452 SOILS: PROPERTIES AND MANAGEMENT 



370. Effect of soil aeration on nitrification. — Probably 

 the most potent factor governing nitrification in the soil 

 is the supply of air. In clay, and even in loam soils, the 

 tendency to compactness is such as to prevent the pres- 

 ence of sufficient air to enable nitrification to proceed 

 as rapidly as desirable unless the soil is well tilled. Col- 

 umns of soil eight inches in diameter and eight inches in 

 depth were removed from a field of clay loam on the Cor- 

 nell University farm, and carried to the greenhouse with- 

 out disturbing the structure of the soil as it existed in 

 the field. At the same time, vessels of similar size were 

 filled with soil dug from a spot near by. These may be 

 termed unaerated and aerated soils. Both were kept 

 at the same temperature and moisture content in the 

 greenhouse, but no plants were grown on them. The 

 production of nitrates was as follows : — 



371. Effect of sod on nitrification. — Nitrification 

 proceeds slowly on sod land, especially if the soil is heavy. 

 On the same type of soil as that used in the experiment 

 last described, the average quantities of nitrates for each 

 month of the growing season in the surface eight inches 

 of sod land, as compared with maize land under the same 

 manuring, were as follows : — 



