56 THE CHEMISTRY OF THE FARM. 



given in the table, excepting mangels. This large pro- 

 duce is obtained by a very small consumption of soil food ; 

 the amounts of potash and phosphoric acid required are 

 especially far less than in the case of any farm crop. 

 The greater part both of the ash constituents and nitrogen 

 is found in the fallen leaves; if these are left undis- 

 turbed, and allowed to manure the ground, the require- 

 ments of the forest become extremely small, far smaller 

 than in ordinary farm culture. It appears that about 

 3000 Ibs. of perfectly dry pine timber are produced with 

 a consumption of only 2J Ibs. of potash, and 1 Ib. of 

 phosphoric acid per acre per annum : with beech timber 

 the quantities required are rather larger. The amount of 

 nitrogen in timber is very small ; the annual growth of 

 beech wood contains on an average about 10 Ibs. per acre. 

 The amount in the leaves and seeds is much more con- 

 siderable. 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 (containing both ash constituents and 

 nitrogen) during the earlier years of forest growth, and 

 thus greatly improve in value. 



Adaptation of Manures to Crops. The true economy 

 of manure can be understood 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 



