8 MASS. EXPERIMENT STATION BULLETIN 346 



meal, preferably cottonseed meal. Animal sources, such as tankage, meat 

 meal, or fish meal, have not been considered satisfactory. The special virtue 

 of cottonseed meal lay in its ability to produce tobacco of good quality, but 

 the peculiar properties of this material which made it capable, of producing 

 tobacco of fine quality were not well understood. 



In the light of comparatively recent discoveries in plant nutrition, it now 

 appears that the virtue of cottonseed meal in producing tobacco of high quality 

 is due to two qualities. First, being a difficultly soluble organic material, it 

 must undergo decomposition in the soil before its nitrogen becomes available 

 for plant growth. This process continues through all or most of the growing 

 season, and insures abundant nitrates in the soil at critical growth periods. 

 Researches at this station (5) have proved that cottonseed meal is not utilized 

 by the tobacco plant until it is decomposed. Nitrates, the final end product 

 of protein decomposition, were found to be the form of nitrogen most readily 

 assimilated by tobacco. Second, in recent years it has been discovered (6) 

 that Connecticut Valley tobacco soils are frequently deficient in available 

 magnesium unless it has been supplied artificially, and that tobacco is one of 

 the plants most sensitive to magnesium deficiency. Cottonseed meal, in 

 quantities in which it has been used for growing tobacco in the Valley, carries 

 sufficient magnesium to make up for the natural deficiency of the soil, and 

 that, no doubt, is one reason why it has produced good tobacco. But now 

 that the need of magnesium in the Valley soils has been demonstrated, cheaper 

 and satisfactory inorganic sources have been developed. Possibly there are 

 other properties of cottonseed meal besides those mentioned which contribute 

 to its value as a tobacco fertilizer. 



The present experiment was undertaken for the purpose of seeing to what 

 extent, if any, the proportion of organic nitrogen in the tobacco fertilizer 

 could be reduced below that in the standard formula without reducing yield 

 or impairing quality materially. The phosphoric acid and potash of the 

 fertilizer were the same as in that used in the previously mentioned experi- 

 ments. Plots were also of the same size and in quadruplicate. The organic 

 source of nitrogen was cottonseed meal, and the inorganic sources were mix- 

 tures of nitrate of soda and sulfate of ammonia in such proportions as to 

 furnish equal quantities of nitrogen. It is not claimed that this is the best 

 combination of nitrogenous fertilizers, but from the previous experiment it was 

 considered safe. It is quite possible that more nitrate and less sulfate, or the 

 addition or substitution of urea or calcium cyanamid would have produced a 

 better mixture. The results of this experiment are summarized in Tables 5 

 and 6. 



Table 5. — Mean yield and grade of tobacco grown with fertilizer 

 IN which the ratio of organic to inorganic nitrogen varied, 1932-1935 



