22 EXPERIMENT STATION RECORD. [Vol.36 



There was a gradual decrease in the lime requirement of the soils from the 

 surface down to a depth of 30 in., except in the meadow soil. There was also 

 a more or less gradual decrease in the nitrogen and carbon content of the 

 different soils from the surface down to a depth of 30 in, . . , 



" Frozen soil, though showing a high bacterial content, did not give the 

 largest bacterial numbers through the year. . . . The time of maximum 

 bacterial numbers during the year varied with the different soils throughout 

 the year ; no two soils showed their maximum bacterial content at the time of 

 any one sampling." 



A list of 30 references to literature bearing on the subject is appended. 



Some factors that influence nitrate formation in acid soils, E. B. Peed and 

 E. J. Graui, (Soil Sci., 1 (1916), No. 4, pp. S17S38, pi. i ) .—Experiments con- 

 ducted at the Wisconsin Experiment Station with neutral gilt loam, acid sand, 

 acid silt loam, and acid peat soils are reported. " The following phases of 

 nitrification were investigated: (1) A study of the occurrence of nitrate- 

 forming bacteria in acid soils and their relation to the organisms commonly 

 found in neutral soils, (2) a comparison of nitrification of organic and inorganic 

 substances in acid and neutral soils, and (3) a comparison of the effect of 

 calcium carbonate on ammonification and nitrification of organic substances. . . . 



" It was found that the formation of ammonia from casein takes place so 

 rapidly in acid soils that for several weeks after the nitrogenous substance is 

 added the production of nitrates is not limited by lack of ammonia. The forma- 

 tion of nitrates in acid sand and acid peat takes place very slowly. In acid 

 silt loam or the neutral silt loam nitrification takes place much more rapidly. 

 The feeble nitrifying power of the sand and peat, as shown by inoculating 

 these soils with an active culture of the nitrifying bacteria, is largely due to 

 the condition of the soil. Apparently the nitrifying flora of silt loam when 

 transferred to a neutral soU is as active in the formation of nitrates as the 

 flora from silt loam. 



" In the case of the acid soils it seems that the nature of the compound to 

 be nitrified plays an important part. For example, in acid soils organic nitrogen 

 nitrifies much more rapidly than nitrogen from ammonium sulphate. In non- 

 acid soils the reverse is true — ammonium sulphate nitrifies more rapidly. This 

 is true regardless of the source of the nitrifying bacteria. 



" It seems that acid soils do not possess a strain of nitrifying bacteria espe- 

 cially resistant to soil acidity. In the presence of organic nitrogenous sub- 

 stances, as casein and gelatin, calcium carbonate did not permanently increase 

 the accumulation of nitrates. For a short interval, one or two weeks, calcium 

 carbonate stimulates nitrate formation ; later the reverse is true and there is a 

 decided decrease in the treated series. Apparently the reduction of nitrates is 

 largely due to bacteria. It has been found that in the treated soil there is an 

 enormous multiplication of the nitrate-assimilating bacteria. When stored 

 under conditions that prevent leaching, all of the soils showed a gain in nitrate 

 nitrogen. It seems that in silt loam nitrification increases soil acidity, and thus 

 it becomes necessary to add a basic substance in order to keep the process 

 going. . . . 



" Considering the data as a whole, it seems that under laboratory conditions 

 the beneficial effect of calcium carbonate on plant growth must be accounted 

 for by some processes other than the direct effect on nitrification." 



Studies in sulfofication, P. E. Brown and H. W. Johnson (Soil Set., 1 

 (1916), No. Jf, pp. S39S62). — Further experiments conducted at the Iowa Ex- 

 periment Station along the lines of those previously noted (E. S. R., 34, p. 19), 

 which were planned " to throw some light upon the problem of the relative 



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