THE CHEMISTRY OF THE FARM. 419 



being far richer both in nitrogen and ash constituents than the mature 

 wood. 



THE ADAPTATION OF MANURES TO CROPS. The true economy of manure 

 can be understood only when we are acquainted with the special charac- 

 ters of the crops we cultivate. The composition of a crop is no sufficient 

 guide to the character of the manure appropriate to it, even when we possess 

 in addition the composition of the soil on which it is to be grown. It is not 

 only the materials required to form a crop, but the power of the crop to 



imilate these materials which must form the basis of our judgment. 

 This fact has been much overlooked by many scientific writers, who have 

 counselled farmers to manure their land in every case with all the consti- 

 tuents required by the crop, a proceeding both impracticable and unneces- 

 sary. 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 avail- 

 able 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. \Vc are thus able, by sup- 

 plying 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, 

 a large crop of mangels ; superphosphate alone, a large crop of 

 turnips ; while potassium salts alone may be strikingly effective with pas- 

 and clovers. 



This special manuring for each crop is no strain on the capabilities of 



if a rotation *>f crops be followed, I f superphosphate is applied 



for tin- turnips, potash for ( Eld a nitrogenous manure for the 



CCP ire important elements of pl.-u < >ntained in the 



soil will not lie diminished at the end of the rotation. At the same time 



t economic reeoll will have been obtained from the manures nn- 



6 will have hern supplied to that partieui 

 :i which it yields the most remunerative result. 



