value could be attached to late planting on 

 soil infested by T. hasicola, in view of the low temperatures in June. 



