DISCUSSION OF RESULTS OF DETERMINATIONS. 15 



accumulation of water-soluble nitrates just one week later in the 

 wheat plat than in the fallow plat. It will be remembered that it 

 was stated that the fallow plat was plowed to a depth of about 8 inches 

 in the spring of 1908 and that the wheat plat had not been plowed 

 since being backset in the previous fall to about 5 inches deep. There 

 was thus a difference in the mechanical condition of the two plats ; the 

 summer-fallow plat being more open and stirred to a greater depth, 

 there was presumably a more rapid access of air, and in consequence 

 a more rapid rise in temperature. Hunt a also found that early plow- 

 ing promoted nitrification more rapidly than late plowing, and pre- 

 sumably early plowing would promote nitrification more rapidly than 

 no plowing at all. 



It was expected that some information would be obtained in regard 

 to the rate at which the growing wheat plants removed the nitrates 

 from the different soil layers, that being one of the main points 

 sought for in the work. As a matter of fact, it will be noticed that 

 the curves of the two figures are so much alike in the general trend 

 that were they not scaled or labeled in any way it would be difficult 

 to say which figure represented the fallow plat and which the wheat 

 plat. The shifting of the dates of the maximum accumulation of 

 nitrates in the individual soil layers one week back in the case of the 

 fallow plat might be explained by the difference in the tillage. By 

 using the fallow plat as a check on the wheat plat, which is really 

 what it is, it will be noticed that aside from this shifting already 

 mentioned the only general differences are the smaller amounts of 

 nitrates found in the wheat plat and that after June 19, when the 

 general decrease in nitrates took place — as in the fallow plat- — the 

 nitrates in each soil layer in the wheat plat were more constant in 

 both total amounts and amplitude of variation. Had the results 

 on the fallow plat not been obtained as a check on the results ob- 

 tained on the wheat plat, it might have been supposed that during 

 the time immediately following June 12, when the wheat plants 

 were making rapid increase in growth, the crop was removing nitrates 

 much more rapidly than they were being formed. Even thus one 

 would hardly expect the nitrates to be removed so spontaneously and 

 almost completely from each 6-inch soil layer. One can not, then, 

 from the amounts of water-soluble nitrates found, determine the soil 

 layers in which the wheat roots were feeding most rapidly or demon- 

 strate any progressive downward ranging of the roots as the season 

 advanced. The apparent "removal" of the nitrates from the soil 

 is due, then, to some other factor than the presence of the crop. 



Even after June 19, when the marked decrease in the amounts of 

 water-soluble nitrates occurred, there is no consistent correlation 



a Hunt, T. F., loc. cit. 

 173 



