Il8 SOILS AND FERTILIZERS 



in meadow land there is a tendency for the nitrogen 

 to increase. These facts are well illustrated in the 

 investigations of Lavves and Gilbert, at Rothamsted. 43 



Age of pasture. Nitrogen. 



Years. Per cent. 



Arable land o. 14 



Barn- field pasture 8 o. 151 



Apple-tree pasture 18 o. 174 



Meadow 21 0.204 



Meadow 30 0.241 



After deducting' the amount of nitrogen in the manure 

 added to the meadow land, the annual gain of nitrogen 

 was more than 44 pounds per acre. 



Another source of gain of nitrogen is the fixation of 

 the free nitrogen of the air by the growth of clover 

 and other leguminous crops.  If a soil is properly 

 manured and cropped the amount of nitrogen may be 

 increased. A rotation of wheat, clover, wheat, oats, and 

 corn with manure will leave the soil at the end of the 

 period of rotation in better condition as regards nitro- 

 gen than at the beginning. These facts are illustrated 

 iii the following table: 17 



Continuous wheat culture — 



Nitrogen in soil at beginning of experiment 0.221 per cent. 



Nitrogen at end of 5 years continuous wheat cultiva- 

 tion °- 1 93 " 



Loss per annum per acre (in crop 24.5, soil 146.5) . . 171 pounds. 



Rotation of crops — 



Nitrogen in soil at beginning of rotation 0.221 per cent. 



Nitrogen at close of rotation 0.231 " " 



Gain to soil per annum per acre 61 pounds. 



Nitrogen removed in crops per annum 44 



