2 BULLETIN 765, U. S. DEPARTMENT OF AGRICULTURE. 



which will be briefly considered at this time. In the Connecticut 

 Valley tobacco growers have less area to exploit, and although the 

 land is not naturally fertile heavy applications of commercial fer- 

 tilizers are used with profit. Under the conditions there experience 

 has shown that it is possible to grow tobacco commercially with more 

 or less success by the continuous-culture system. In the Burley dis- 

 trict there is as a rule no dearth of tobacco land and the soil is natu- 

 rally quite fertile, so that practically no commercial fertilizers are 

 used. Here experience has shown that tobacco can not be success- 

 fully grown on the same soil for more than two years in succession, 

 although other crops following tobacco willgrow very satisfactorily. 

 Briefly, the accepted explanation for half a century has been that to- 

 bacco is very hard on the soil, in that it removes great quantities of 

 plant food, and some growers have thought that the supply of cer- 

 tain kinds of this food which are essential for tobacco but not for 

 other crops becomes exhausted, at least temporarily. In Connecticut, 

 then, enormous applications of fertilizer have been resorted to in 

 order to maintain production, while in the Burley district the soil 

 which has grown tobacco for one or two years is given a 5 to 10 year 

 " rest," usually in sod, to remedy the condition of " exhaustion." 



The purpose of this bulletin is to show the incorrectness of the 

 commonly accepted explanations, especially as applied to the Burley 

 section. The cigar-tobacco sections have made equally incorrect in- 

 terpretations of the special requirements of the tobacco crop, and the 

 attempt has been made to maintain production by heavy applications 

 of fertilizer rather than by crop rotation. Owing to the variety of 

 tobacco grown, it will be shown that the Burley grower is at once 

 forced to change his land, whereas, on the other hand, the cigar- 

 tobacco grower, using other varieties, has been able to keep up con- 

 tinuous cropping with considerable success. It is now known that 

 there is a root disease which has been an important factor in deter- 

 mining cropping methods used in tobacco culture. 



DESCRIPTION OF ROOT-ROT. 



In some sections many tobacco growers have become more or less 

 acquainted with the disease of tobacco known as root-rot and realize 

 its importance as related to crop production. Unfortunately, how- 

 ever, a great many growers are entirely unaware of the occurrence of 

 the disease, even though it be the cause of a total failure of the 

 tobacco crop on their soils. The primary reason for this is at once 

 evident. Though growers as a. rule are very keen in observing small 

 diseased areas on the stems and leaves of plants, they rarely exam- 

 ine with care the roots, which are hidden in the soil. Many growers 

 gain their first acquaintance with the root-rot while pulling plants 

 from the seed beds. In some districts most tobacco growers, per- 



