50 



TROPICAL AGl^ 



ICULTURl': 

 » 



Fertility to 

 be restored 

 by rest, as 

 well as by 

 good culti- 

 vation. 



fault lies with the trees, or that the soil is not adapted to 

 the cultivation, whereas the fault is entirely his own, as he 

 has gone on taking away from the soil without putting 

 anything back. 



Exhaustion may, in certain instances, be partly prevented 

 by 7'cst and by p7-opc7- cultivation. As, for instance, when the 

 land is dug or ploughed up in order that the dormant con- 

 stituents may be made active ; or when the cropping is 

 stopped by allowing the field to remain fallow. But this can 

 be done only in those cases where cultivation such as sugar 

 cane or corn is carried on ; for cacao and coffee, and other 

 such plants, are practically permanent, and so the land 

 cannot be fallowed, and the crops cannot be stopped. It is 

 in these cases, then, that manure and tillage operations are 

 so useful and necessary. 



The Action of Manures. — The principal action of 

 manures is to restore the fertility of an exhausted soil ; to 

 enrich a naturally poor soil ; or to prevent exhaustion by 

 giving back to the soil, in a suitable form, the various 

 elements taken away in the valuable crops. Besides the 

 action of adding plant food to the land, manures act 

 chemically on the organic and inorganic constituents of 

 the soil ; they render some of the dormant substances active, 

 and in this way they liberate plant food that was, as it were, 

 locked up in the land. A third, and an important action, is 

 a mechanical one., for manures improve the physical con- 

 dition of the soil by making tenacious and heavy clay land 

 lighter and more porous, and by binding together sandy 

 soils and making them more capable of retaining moisture. 



General and Special Manures. — Manures are usu- 

 ally divided into these two classes. A general manu7'e is 

 one that supplies to the soil all the consituents removed by 



General growing plants, not only from the soil but from the air. 



manures the j|- contains, therefore, all the organic and inorganic elements 



most valu- ' ' ° 111 



able. found in the plant ; and it is the most valuable kmd of 



Chemical 

 action of 

 manures. 



Mechanical 

 action. 



