SOIL AND SUBSOIL. I 4 ! 



Correspondingly, Ladd 1 has shown that with the increase of 

 humus in the soil, there is also a corresponding increase in the 

 amounts of mineral plant-food extracted from the soil by a 

 four per cent solution of ammonia, such as is employed in the 

 Grandeau method of humus-determination. 



1 Bull., S. Dakota Station, Nos. 24-32, 35, 47. 



