A STUDY IN SOIL NITROGEN 



By F. W. Morse, Research Professor of Chemistry 1 



INTRODUCTION 



The history of "Field A" of the Massachusetts Agricultural Experiment 

 Station has been recorded continuously since 1882, when the field was regarded 

 as "run-out grassland." A review of its history up to 1921 has been published 

 in Bulletin 290 (1932). The construction of the Goessmann Chemistry Lab- 

 oratory in 1922 necessitated abandoning Plots 0, 1, 2, 3, and 4. The numbers 

 of the remaining plots — 5, 6, 7, 8, 9, and 10 — were retained in order to 

 avoid confusion. 



Longfellow yellow flint corn was grown in 1922 and 1923 with the fertilizer 

 plan described in Bulletin 290. The data of 1922 were the basis for retaining 

 the plots mentioned. The crop of 1923 was in preparation for the new exper- 

 iment, which was to begin with clovers and grasses seeded in the corn. 



Plots 7 and 9 were the key plots in the new study, because they had not 

 received any nitrogen in fertilizers since sometime before 1882. Few analyses 

 had been made of crops actually grown on these plots, but many analyses of 

 the same kinds of crops were at hand. From these data it was calculated that 

 the crops taken from these plots in forty-one harvests, 1883 to 1923 inclusive, 

 had contained nitrogen equivalent to an average of 2,700 pounds per acre. 

 The leguminous crops taken from the plots during this period possibly con- 

 tained 1,270 pounds, leaving 1,430 pounds in the nonleguminous series. 



The object of the new experiment was to measure the nitrogen recovered in 

 the continuous production of nonleguminous crops and in rotations in which 

 leguminous crops alternated with nonleguminous crops. 



PLAN OF EXPERIMENT 



Each plot in the original "Field A" was 8 rods long by 2 rods wide and 

 contained Ho acre. For this experiment every plot was divided into four sub- 

 plots, 2 rods square and containing y 40 acre each. This permitted duplicate 

 area? of legumes and of nonlegumes on each numbered plot. 



The fertilizers differed but little from those formerly used. All plots received 

 superphosphate and sulfate of potash equivalent to 80 pounds phosphoric acid 

 and 125 pounds actual potash per acre. Plot 5 received nitrate of soda; Plot 

 8, sulfate of ammonia; and Plot 10, dry ground fish — in each case an amount 

 furnishing 45 pounds nitrogen per acre. Nitrogen was withheld every other 

 year in order to measure any residual nitrogen from the fertilizers. Plots 6, 

 7, and 9 did not have nitrogen fertilizers. 



Changes from the previous fertilizer plan were the substitution of sulfate of 

 potash for muriate on all plots, and of nitrate of soda for sulfate of ammonia 

 on Plot 5, and the withholding of nitrogen from Plot 6 which heretofore had 

 received sulfate of ammonia like Plot 8. 



Table 1 shows the arrangement of the plots and subplots. 



1 This publication was prepared after the author's retirement from active service in December 

 1935. 



