NITROGENOUS FERTILIZERS 157 



it furnished their chief supply of food. Opinion afterwards 

 swung to the opposite extreme, and it was generally held 

 that no organic matter is absorbed by agricultural plants. 

 Lately, however, it has been shown that many crops can use 

 nitrogenous organic matter, and an organic compound called 

 creatinin, that has been isolated from soil, was found to 

 produce a better growth of wheat seedlings than did sodium 

 nitrate. This may account in part for the high fertilizing 

 value of farm manure. Many crops, especially among 

 garden vegetables, are most successfully grown only when 

 supplied with organic nitrogenous materials. 



202. Forms of nitrogen in fertilizers. — There are many 

 different kinds of material used to provide nitrogen in com- 

 mercial fertilizers. Their value varies considerably, because 

 the nitrogen in some is not so readily available as it is in others. 

 In some the nitrogen is in the form of nitrate, in others am- 

 monia, but most of the mixed fertilizers contain some or all 

 of their nitrogen in the form of organic matter. 



203. Nitrate of soda. — This material is found in natural 

 deposits in northern Chili, where it is mined in enormous 

 quantities and shipped to most of the European countries 

 and to the United States. It is refined before shipment, 

 reaching this country nearly 96 percent pure. Between 15 

 and 16 percent of the total material is nitrogen. The im- 

 purities are not of a kind to be injurious to plants. 



This fertilizer is easily soluble in water and is readily ab- 

 sorbed by most farm crops. It is the most active form of 

 nitrogen. Because it does not need to be acted on by soil 

 organisms before being used by plants, it is of great value in 

 starting growjth-in the early spring, before the soil is warm 

 enough* to cause a conversion of the nitrogen of soil organic 

 matter, or of farm manure into nitrates. It will be remem- 

 bered that nitrates are largely washed out of the soil during 

 the fall and winter and that there is not usually enough 



