2IO SOILS AND FERTILIZERS 



tilizer, as a rule, the better it is for promoting crop 

 growth. Some combinations of plant food produce 

 fertilizers which become so hard and lumpy that it is 

 difficult to crush the lumps before spreading. The 

 mass must be pulverized so as to be evenly distributed, 

 otherwise the plant food will not be economically 

 used. A fertilizer that passes through a sieve with 

 holes 0.25 mm. in diameter is more valuable and can 

 be used to better advantage than one of the same com- 

 position that requires a 0.5 mm. sieve. 



269. Forms of Nitrogen in Commercial Fertilizers. 



— Nitrogen is present in commercial fertilizers in three 

 forms : (1) Ammonium salts,(2) nitrates, and (3) organic 

 nitrogen. The organic nitrogen is divided into two 

 classes : (a) soluble in pepsin solution, and (b) insolu- 

 ble in pepsin solution. The relative values of these 

 different forms of nitrogen are discussed in Chapter 

 IV. Three fertilizers may have the same amount of 

 total nitrogen and still have entirely different crop- 

 producing powers. 



No. 1. No. 2. No. v 

 Nitrogen as : Per cent. Per cent. Per cent. 



Ammonium compounds ... 1.75 0.25 o. 10 



Nitrates 0.15 0.15 o. 10 



Organic nitrogen : 



Soluble in pepsin o. 10 1.25 0.55 



Insoluble in pepsin 0.35 1.25 



Total 2.00 2.00 2.00 



In purchasing fertilizers it is important to know not 

 only the amount of nitrogen, but also the form in 



