Importance of Nitrogen to Growth of Plants. 231 



The total yield of field cured maize stover was almost identical upon 

 both the early and late plowed plats, being at the rate per acre of 4330 

 and 4313 pounds respectively, while the yield of grain was at the rate per 

 acre of 32.7 bushels on the early plowed and 26.0 bushels on the late 

 plowed plats or a difference of 25.8 per cent, in the yield of grain in 

 favor of early plowing. 



It thus appears that both plats started out in the early part of the 

 season to grow equal crops of maize, but in the latter part of the season 

 the late plowed plats fell behind. 



What caused this difference in yield ? Everyone must admit that the 

 percentages of moisture as found from week to week were not materially 

 different but that the proportion of available nitrogen was materially 

 different. It should be remembered that this being a season of drouth, 

 it would be expected that the per cent, of moisture would be the critical 

 factor, if it is ever modified by early and late plowing. Was, then, the 

 excess of available nitrogen the cause of the difference of yield, or did 

 the greater growth of maize on the early plowed plats, exhaust more 

 moisture? That is, did the maize plants on both plats take all the mois- 

 ture they could and finding more upon the early plowed plats, thus 

 produce more crops? If both the early and late plowed plats had been 

 kept entirely free from vegetation, would the early plowed plats have 

 shown a greater percentage of moisture than the late plowed? 



The average temperature throughout the four months was 68.8° F. 

 on the early and 70.4° F. on the late plowed plats. Quiroga says, " that 

 the amount of moisture in the soil seemed to be the controlling factor in 

 determining the temperature." However that may be, a prime difficulty 

 in assigning an influence to the temperature, is our lack of knowledge 

 as to whether the lower or higher temperature was the most desirable. 



Difference betzveen soil and subsoil. 



The relative amount of moisture and nitrogen in the first, second 

 and third foot of soil is not without some significance in this connection. 

 The new Athletic field has recently been stripped of its surface soil. 

 Why is this subsoil less productive than the soil? Is it on account of its 

 ability to hold water, or on account of the difference in available nitrogen, 

 or is it due to still other causes? 



The following table gives the relative quantities of moisture and 

 nitrogen at the three depths, including all determinations from April 6 

 to September 29: 



