Nitrate of Soda 



after a few years unless care is taken to use phos- 

 phates, and — nearly always — potash, in conjunction 

 with the nitrate. Contrary to what one often hears, 

 nitrate does not exhaust the soil, but in raising the 

 dose of nitrate to the level demanded by the Law 

 of the Minimum, the existing phosphoric acid and 

 potash are enabled to augment the yield to an 

 extent which they could not otherwise attain. 

 Nitrate, then, does not exhaust the soil, but 

 evidently requues to be used in conjunction with 

 other fertilising elements which, thanks to the 

 nitrate, the plants are able to absorb to the utmost, 

 and so give a more abundant crop. The farmer 

 should clearly understand the fact that manures 

 never exhaust the soil, and as nitrate of soda is a 

 manure therefore it is not exhaustive in its action. 

 As we saw in the chapter on the necessity of 

 manures, manure is all matter applied to the soil 

 for the purpose of augmenting the quantity of plant 

 food utilisable by the plants, and on the other hand 

 we learned from the Law of the Minimum that the 

 crops are proportionate — all conditions being equal 

 — to the amount of manure that the soil contains 

 in the least quantity ; referring further on to expor- 

 tation, restitution and importation. But in using 

 nitrate of soda, which constitutes a single manure 

 containing nitrogen only, it is necessary m order to 

 obtain any result that phosphoric acid and potash 

 should be present in the soil in proportion to the 

 quantity of nitrogen. This proves that the former 

 manuring was not right, that the soil was starved 

 for want of nitrogen, that it was nitrogen hungry 

 because the former manuring did not supply the 



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