82 THE CHEMISTRY OP THE FARM 



annual growth of beech wood contains on an average 

 about 10 lbs. per acre. The amount in the leaves and 

 seeds is much more considerable. Forest trees do not 

 produce seed till they are of mature age ; the seed is 

 formed at the expense of matter previously stored in 

 the tree. When the litter is not removed, the surface 

 soil will gain considerably in organic matter (contain- 

 ing both ash constituents and nitrogen) during the 

 earlier years of forest growth, and thus greatly improve 

 in value. 



Adaptation of Manures to Crops — Manures can be 

 used with true economy only when we are acquainted 

 •with the special characters 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 assimilate 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 constituents required by the crop, a pro- 

 ceeding 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 removed 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 grov/th may be obtained by supplement- 

 ing the stores of the soil with the few particular 



