CARBON AND NITROGEN CYCLES IN THE SOIL 83 



supplies of potassium salts and phosphates are present than on the 

 plots where these nutrients are less abundant and the crops smaller : 



Part of the absorbed nitrate remains in the root and stubble, and is 

 again added to the soil when the plant dies. Hence the percentage 

 of nitrogen in the soil is higher where the conditions are favourable for 

 the growth of plants than where, by the operating of some limiting 

 factor, plants cannot make full growth and therefore leave untouched 

 much of the nitrate to be washed away. 



Most of the data hitherto accumulated are incomplete, because they 

 refer only to crop results and take no account of nitrates washed out 

 in the drainage water : fuller data cannot be obtained without costly 

 and tedious lysimeter experiments. But in cases where the amount of 

 drainage is known to be small the incomplete data are still of value 

 for our purpose. 



4. There is no reason to suppose that the amount of nitrogen in a 

 prairie soil alters appreciably from year to year so long as the land is un- 

 touched. But directly ploughing and cultivation operations begin great 

 losses of nitrogen set in, as shown by Shutt's analyses of the Indian 

 Head soil, Saskatchewan (Table XXXV.). In this particular case 

 there is practically no drainage water, and therefore little or no washing 

 away of nitrates, yet only one-third of the lost nitrogen is recovered in 

 the crop. 



TABLE XXXV. LOSSES OF NITROGEN CONSEQUENT ON BREAKING UP OF PRAIRIE 

 LAND, TOP 8 INCHES. SHUTT (264). 



