Relations of Higher Plants to the Formation of Nitrates 25 



Relation of nitrates to soil moisture on the plats 



Moisture determinations were made in all soil samples in which nitrates 

 were determined; in addition, daily determinations of moisture were made 

 in certain of the unfertilized plats during the summers of 1907 and 1908. 

 It was thought that a record of the moisture content for a period preceding 

 the nitrate determinations would show the relation between soil moisture 

 and nitrate formation better than would a statement of the moisture con- 

 tent on the day on which nitrates were determined. The nitrate content 

 and the average moisture content of the soil for the time intervening 

 between the dates on which nitrates were determined are given in Table 4 : 



TABLE 4. Averages of Daily Determinations of Soil Moisture for the Periods 

 Intervening between Nitrate Determinations on Cropped Soil 



Timothy, 1907 





June 4 to 6 



June 7 to 13 



June 14 to 20 



June 21 to 

 July 24 



July 25 to 

 August 14 



Plat 



711 



720 



711 



720 



711 



720 



711 



720 



711 



720 



Moisture (percentage) 



Nitrates (parts per million) . 



22.8 

 3 



26.3 

 2 



23.4 

 5 



26.3 

 2 



23.8 

 4 



27.0 



1 



21.7 

 5 



25.1 

 3 



17.9 



7 



21.2 

 6 



Maize, 1908 





June 2 to 22 



June 23 to 

 July 6 



July 7 to 27 



July 28 to 

 August 10 



Plat 



711 



720 



711 



720 



711 



720 



711 



720 



Moisture (percentage) 



Nitrates (parts per million) 



22.7 

 40 



22.6 

 31 



21.1 

 62 



21.5 

 102 



24.0 



182 



25.3 

 211 



22.1 

 162 



22.8 

 136 



In 1907 the moisture content was perceptibly lower and the nitrates 

 were higher in plat 711 than in plat 720. In 1908 there was little dif- 

 ference in moisture in the two plats and no consistent difference in 

 nitrates. In the latter part of July and the first part of August there 

 was a decrease in moisture content in both plats each year; in 1907 this 

 was accompanied by an increase in nitrates, while in 1908 a decrease in 

 nitrates occurred. The drying out of the soil and consequent aeration 

 does not appear to produce the same result in both cases, from which 



