188 The Roots of Ulc lllieat Plant. 



that the chemical decomposition is more equable and certain than 

 in either separately ; and besides, the nitrate of soda has such a 

 great power of absorbing moisture, that in dry days and dewy 

 nights much good must result from it in this way : this effect is 

 pi'obably heightened by mixing salt with nitrate of soda. In land 

 tolerably well farmed, either after seeds or roots that have been 

 eaten off on the soil, or if removed a dunged winter fallow,* if on 

 light warm soils, nitrate of soda alone to the extent of 1 cwt. to 

 the ac:re mixed with an equal quantity of salt has been found 

 highly useful on the farm of the Royal Agricultural College : so 

 I am informed by the Professor of Agriculture. 



Soot, on stiff clay, usually called cold land, is the most con- 

 stant top-dressing for wheat ; this I have seen used for many 

 years past at from 20 to 40 bushels per acre, and consider it 

 useful not only from the ammonia and alkalis which it contains, 

 but also to some extent from its colour inducing a more de- 

 cided action of the sun's rays. It is upon this principle that the 

 upland farmer, on thin brushy land, objects to its use, as it burns 

 in dry weather. 



Other nitrogenous manures might be mentioned, especially 

 sulphate of ammonia and nitrate of potash, but in these their 

 great price is an objection to their extensive use. 



Salt, though not nitrogenous, is useful as a top-dressing on 

 other accounts. A friend of mine always tops from 1^ to 2 cwt. 

 per acre before ploughing the clover leys, in which case, besides 

 any chemical action, it may be of great use in killing the larvae 

 of insects and destroying slugs. He says : " I consider it useful 

 in checking an undue luxuriance of straw, and it decidedly re- 

 duces the amount of flag, and is, I think, of great use against 

 mildew. We always get brighter straw after salt." That salt 

 has a decided influence is now generally admitted. The chemist 

 accounts for it on the supposition that it renders the silicates more 

 soluble ; but whatever its cause of action it seems quite true that 

 though there is usually less straw when salt is employed, yet it 

 is generally of a finer texture and far better in colour. The pro- 

 fessor of agriculture at the Royal Agricultural College informs 

 me, in speaking of the mixture of salt with nitrate of soda, that 

 " though the salt is not without its beneficial effect, it is also 

 useful in facilitating the distribution of the nitrate." 



4. Lifting Action of Frost, cotmnonly called throiving out. — Soils 

 are very varied in their mechanical texture, according to which 

 they are liable to great changes under atmospheric influences, 

 amongst which the following are most common : — 



* In land which has been by some accident defrauded of the manure which 

 would ordinarily have fallen to its lot, the action of nitrate of soda is usually very 

 beneficial. 



