Relations of Higher Plants to the Formation of Nitrates 39 



The nitrates were uniformly higher in the soil planted to the mixture 

 than in the soil planted to a single crop, in spite of the fact that the draft 

 on the available nitrogen must have been nearly the same on both sections. 

 If it is true that the early stages of plant growth favor nitrification m 

 the soil, and that, as indicated by results already presented, maize is 

 much more effective in this respect than is millet, the higher nitrate 

 content under the mixture of maize and millet than under millet alone 

 is readily accounted for. 



This experiment, moreover, eliminates the factor of cultivation, to 

 which the higher nitrate content under maize has usually been ascribed. 

 With the maize plats receiving no more cultivation than the millet plats 

 and producing practically the same total quantity of dry matter, the higher 

 nitrate content of the maize soil must be due to some factor other than 

 cultivation. This again suggests the alternative of a beneficial influence 

 on nitrate production, or the utilization by the maize plant of nitrogen 

 in some other form than that of nitrates. 



The excessive supply of nitrates in soil planted to maize 

 Another significant fact brought out by a study of the nitrates 

 under maize is the great excess of nitrates over the apparent needs of 

 the plant during the first half of the growing season. Under oats and 

 millet there appears to be an increase of nitrates during the very early 

 stages of growth, but this quickly disappears as the growth of the plant 

 proceeds. Under grass there is little or no accumulation of nitrates at 

 any stage during the growth of the first crop of the year. Under maize, 

 however, the nitrates accumulate in apparently excessive quantity up to 

 the middle of the growing season, although during this time the crop is 

 growing actively and absorbing large quantities of nitrogen. 



In order to obtain some knowledge of the nitrogen absorption during 

 that period of the growth of the maize plant when nitrates were accu- 

 mulating in the soil, as compared with its later growth, the figures obtained 

 by Roberts and Wing (1888 and 1890) with the same variety of maize 

 (Pride of the North), and in the same field as that in which the experi- 

 ments with maize and millet were conducted in 1907, may be quoted. 

 In their experiment of 1888 the maize was planted on May 7 and was out 

 of danger of injury from frosts by September 10. Parts of the crop 

 were cut on different dates, weighed, and analyzed. From the weights 



