Relations of Higher Plants to the Formation of Nitrates 73 



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DIAGRAM XXIV. 



Relative nitrate content of soil under oats followed by 

 maize, 1912 



The relation of the nitrate content of the soil to the quantities of nutrients 



removed by crops 



It has been suggested by a number of investigators that the bacterial 

 activity of the soil is dependent on the supply of readily soluble mineral 

 nutrients that it contains. Assuming this to be true, the question arises 

 whether a certain crop might influence the production of nitrates in the 

 soil by removing a greater or less quantity of the soluble mineral nutrients. 



As maize and oats have been grown in this experiment for a number of 

 years, it is possible to make some comparisons between these two plants in 

 regard to the quantities of nutrients removed and to the nitrate content of 

 the soil during the latter part of the season, when the removal of the 

 nutrient substances may be expected to affect the nitrate content. 



The crops removed from the plats used in these experiments were all 

 sampled and the total nitrogen was determined. Unfortunately, the ash 

 was not analyzed, therefore no exact figures are obtainable for the mineral 

 constituents; but, since the variation in yields between the two crops, 

 maize and oats, was very large, probalily the error introduced by employ- 



