86 



T. Lyttleton Lyon and James A. Bizzell 



two jfirst-mentioned pots contained Volusia silt loam and the other two 

 contained Dunkirk clay loam. 



On December 28, 1911, pots 127 and 343 were placed in a building in 

 which the temperature corresponded closely with that of the outside 

 air but the moisture content of the soil could be controlled. Pots 128 and 

 344 remained in the greenhouse. All the pots were kept bare of vegeta- 

 tion and were maintained at a moisture content of about 25 per cent of the 

 dry weight of the soil. On February 28, 1912, pots 127 and 343 were 

 returned to the greenhouse. During most of the time that they were in 

 the outside building they were frozen, and two or three times they thawed. 

 They stood in the greenhouse with pots 128 and 344 until March 4, when 

 all were brought to the laboratory and nitrates were determined. The 

 results are shown in Table 33: 



TABLE 33. 



Nitrates in Soils Subjected to Freezing and in Similar Soils 

 Remaining Unfrozen 



Pot 



Kind of soil 



Treatment 



Nitrates 



(parts per 



million) 



127 



Volusia silt loam 



Volusia silt loam 



Dunkirk clay loam .... 

 Dunkirk clay loam .... 



Frozen 



155 



128 



Unfrozen 



Frozen 



Unfrozen 



112 



343 



92 



344 



70 







It would appear from this table that freezing produces a condition of 

 soil favorable for nitrate formation. The well-known action of frost in 

 producing a granular condition of a clay soil may have operated to some 

 extent to bring about this condition. To what extent the more active 

 production of nitrates is due to aeration and to what extent it is due to cold, 

 it is impossible to say; but the obvious effect is to overcome the depressing 

 influence of the crop previously grown and to permit the resumption of 

 nitrate formation required for the growth of the crop that follows. 



The depressing influence of grass on nitrate formation a possible factor in 



orchard management 

 The experiments by Deherain and by Leather, already cited, indicate 

 that all the plants tested except maize depressed the formation of nitrates 



