84 T. Lyttleton Lyon and James A. Bizzell 



Considering first the nitrates formed by incubation of the natural, or 

 untreated, soil, it will be seen that on June 16 the maize-planted and the 

 bare soil showed approximately equal nitrate formation. At this time 

 the maize was about eight inches high. On the same date the soil from 

 the oats, which were about a foot high, gave less nitrate formation in the 

 planted than in the unplanted soil. On July 10 both the maize and the 

 oat soil produced more nitrates than did the bare soil. The maize soil 

 was particularly active in this respect. On October 9 nitrate formation 

 was less in the planted than in the unplanted soil. On July 10 the maize 

 had not yet started to tassel and the oats were in a late stage of bloom. 

 On October 9 growth had ceased. 



Incubation with dried blood on June 16 shows less nitrate formation in 

 the planted than in the unplanted soil of both crops. The mcubations 

 of July 10 show more nitrate formation in the planted soil, for both maize 

 and oats. With an abundant supply of organic nitrogen the nitrate- 

 forming bacteria were very active in the planted soil at this stage of growth, 

 which is an active stage for both these plants. These results are in line 

 with the results obtained by determmations of nitrates in the field; in 

 those tests it was sometimes found that during the active stages of growth 

 the nitrates in the maize soil were higher than those in the corresponding 

 unplanted soil. Nitrates under oats in the field were never so high as m 

 the bare soil. It v>^as concluded from analyses of the field samples that, 

 while the oat plant probablj^ stimulates the formation of nitrates during 

 some stages of its growth, the effect which it exerts in this way is not so 

 great as that produced by the maize plant. The results obtained by these 

 incubation tests show a greater nitrate production in the maize soil than 

 m the oat soil. 



There is one essential difference between nitrate formation in the field 

 soil and in the soil brought to the laboratory and placed in the mcubator: 

 the latter soil is thoroughly aerated, and some conditions favorable or 

 inimical to nitrate formation may be dispelled. 



On October 9 incubation tests were made only with the natural soil. 

 Nitrate production on that date was less in the planted soil. This is agam 

 in line with the results obtained from field samples, in which the nitrate 

 content was always very low under a crop during the later stages of growth 

 or after maturing. The incubation tests show a markedly depressing 

 influence for the oat crop and a slight depression for the maize crop. The 



