20 MASS. EXPERIMENT STATION BULLETIN 333 



nitrogen than was produced by the legume subplots. 



Application of nitrogen to the legume crops appeared to be practically 

 needless. The nonlegume crops recovered only 43.3 percent of the nitrogen 

 supplied to them. 



Of the plots continuously without nitrogen, clover sod produced larger yields 

 of succeeding crops than did grass sod. Soybean stubble was less effective 

 than Japanese millet stubble. Hungarian millet was slightly better following 

 alfalfa plowed under than following barley plowed under. 



Analyses of the soils showed no evidence of accumulation of nitrogen by the 

 application of nitrogen fertilizers or by the growth of legume crops. Contin- 

 uous production of nonlegume crops did not measurably deplete the soil 

 nitrogen. Ratios of nitrogen to organic matter were slightly narrower when 

 legume crops occupied the plots without nitrogen fertilizers. From past rec- 

 ords of Field A and analytical data reported by the Experiment Station, it is 

 estimated that Plots 7 and 9 had produced from 1884 to 1889 six crops of 

 corn without nitrogen fertilizer which had contained a total of 20,520 pounds 

 per acre of dry matter and 241.4 pounds per acre of nitrogen. From the non- 

 legume subplots of these same plots, between 1925 and 1934 inclusive, six 

 crops of summer nonlegumes were produced, including two crops of sweet corn, 

 two crops of Japanese millet, and two crops of Hungarian millet. Weighed, 

 sampled, and analyzed, these crops contained 23,790 pounds per acre of dry 

 matter and 239.3 pounds of nitrogen. During the 40 intervening years the 

 plots had not received nitrogen fertilizers, and legumes had been eliminated 

 from the nonlegume subplots. The soil appeared capable of supplying to non- 

 legume crops growing during the summer months an average of 40 pounds per 

 acre of nitrogen, with no measurable depletion. 



Grasses and spring grains appeared to be unable to secure as large an amount 

 of nitrogen from the soil without nitrogen fertilizers. Microorganisms are less 

 active in the soil at springtime temperatures. 



Results obtained with the legume crops are in accord with the accepted facts 

 about the synthesis of nitrogen from the air by symbiotic bacteria in the soil. 

 Results with the nonlegume crops are strongly indicative of the presence in 

 the soil of nonsymbiotic microorganisms which are adding to the supply of 

 nitrogen that is available for such crops. 



Publication of this Document Approved by Commission on Administration and Finance 

 3m — 8-'36. No. 8410. 



