64 



TROPICAL AGRICULTURE 



CHAP. 



Improve- 

 ments 

 wanted in 

 the tropics. 



Resting of 

 various 

 layers of 

 the soil. 



Mechanical 

 effect on 

 soils. 



Rotation 

 prevents 

 blights. 



the value of manures on his land, or the results of rotation on 

 his crops, &c. Indeed it is mainly by experiments, conducted 

 by scientific men and farmers or planters, that agriculture 

 has become what it is to-day. In the tropics there is much 

 room for improvement and discovery : and every planter, no 

 matter how humble may be his position, is capable of 

 making such discoveries by experiment as may be of 

 material benefit to his neighbours, and perhaps to the world 

 at large. Some of the most wonderful scientific discoveries 

 of all ages have been made by humble workers, without the 

 aid of any elaborate apparatus. 



An important effect of rotation is the resting of the 

 various layers of the soil. For instance, maize sends down 

 its roots deep into the ground, and so derives much of its 

 sustenance from the sub-soil. Potatoes and tanias, on the 

 other hand, are surface feeders, and they eat up the soluble 

 constituents of the surface soils, which were, to a great 

 extent, left alone by the roots of the maize. 



Rotation also exerts a beneficial, mechanical effect on the 

 soil in two ways. Firstly, in the preparation of the land 

 each year for the different crops, the turning over of the 

 soil causes its exposure to the atmosphere, and the dormant 

 constituents are thereby acted upon by the oxygen of the air, 

 with the result that the active and soluble constituents are 

 increased in quantity. Secondly, the roots of the former 

 crops, rotting in the soil, cause channels for the entrance of 

 water and air in all directions, and thus the soil is made 

 more porous, and the atmosphere is able to exert its bene- 

 ficial effects not only on the surface but even in the sub-soil. 



In addition to all these advantages, a proper system of 

 rotation prevents blights and keeps away destructive insects 

 that confine their depredations to particular plants. When 

 a crop intervenes on which these insects cannot feed they 

 die of starvation, and are in this way got rid of. The same 

 applies to vegetable blights, which are usually in the form of 

 extremely minute plants belonging to the order of moulds or 



