ANNUAL REPORT, 1937 



11 



The Effect of Plants Grown in the Field on the Subsequent Tobacco Planted 

 in Rotation. (Walter S. Eisenmenger and Karol J. Kucinski.) It has been a 

 conjecture of the writers that there was a possible relationship between the 

 botanical species and rate of ammonification and nitrification of plant tissue and 

 the capacity to induce brown root-rot when different plants were grown in rota- 

 tion with tobacco. 



All the grasses tried with the exception of red top are conducive to the occur- 

 rence of the trouble. Red top decomposes the most slowly of all the grasses used 

 in rotation. 



The Solanaceae, potatoes, tomatoes, etc., do not seem to induce the trouble. 

 They decompose exceedingly rapidly to ammonia and nitrate nitrogen. Ragweed 

 and horseweed decompose fairly rapidly, and do not induce the malady. 



In 1936, the following varieties of plants were planted in a field, there being 

 4 plots of each: horseweed, alfalfa, Canada bluegrass, Kentucky bluegrass, sweet 

 clover, orchard grass, red clover, rye, wheat, artichoke, red top, ragweed, gladiolus, 

 turnip, tomato, pepper, cabbage, squash, sudan grass, sorghum, buckwheat, 

 carrots, millet, and seaweed (applied). The relative rate of ammonification and 

 nitrification of these plant tissues is known from previous experiments. 



This year tobacco was planted where these plants were grown in 1936. The 

 following table represents the yield and quality of the tobacco grown after these 

 different crops. 



Average Yield and Quality of Tobacco 



Pounds *Grade *Crop 



Preceding Crop per acre Index Index 



Tobacco 2125 .534 1135 



Horseweed 2099 . 495 1039 



Alfalfa 2049 . 499 1022 



Canada bluegrass 2093 .510 1067 



Kentucky bluegrass 2062 . 509 1050 



Sweet clover 2089 . 524 1095 



Orchard grass 2124 .500 1062 



Red clover 2051 .494 1013 



Rye 2097 .504 1057 



Wheat 2187 .506 1107 



Artichoke 2044 .510 1042 



Red top 2160 .525 1134 



Ragweed 2037 . 475 968 



Gladiolus 2034 .478 972 



Turnips 2006 .494 991 



Tomatoes 2143 .492 1054 



Peppers 2238 .477 1068 



Cabbage 2129 .508 1082 



Summer squash 2245 .491 1 102 



Sudan grass 1936 .487 943 



Sorghum 1853 . 474 878 



Buckwheat 2106 .499 1051 



Carrots 2127 .496 1055 



Seaweed 2643 .443 1171 



Millet 2143 .507 1082 



*The explanation of grade index and crop index will be found on page 21. The rel- 

 ative values used in 1937 are not identical with those used in previous years but are 

 very similar. 

 The plants of the grass family were variable in their effect on subsequent 

 tobacco > ields, while the legumes and Solanaceae were more consistent. The 



