NITROGENOUS FERTILIZERS FOR TOBACCO 5 



According to experiments conducted at the Connecticut Experiment Station 

 (9), an average crop of Havana Seed tobacco, comparable in yield and grading 

 quality to those grown in the present experiment, removes from the soil 114 

 pounds of nitrogen. This is the total amount removed by the entire plant — 

 leaves, stalk, and roots. The question then naturally arises as to why it is 

 necessary to apply as much as 164.7 pounds of fertilizer nitrogen in order to 

 get an optimum crop. Besides the nitrogen applied in the fertilizer, the soil 

 contains several hundred pounds of organic nitrogen per acre, part of which 

 becomes available during the growing season through the process of nitrifica- 

 tion. In this experiment a cover crop of oats was sown each year following 

 the harvest of the tobacco crop. 



Nitrates were determined in soil samples taken from the plots receiving the 

 different quantities of nitrogen. The average concentration of nitrate nitrogen 

 for July, the month of greatest intake of nitrogen by the crop, was as follows: 



From Table 1 it may be seen that 1930 and 1931 were the years of the best 

 yield and quality of tobacco in this experiment. Thus, it appears necessary 

 to maintain through July a fairly high (65-75 p. p.m.) level of nitrate nitrogen 

 in order to insure optimum quality and high yield. The plants do not absorb 

 all this available nitrogen. Although tobacco has an extensive root system, 

 the roots do not occupy the soil sufficiently to withdraw all the available 

 nitrogen. In the north temperate zone, nitrates are almost invariably found 

 in soil growing intertilled crops. It is only in soil more completely occupied 

 by the roots of a crop such as grass that nitrates are not found in the growing 

 season. The soil on which the present experiment was run was underlaid by 

 gravel, and it is assumed, therefore, that a considerable proportion of soluble 

 nitrogen was lost in the drainage water. Some of it remained in the soil to 

 be absorbed by cover crops, weeds, and lower organisms of the soil. 



Burn tests made on "darks" and "seconds" of the crops of 1930 and 1931 

 showed no consistent differences in the burn of the darks, but the burn of the 

 seconds was slightly better from the plots which received 164.7 pounds of 

 nitrogen than from any other treatment. 



Form of Nitrogen Applied 



Long-established fertilizer practice in the Connecticut Valley has sanctioned 

 the use of a mixed fertilizer containing a high percentage of organic nitrogenous 

 material, particularly cottonseed meal. Inorganic sources of nitrogen have 

 generally been frowned upon by tobacco growers, and certain forms have been 

 studiously avoided. No doubt part of the aversion of the growers to inorganic 

 nitrogen is well founded in experience. 



This experiment was planned for the purpose of determining the effect of 

 two of the more common inorganic and two of the synthetic organic forms of 

 nitrogen on the yield and grade of tobacco when one half the total nitrogen 



