338 MASS. EXPERIMENT STATION BULLETIN 260 



In the experiments with quantity of phosphorus, attempt has been made 

 tc measure the stimulative eflfect on the growth of tobacco of large ap- 

 plications of superphosphate, rather than to determine the optimum nu- 

 trient requirement of tobacco for phosphorus. During the first season, 

 1928, when one-half, one, two, and four tons of superphosphate per acre 

 were applied in addition to that in the regular tobacco fertilizer, notable 

 increases in yield were obtained, the maximum being from the two-ton 

 treatment. In 1929 much larger yields were obtained, but there was no 

 response to the excessive applications of superphosphate. In another 

 experiment, however, the yields were markedly stimulated by four tons 

 of superphosphate. A very interesting feature of these experiments has 

 been the observation on maturity. Contrary to what is generally ex- 

 pected from excessive applications of phosphorus, there has been no 

 evidence that the tobacco has matured unusually early or any differently 

 from that not receiving the extra phosphorus. 



The Magnesium Requirement of Certain Common Crop Plants. (J. P. 



Jones and M. E. Snell). This experiment was started in the season of 

 1929 and is a redirection of previous work which had shown a magne- 

 sium deficiency in the soil of one of the old experimental fields at the 

 Station, illustrated by certain symptoms on both corn and tobacco. The 

 work as now outlined consists of an attemj^t to observe the symptoms of 

 a lack of magnesium on several of the commonly grown crops, such as 

 onions, clover, timothy, alfalfa, and potatoes. The season was too dry 

 in 1929 to permit a satisfactory growth of these crops; hence the observa- 

 tions made are not considered sufficiently satisfactory to draw conclusions 

 at this time. It has also been proposed in connection with this work to 

 make some chemical studies of this and other soils, hoping to account 

 more definitely for the lack of magnesium. Progress is being made on 

 this phase of the work, but no results can be included in this report. 



DEPARTMENT OF BACTERIOLOGY AND PHYSIOLOGY 

 G. E. Gage iii Charge 



Nitrogen-Fixation in Relation to Legumes and Non-Legumes under De- 

 fined Agronomic Conditions. (James E. Fuller). This project has been 

 followed out as outlined for the last year: namely, to study soils of differ- 

 ent units to determine the ability of these units to fix atmospheric nitrogen; 

 to isolate organisms from the units and study the distribution of nitrogen- 

 fixation organisms as compared with the nitrogen-fixation power of the 

 soil units; and lastly, to study factors which may influence the presence and 

 activity of nitrogen-fixing organisms isolated in the studies. The pre- 

 liminary phase of this project has been completed and has been written 

 up and accepted for publication by Soil Science. It wiU appear in the 

 next May or June issue of that journal. The first part of this study was 

 carried on by Dr. Leon A. Bradley and was taken over in 1928 by Dr. 

 James E. Fuller. A summary of this preliminary investigation as carried 

 out on an experimental field (Field A) divided into twenty-four plots, 

 Has furnished the following information. 



