46 THE CHEMISTRY OF THE FARM. 



writers, who have counselled farmers to manure their land 

 in every case with all the constituents required by the 

 crop, a proceeding both impracticable and unnecessary. 

 In the case of a barren sand it may indeed be requisite to 

 supply all the constituents of plant food before a crop can 

 be grown, but such a case is far from the circumstances of 

 ordinary agriculture. 



When land is in a fertile condition the total amount of 

 plant food available for crops is very considerable, and 

 luxuriant growth may be obtained by supplementing the 

 stores of the soil with the few particular elements of food 

 which the crop it is wished to grow has most difficulty in 

 obtaining. Thus, in a large majority of cases, a dressing 

 of nitrate of sodium and superphosphate will ensure a full 

 crop of wheat, barley, or oats, and in many cases nitrate 

 of sodium alone will prove very effective. These cereal 

 crops generally find the supply of nitrates in the soil 

 insufficient for their full growth, and the supply of 

 phosphates more or less inadequate ; but in a majority of 

 cases they are well able to obtain a sufficient supply of 

 potash, and other essential elements of food. We are 

 thus able, by supplying one or two constituents of the 

 crop, to obtain a luxuriant harvest. In the same way 

 nitrate of sodium employed alone will, in most cases, 

 produce a large crop of mangels ; superphosphate alone, a 

 large crop of turnips ; while potassium salts alone may be 

 strikingly effective with pasture and clovers. 



This special manuring for each crop is no strain on the 

 capabilities of the soil if a rotation of crops be followed. 

 If superphosphate is applied for the turnips, potash for 

 the seeds, and a nitrogenous manure for the cereal crops, 

 the more important elements of plant food contained in 



