SUMMARY. 27 



lowing, aside from the one just mentioned, is the fact that favorable 

 conditions for chemical oxidation of the organic matter obtain because 

 of the more ready access of heat to the soil due to its exposed condi- 

 tion. So in an area such as is represented by this station where even 

 so far as moisture is concerned fallowing is questionable as a system, 

 the nitrifying flora would be served better by eliminating fallowing. 



SUMMARY. 



In the early part of spring the surface 6 inches of soil contained 

 more water-soluble nitrates than the lower 6-inch layers, and the 

 amount reached its maximum in the first layer in the first and second 

 weeks in May. 



From that time the amounts of water-soluble nitrates decreased in 

 the surface layer, and at4he same time the nitrates in the 12-inch 

 layer increased rapidly for one to two weeks, when a decrease was in 

 turn shown in that layer; similarly with the 18-inch and 24-inch 

 layers. 



Thus the successive 6-inch layers from the surface 6-inch layer 

 downward, at periods of about two weeks apart, each contained more 

 water-soluble nitrates than any other layer at the same date, and 

 each layer after accumulating a maximum amount showed a decided 

 decrease, which it never again made up. 



An exception was the 24-inch layer, which, while it showed the 

 same phenomenon as distinctly, did not at any time accumulate 

 more nitrates than any other layer, but underwent the same general 

 changes as the upper layers. 



The respective soil layers in the fallow plat reached their indi- 

 vidual maximum accumulation of nitrates about a week earlier than 

 the corresponding layers in the wheat plat. From June 12 to June 

 1 9 all soil layers in both plats suffered a general decrease in amounts 

 of water-soluble nitrates. This occurrence took place in the spring- 

 wheat plat in the same order and in about the same magnitude as in 

 the fallow plat. 



No evidence could be brought out that the wheat-plant roots 

 drew more heavily on the water-soluble nitrates in one 6-inch soil 

 layer than in any other at any time. The general decrease of nitrates 

 in all of the soil layers in the fallow plat masked any such reduction 

 by the wheat if any occurred. 



The corn plants at the end of their most active season of growth 

 had reduced the amounts of water-soluble nitrates in the soil to the 

 same degree of exhaustion as had the wheat plants in the correspond- 

 ing period of their development. The roots of the corn plants prob- 

 ably used the nitrates in the surface soil layer first, then drew most 

 heavily upon the 12-inch layer, and finally upon the 18 and 24 inch 

 layers. This progressive downward feeding of the corn roots occupied 



173 



