102 



Physics of the Soil. 



Table , showing mean amounts of nitrates under different crops 

 between July 18 and Sept. ./, in Ibs. per acre of dry soil. 



When these amounts are expressed as parts per million 

 of the dry soil in the form of nitrogen, they stand 3.38, 

 1.61, 0.72 for corn; 3.87, 2.98, 1.00 for clover; 1.25 for 

 alfalfa and 6.99 for potatoes, and yet with these small 

 amounts of nitrogen in the soil during the time when the 

 chief growth was being made, large yields were produced. 



118. Limits of Nitric Nitrogen at Which Corn and Oats 

 Turn Yellow. Taking samples of soil from the surface 

 foot upon which oats were turning yellow and under adja- 

 "cent areas where the plants were normal green it was found 

 that two sets of duplicate determinations gave 



Oats yellow Oatj green. 

 (June 10 .025 .213 



Parts of nitric nitrogen per million of dry soil < 



(June 11 .027 .297 



These amounts, when expressed in pounds per acre and 

 as nitrates, are only .392 Ibs. and 3.843 Ibs., respoctively, 

 for the yellow and green oats. 



Table shoiving the amounts of nitric nitrogen under corn row* 

 where leaves are turning yellow and where. they are yet 

 normal green. 



