ANNUAL REPORT, 1938 



11 



more than any other economic plant in this area, is extremely sensitive to the 

 influence of the preceding crop. Plants with a high lignin content, when grown 

 in rotation with tobacco, have a tendency to cause conditions favorable to brown 

 root-rot. It is not to be inferred, howe\ er, that the trouble may never arise when 

 tobacco has been grown continuoush- on a field, or that tobacco may never grow 

 normally when the preceding crop has been one likely to cause the trouble. These 

 exceptions arise at intervals, depending upon the conditions of the growing season. 

 The influence of the preceding crop on the crop yields and quality of tobacco this 

 year is illustrated by the following data. 



Preceding Crop 



Peppers 



Horseweed 



Seaweed 



Ragweed 



Gladiolus 



Squash 



Artichoke 



Carrots 



Redtop 



Turnips 



Buckwheat 



Cabbage 



Wheat 



Kentucky Bluegrass. 



Tomatoes 



Canada Bluegrass . . 



Sweet Clover 



Rye 



Millet 



Sudan Grass 



Alfalfa 



Red Clover 



Orchard Grass 



Sorghum 



♦Grade index, as used here, is a number expressing the grading quality of tobacco produced under 

 the conditions of the experiment. It is based upon the percentage yield of each grade of tobacco 

 and the relative values of these grades given below: 



Lights 1 .00 Long darks (19" and longer) 30 



Mediums 60 Dark stemming (17" and shorter) 20 



Long seconds (19" and longer) 60 Brokes 10 



Short seconds (17" and shorter) 30 Fillers 10 



The grade index is derived by multiplying the percentage of each grade of tobacco by the re- 

 spective rating of the grades, given above, and adding the products. 



Crop index, as used here, is a number expressing the crop value of tobacco produced under the 

 conditions of experiment. It is based upon the gross yields of tobacco in pounds per acre and the 

 grade index of the tobacco. Crop index is derived by multiplying the gross yield of tobacco in 

 pounds per acre by the grade index of the tobacco. 



Grade index and crop index and the adopted relative values of the different grades of tobacco, 

 as used here, do not necessarily represent current commercial prices of tobacco. 



The lignin is recorded not in total quantity left in the soil, but in terms of per- 

 centage found in the sample. For example, the total amount of lignin remaining 

 behind when gladiolus is removed is small, although the percentage found in 



