20 TROPICAL AGRICULTURE 



satisfactory growth of crops than is the case with the common 

 soils of temperate climates. 



It is a peculiar fact that on tropical islands in the trade-wind 

 belt drainage is a difficult matter on the lee side, while little 

 or no attention need be given to drainage on the windward side 

 of the island. The heavy laterite soils on the lee side of the 

 Hawaiian Islands require extremely deep plowing, the addi- 

 tion of green manures, and sometimes the use of dynamite and 

 other treatment in order to provide suitable drainage for mois- 

 ture movement and for the process of aeration. On the wind- 

 ward side of the same island, however, under a much greater 

 rainfall there are commonly few running streams and appa- 

 rently almost no superficial runoflE of water. In some farming 

 sections of the windward side of the island of Hawaii, water 

 for household use must be obtained from rain water caught 

 from the roofs of buildings, although the rainfall for months 

 at a time may average an inch a day. This water passes 

 through the soil and on into the porous lava rocks underneath, 

 furnishing no running streams or standing water. 



The use of dynamite in improving the drainage conditions 

 and tilth of soil has been adopted in a number of tropical 

 countries. The object in using dynamite in the Tropics is not 

 always precisely the same as that which prevails in cold cli- 

 mates where a distinct subsoil or hardpan may underlie the 

 arable soil. In the laterite soils of the Tropics there is little 

 or no distinction between soil and subsoil, the only apparent 

 change being one of color in passing from the top layer to a 

 depth of four or five feet. Since, however, these soils pack 

 very firmly during the long intervals between plowing, it is 

 obvious that some method of providing better subdrainage is 

 necessary. This perhaps has been accomplished in many in- 

 stances by the use of dynamite. The best results have been 

 obtained by exploding sticks of low-grade dynamite at a depth 

 of 3J^ to 4 feet and at distances of lo to 20 feet apart both 

 ways. The effect of the dynamite is to form cracks and crev- 



