22 FERTILIZERS 



available. As nitrogen is the most expensive of all 

 fertilizing elements, the importance and economy of 

 a green cover crop ploughed under is considerable. 



NITROGEN FROM BLOOD AND TANKAGE, GUANO, ETC. 



31. The nitrogen from organic sources such as 

 blood, tankage, guano, is prompt and decided in its 

 action under ordinary growing conditions if the 

 materials are finely ground. If drilled or ploughed 

 under with the soil reasonably moist and warm, the 

 effect, of added growth or better color may be seen 

 in 30 days. The finer particles decay and become 

 available first, the coarser particles taking more 

 time. The plant thus has a steady, long feeding 

 period. Where fruit trees are grown during a long 

 growing period as in arid countries, the organic 

 forms of nitrogenous fertilizer are most satisfactory. 



NITROGEN FROM NITRATE OF SODA. 



32. This is an immediately available form of nit- 

 rogen. It dissolves easily in water and can thus be 

 carried down to the subsoil and leached away ac- 

 cording to the course the water takes. It is there- 

 fore, not so steady or long timed a feed for plants if 

 it is all applied at one time. It is better, therefore, 

 to make at least two applications during the grow- 

 ing period. One objection to its continued use, as 

 shown by Dr. King, is that in time the accumulation 

 of the soda will combine with the soil carbonates 

 and form carbonate of soda (black alklai) which in 

 certain quantities is deleterious to all forms of vege- 

 tation. Such a harmful accumulation may require 

 years but it will finally become positive. Neither 

 rains or irrigation will leach the soda away, if, as it 

 is claimed, all the rains of England have not leached 

 it away from the soils of Rothampstead Station. 



