REID AGRICULTURE ALLIED TO CHEMISTRY. 407 



may have abundance of what is wanted for another. The waste of 

 one crop that decays on the land or is returned as farm yard manure 

 furnishes food for the one that follows, and the tillage, by exposure 

 of the minerals of the soil to the air and sun and rain, promotes 

 their decomposition and consequent solubility, while facilitating its 

 power of absorbing ammonia from the atmosphere. In this way is 

 utilized a portion of the vast reserve of minerals or ash constituents 

 present in all soils, the soluble part of which had been more or less 

 removed by previous cropping. 



Regarding the influence of manure, it requires some variation 

 owing to the kind of crop, and different manures are suitable at 

 different stages of the growth of the same plant. Phosphoric acid, 

 potash and ammonia are largely demanded by all crops, and soils 

 are most rapidly exhausted of these constituents. 



Farmyard manure is the most universally applicable, but its 

 supply is very limited in proportion to its demand. It can be aided 

 or even supplemented by the judicious use of substances containing 

 nitrogen, such as guano, sulphate of ammonia, nitrate of soda, 

 rape cake, &c., and those containing phosphoric acid, such as 

 apatite, coprolites, bones or animal matter, superphosphate of lime, 

 mixed phosphates containing lime, magnesia, potash and ammonia, 

 as in " artificial" manures, guano, and those containing potash, as 

 the ashes of plants. 



Wheat and cereals demand a very large proportionate amount 

 of ammonia and next of phosphoric acid — silica, lime, etc., being 

 generally present in sufficient quantity* Potash is also largely 

 supplied by most soils. 



Turnips and root crops, though having as large a percentage of 

 nitrogen as cereals, and also the marked property of absorbing 

 ammonia from the atmosphere, and thus getting a quantum of 

 nitrogen, do not require it so much as manure. It is very service- 

 able after the plants have attained a vigorous growth, and should 

 be combined with carbonaceous manures and placed not too near 

 the seed, as their presence is prejudicial at an early stage, though 

 most necessary when approaching maturity for the development of 

 the weight of the bulb. The soluble phosphates are the most 

 demanded by turnips and root crops at an early stage of growth to 



