I3O SOILS AND FERTILIZERS 



Wheat, corn, and other crops grown on rich soils may 

 contain both nitrates and nitrites as normal constituents. 

 King reports nitrates in the growing crop in much larger 

 amounts than in the soil water. As the crop matures 

 the nitrate content of the plant declines. Calcium ni- 

 trate is the usual form, especially in soils which are 

 sufficiently supplied with calcium carbonate to allow 

 nitrification to progress rapidly. Nitrates and nitrites 

 are the most valuable forms of nitrogen for plant food. 

 Both are produced from the organic nitrogen of the soil. 

 A nitrate is a compound composed of a base element as 

 sodium, potassium, or calcium, combined with nitrogen 

 and oxygen. A nitrite contains less oxygen than a nitrate. 

 Potassium nitrate, KNO 3 , sodium nitrate, NaNO 3 , 

 and calcium nitrate, Ca(NO 3 ) 2 are the nitrates which 

 are of most importance in agriculture. The nitrites, as 

 potassium nitrite, KNO 2 , are present to a less extent 

 than the nitrates. Nitrates and nitrites are found in 

 surface well waters contaminated with animal and vege- 

 table matter. Many well waters possess some material 

 value as a fertilizer on account of the nitrates, nitrites, 

 and decaying animal and vegetable matters which they 

 contain. 



141. Ammonium Compounds of the Soil. - - The am- 

 monium compounds in a soil are usually less in amount 

 than the nitrates and nitrites. The sources are rain 

 water and the organic matter of the soil. The am- 

 monium compounds are all soluble and readily undergo 



