ENGLISH AGRICULTURE. 155 



manures. Farmyard manure is also a thoroughly genuine 

 substance. We know what it is ; and when it is made under 

 good conditions, it is difficult to imagine anything more fitted 

 for keeping up and adding to the fertility of the soil. 



Pass now to the consideration of some of these special 

 manures. There is a large number, but we can classify them 

 into two principal groups. One is the phosphatic group, and 

 the other the nitrogenous group. Plants require, and take 

 from the soil a considerable number of substances, but most 

 of these substances exist in the soil in inexhaustible quanti- 

 ties, and all efforts to persuade farmers to use gypsum, 

 magnesia, and potash salts have failed up to the present 

 time. 



It is in very few instances that the substances last named 

 are applied to the land with any marked effect whatever. 

 Phosphoric acid and nitrogen are two substances which are 

 not more important to the plant than any others, but as they 

 occur in the soil in too small quantities for the requirements 

 of the plant, they are always welcome. Phosphatic and 

 nitrogenous manures are the two principal restoratives which 

 commend themselves to the agriculturist, and phosphatic 

 manures appear to exert a most marked and positive effect 

 upon all the cruciferous crops. 



Cabbage, turnip, swedes, rape, mustard, kohl or kale, all 

 belong to one natural order, the Cruciferse, and are particu- 

 larly affected by the use of phosphates. On the other hand, 

 our graminaceous crops, such as wheat, barley, oats, rye, and 

 all the grasses, are at once affected in a marked manner by 

 the application of nitrogenous manures; so that as a general 

 principle we are led to prescribe phosphatic manures for root 

 and fodder crops, and nitrogenous manures for cereals and 

 grass crops. In this manner, during the rotation of crops, 

 the ground is enriched by both these important fertilizing 

 elements. 



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