128 PLANT DISEASE 



OXIDE OF IRON AND AMMONIA 



In Elements of Agriculture, already referred 

 to, page 19 



" Oxygen combines with iron in several 

 different proportions, and the change in the 

 colour of a subsoil from a bright yellow to a 

 rusty brown may be due to the bright yellow 

 oxide of iron becoming more thoroughly oxid- 

 ised when the subsoil is exposed to the air at 

 the surface." 

 On page 20. 



In the analysis of four different soils 

 the oxide of iron is . -92, 577, 3*63, 1*52 

 and the ammonia in the 



same analyses . '15, '19, '23, *2i 



so proving that the percentage of iron in the 

 soil has not in itself the means of fixing the 

 percentage of ammonia. 



Since a perfect oxidation of the iron in the 

 soil can only go on through a thorough contact 

 with the air, it follows that a thoroughly 

 aerated soil will have its iron better oxidised 

 and consequently better able to take up 

 ammonia from the air. 



Hence a better nitrification will go on in an 



