QUANTITY OF NITRATES FORMED 235 



soil. These findings, however, are contrary to those of Wojtkie- 

 wicz, who found the maximum number of organisms to occur in 

 soil during the spring and the minimum in the winter. He also 

 notes a correlation between bacteria present and the amount of 

 nitrates in the soil. 



Climate influenced the nitrifying powers of the soil, and Hilgard 

 taught that the nitrifying powers of the arid soils are -superior to 

 those of the humid soils, but the extensive work by C. B. Lipman, 

 both by laboratory and field experiments, in which soils have been 

 transported from humid to arid districts, and vice versa, has shown 

 just the opposite to be true namely, that the biological activities 

 of a soil are more pronounced under humid than under arid 

 conditions. 



Quantity of Nitrates Formed. The quantity of nitrates produced 

 in a given soil varies with all of the factors which have been con- 

 sidered; hence, any results obtained must be interpreted with 

 this in mind. The greatest rate of nitrification noted by Warington, 

 when working with an ordinary arable soil from the Rothamsted 

 farm, yielded 0.588 parts of nitrogen per million of air-dried soil 

 a day. Similar soil supplied with ammonium chlorid nitrified 

 about 0.924 parts per million in the same time. 



Lawes and Gilbert, working with the far richer Manitoba soils 

 and with a higher temperature, obtained in two cases (soils from 

 Selkirk and Winnipeg) average daily rates of nitrification of 0.7 

 parts of nitrogen per million during three hundred and thirty-five 

 days, the rates during the early portion of this period being as high 

 as 1.03, 1.24, 1.36 and 1.72 per million. 



Deherain, working with a soil containing 0.16 per cent, of nitro- 

 gen, obtained daily rates of nitrification varying from 0.71 to 1.09 

 per million in ninety days. Working with a richly manured soil 

 containing 0.261 per cent, of nitrogen, he obtained a maximum 

 daily rate of nitrification during forty days of 1.48 of nitrogen 

 per million of soil. 



At times the difference in nitrification noted in different soils 

 may be due to a difference in physiological efficiency of the nitrify- 

 ing ferment, as Marcille compared the nitrifying powers of three 

 different soils and found that the poorest yielded an organism 

 nitrifying less rapidly than the others. Some soils nitrify ammonia 

 more readily, while others nitrify cotton-seed meal more rapidly. 

 This must be due to differences in the metabolism of the organism 

 found in the various soils. 



Hutchinson considers this variation at times due to toxins which 

 develop under anaerobic conditions produced by water saturation. 

 Subsequent aeration removes the toxic condition and the formation 

 of nitrates takes place. He also found copper had a decided 



