1921.] PUBLIC DOCUMENT — No. 31. 25 a 



together with peas and oats for two successive years. After 

 the peas and oats were cut and removed, these legumes have 

 come on well, and have produced a very satisfactory stand. 

 The rains during the past two years were frequent, which 

 favored their growth. If the season had been dry during the 

 development of the peas and oats, it is doubtful if the legumes 

 would have succeeded by this method of sowing. The clover 

 grew so fast as to enable us to make a cutting in early September. 



Respiration of Cranberries. — The study of cranberry respira- 

 tion was concluded in the early part of the year. The results 

 of the investigation and previous studies of chemical changes 

 during storage have been prepared for publication in a bulletin 

 which is now in press. 



Soil Studies. — A striking recurrence on the plots of Field A 

 in 1919, and again this spring, of the toxic effect on plant 

 growth of sulfate of ammonia led to a repetition of some of the 

 research work on the soils of plots 5 and 6, with reference to 

 the presence of soluble salts of manganese, iron and aluminum. 

 Large volumes of water extracts of the soils were prepared and 

 concentrated by evaporation. The residues were analyzed, and 

 amounts of manganese, iron and aluminum w^ere determined by 

 weight. There was found to be present at least 175 parts 

 sulfate of manganese in 1,000,000 parts of dry soil, equivalent 

 to 350 pounds in the upper 8 inches of an acre. This is suf- 

 ficient to be very poisonous to many kinds of plants. Aluminum 

 was present in much less quantity in the extract, and iron in 

 little more than traces. These results confirm the conclusions 

 of Ruprecht and Morse in previous bulletins of the Experiment 

 Station. A study of the history of the field for thirty-two 

 years has shown that injury on the plots receiving sulfate of 

 ammonia has been most marked in seasons when droughts have 

 occurred in the early summer. The addition of lime to the 

 soil prevents the injury by promoting the formation of sulfate 

 of lime instead of the other salts. Examination of limed soils 

 from these plots showed much smaller quantities of manganese 

 and aluminum in a soluble form, and larger quantities of lime. 



