NITROGENOUS MANURES 121 



gen has been plowed under, and is beyond the reach 

 of the young plants when they require the most help 

 in obtaining food. The various methods of cultiva- 

 tion as deep and shallow plowing, spring and fall 

 plowing, and surface cultivation have as much influ- 

 ence upon the available nitrogen supply of crops as 

 upon the water supply. The saying that cultivation 

 makes plant food available is particularly true of the 

 element nitrogen, the supply of which is capable of 

 being increased or decreased to a greater extent than 

 that of any other element. 



NITROGENOUS MANURES 



152. Sources of Nitrogenous Manures. The mate- 

 rials used for enriching soils with nitrogen, to promote 

 crop growth, may be divided into two classes : (i) 

 organic nitrogenous manures, (2) mineral nitrogenous 

 manures. Each of these classes has a different value 

 as plant food, and in fact there are marked differences 

 in fertilizer value between materials belonging to the 

 same class. The nitrogenous organic materials used 

 for fertilizing purposes are ; dried blood, tankage, 

 meat scraps and flesh meal, fish offal, cottonseed meal, 

 and leguminous crops as clover and peas. The nitro- 

 gen in these substances is principally in the form of 

 protein. When peat and muck are properly used 

 they also may be classed among the nitrogenous 

 manures. The mineral nitrogenous manures are 

 nitrates, as sodium nitrate, and ammonium salts, as 

 ammonium sulphate. 



123. Dried Blood. This is obtained by drying 



