Manures and Fertilizers 121 



important sources of nitrogen. Cyanamid is diflBcult to 

 mix well in fertilizers and has other drawbacks. 



INIuch of the nitrogen of factory-mixed fertilizers comes 

 from organic sources. These are slower in their action, 

 as the organic forms of nitrogen must be changed first to 

 ammonia and then to nitrate before the plants can take 

 them up. Warm weather and warm soil are needed for this. 

 Dried blood is the best of the organic forms, with tankage, 

 fish scrap and cottonseed meal also used in different sec- 

 tions. Other more slowly available forms like leather, 

 animal bone and horn meal are nearly useless to the 

 potato crop unless treated with acid by the wet process to 

 make them more soluble. In comparing the prices of any 

 of these materials, the degree of availability must be 

 considered as well as the price a pound of the nitrogen. 

 It is unfortunate that state laws do not compel the state- 

 ment of the percentage of each of the principal forms in 

 which nitrogen is found in fertilizers as well as the total. 

 At present the nitrogen in as poor a material as dried peat, 

 often used as a drier in mixed fertilizers, counts as high in 

 the total percentage of nitrogen as from nitrate of soda 

 or dried blood. 



Nitrogen is so much more expensive than the other 

 elements of plant-food and so easily lost from the soil that 

 every effort should be made to conserve and increase the 

 soil supply by the use of rotations which provide plenty of 

 organic matter, including legumes, and by making soil 

 conditions as favorable as possible for the different soil 

 bacteria which take or change nitrogen. The other plant- 

 foods are in the soil in stable forms which are not easily 

 lost. Nitrogen exists largely in very unstable forms which 

 are easily lost in drainage water or by changing into the 

 gaseous form of nitrogen. 



