Relations of Higher Plants to the Formation of Nitrates 81 



alfalfa, and then the nitrates under timothy are compared with those in the 

 bare soil previously planted to timothy, it is evident that the nitrates are 

 relatively much lower under alfalfa. As the nitrates in the unplanted 

 soil represent the available nitrates for each crop, it is apparent that 

 alfalfa either has a much greater effect than has timothy in inhibiting 

 nitrate formation or is using more nitrates than is timothy. But it has 

 been shown previouslj^ that alfalfa has a stimulating effect on nitrate for- 

 mation as compared with timothy. It must be concluded, therefore, that, 

 under similar conditions, alfalfa on this soil is absorbing more nitrates than 

 is timothy. 



Since there was some doubt in regard to the relation that these two 

 crops may have to the nitrate content of the soil below the surface foot — 

 especially as alfalfa is a much deeper-rooting plant than timothy — the 

 soil was sampled on July 6, 1910, to a depth of four feet and the samples 

 from each foot were analyzed separately. The same number of borings 

 were taken for these analyses as for the others. Both the planted and 

 the unplanted sections of the plats were sampled. The results of the 

 analyses are given in Table 31. 



It is seen from this table that the depths below the surface foot contain 

 very small quantities of nitrates under both crops, and even in the 

 unplanted soil the nitrates belov/ the first foot do not change the relations 

 that exist in the surface soil. The samples were taken in midsummer, 

 when the nitrates would have had ample opportunity to leach into the 

 lower soil; they were obtained five years after the crops were planted, 

 during which time the alfalfa roots had penetrated much beyond the upper 

 four feet of soil. It may safely be assumed that the nitrates in the first 

 foot of soil under these crops give an adequate conception of the relative 

 nitrate content of both crops. 



Nitrifying activity of soil under crops as shown by inoculation tests 

 Further experiments were conducted with maize, oats, and bare soil, in 

 which the nitrifying activity of the soil from a number of the plats was 

 maintained at a temperature favorable for nitrification and at an optimum 

 moisture content for a number of days, both when dried blood was added 

 to the soil and when the soil was untreated. The object in adding dried 

 blood was to have in the soil an abundance of easily ammonifiable and 

 nitrifiable organic matter and thus eliminate the errors that might arise 



