378 SOILS 



animal materials, as cottonseed meal, dried blood, 

 etc. Plants can feed on a nitrate but not on 

 organic nitrogen. It is necessary for the plant or 

 animal product to thoroughly decay, during which 

 process the organic nitrogen in it is changed into 

 a nitrate, before plants are able to use this kind of 

 food. This shows the value of knowing the source 

 of the different plant foods in a fertiliser. 



Nitrate of Soda (Chili Saltpetre), is the chief 

 commercial form of nitrogen as a nitrate. Large 

 deposits of this salt are found in the arid sections 

 of South America. It contains from 15.5 to 16 

 per cent, of nitrogen. Nitrate of soda is dissolved 

 in soil water almost immediately and becomes at 

 once available as plant food. For this reason it 

 should not be applied to land until the crop is 

 planted, or just before. It is especially valuable 

 for giving crops a quick start, and for promoting 

 a luxuriant leaf and stem growth. 



Dried Blood is collected from slaughter houses. 

 Red blood contains 12 to 14 per cent, of nitrogen, 

 and black blood 6 to 12 per cent. This material 

 decays very quickly in the soil, so that its plant 

 food is quickly available for crops. It is one of 

 the best sources of nitrogen. 



Cottonseed Meal usually contains 7 per cent, of 

 nitrogen, together with 1^ to 2 per cent, each of 

 potash and phosphoric acid. The nitrogen in it 

 is as quickly available to plants as that in dried 

 blood. This material can often be used to best 

 advantage, however, by feeding it to stock and 

 recovering most of the nitrogen in manure. 



Sulphate of Ammonia is a by-product in the 

 manufacture of boneblack, illuminating gas and 

 coke. It usually contains about 20 per cent, of 

 nitrogen, being the most concentrated source of 



