Relations of Higher Plants to the Formation of Nitrates 31 



In diagrams I (page 20), V (page 42), VI and VII (page 52), XVI 

 (page 64), XXVI (page 94), and XXVII (page 95) the moisture and 

 nitrate contents of the soils for the years 1908, 1910, 1911, and 1912 

 are shown graphically. In these diagrams both moisture and nitrates 

 in the planted and the unplanted sections of the plats are shown for one 

 to three crops each year. The diagrams serve to bring out plainly any 

 related changes that may occur in these two constituents of the soil. 



These diagrams sometimes show an increase of nitrates accompanying 

 or following a rise in moisture content, and sometimes a decrease, in 

 both the planted and the unplanted soil. A decrease in nitrates may be 

 due to leaching after a very heavy rainfall. This is strikingly shown 

 in the analyses following the heavy rain of September 1, 1912. In most 

 of the years included in these records there was a dry period during the 

 latter part of June or in July, and at this time the soil moisture usually 

 reached its minimum. As the soil moisture increased in August there was 

 generally an increase in nitrates in the unplanted soil; in the planted 

 soil, however, there was much less regularity in this relation and it varied 

 with the kind of plant grown on the soil. The nitrates in oat soil, for 

 instance, were usually not influenced by an increase in moisture content, 

 while under maize they sometimes responded to such an increase. 



Some relations between soil temperature and nitrate formation 



Records were kept of the soil temperatures taken daily at 4.30 p. m. 

 during the growing seasons of 1907 and 1908, at a depth of six inches on 

 certain unfertilized plats. In Table 8 are given the average temperatures 

 for the periods between the dates on which nitrates were determined, 

 also the nitrate content at the end of the period: 



TABLE 8. Averages of Daily Soil Temperatures at Depth of Six Inches for the 

 Periods Intervening between Nitrate Determinations on Cropped Soil 



Timothv, 1907 



June 7 to 13 



June 14 to 20 



June 21 to 

 July 24 



Plat 



Temperature (Fahrenheit) . 

 Nitrates (parts per million) 



711 



720 



711 



720 



711 



720 



60.0° 

 5 



60.5° 



65.3° 

 4 



66.5° 

 1 



.1° 



69.2° 

 3 



