ANNUAL REPORT, 1929 337 



were about the same but somewhat lower than after corn and hay. This 

 is an unusual result because in previous years better yields have been 

 obtained after onions and potatoes than after corn and hay. 



In 1929 brown root-rot affected the roots of the tobacco but slightly 

 on the cover and no-cover crop plots but did injure the roots of the to- 

 bacco in rotation with corn and hay very severely and to a less extent 

 that in rotation with potatoes and onions. 



In the greenhouse, with water cultures, aluminum has been found to 

 ])roduce an effect on tobacco roots similar to that of brown root-rot in 

 the field. Thinking that aluminum in the soil might be a factor in caus- 

 ing brown root-rot in the field, treatments were made on the rotation 

 plots to eliminate any effect of soluble aluminum. These treatments 

 consisted of large applications of superphosphate, which experiments at 

 other stations have proven to be successful in counteracting the injurious 

 effects of aluminum. The results were not particularly encouraging. 

 Brown root-rot was just as severe where the superphosphate treatments 

 were made as where they were not. The yield was not increased by the 

 superphosphate, which is contrary to experience with similar treatments 

 on other plots in the absence of brown root-rot. It might be said from 

 this year's experience, if it can be assumed that superphosphate renders 

 soluble aluminum inactive, that the brown root-rot found in the field is 

 not caused by an excess of soluble aluminum, and that it is a different 

 type from that observed in the greenhouse water cultures as resulting 

 from aluminum injury. 



Soil nitrate determinations were made during the growing season of 

 1929 to see whether plowing under carbonaceous residues had reduced the 

 available nitrogen, as found by other experiment stations. The data ob- 

 tained are in agreement with those of previous years in showing no case 

 where the residues turned under in the rotations have reduced the avail- 

 able nitrogen to the point where it limited the growth of tobacco. 



Quantity of Nitrogen and Phosphorus for Tobacco. (J. P. Jones and 

 M. E. Snell). The phase of this experiment dealing with the amount of 

 nitrogen required in growing tobacco was started in 1926. The recom- 

 mendations which seem justified from work on the experimental plots to 

 date are: (1) In the absence of barnyard manure, 150 pounds of ammonia 

 per acre is the minimum that should be considered in fertilizing tobacco; 

 (2) a somewhat better yield has been obtained each year with 200 pounds 

 of ammonia per acre than with 150 pounds, and for many fields the larger 

 application may be nearer the optimum; (3) although in previous years 

 250 pounds of ammonia per acre produced slightly superior yields, in 

 1929 it gave no better yields than the 200-pound treatment; and it has 

 been concluded that this large application will prove profitable only in 

 unusual situations. 



Among the observations made on tobacco, it Mas noted that the re- 

 duction in growth due to the deficient nitrogen was always apparent 

 before the typical yellow color signifying nitrogen starvation. In 1928, a 

 rainy season, the yellow color was found much earlier than in 1929, 

 a dry season. Although reduced growth could be seen readily on the 

 low nitrogen plots in 1929, yellowing of the leaves was scarcely per- 

 ceptible even at the time of harvest. 



