MANUAL FOR SUGAR GROWERS. 33 



ment. Chemical manures will only exert a full and 

 beneficial action on soils already in good condition, 

 but which are deficient in some one or more sub- 

 stances constituting plant-food ; and of these, phos- 

 phoric acid, potash, and nitrogen are those usually 

 deficient, and which it is the function of the ordi- 

 nary chemical manure or fertilizer to supply. The 

 necessity for supplying other ingredients, such as 

 lime, magnesia, iron, etc., is sometimes pointed to by 

 special investigations, when the defect must be 

 remedied. 



Drainage. — Wlien a heavy shower of rain falls, a 

 certain quantity of water sinks into the gTOund, and 

 when the soil becomes saturated — if the fall is more 

 rapid than the absorption — a certain quantity flows 

 over the surface and is carried away by the ditches 

 and streams. If the rainfall continue for some 

 time, the soil becomes entirely saturated, the water 

 occupying the space previously occupied by air. 

 Now, it has already been shown that this condition 

 is highly unfavorable to the growth of such a crop 

 as the sugar-cane, which, as with most other crops, 

 requires a soil containing both air and moisture. It 

 is necessary, then, that the excess of moisture be re- 

 moved. Some porous soils are so situated that 

 when the rain ceases they naturally part Avith their 

 excess of moisture with sufficient rapidity to permit 

 the entrance of the necessary air ; such soils are said 

 to possess natural drainage, and merely require 

 attention to be directed to the channels for the es- 

 cape of the surface water ; such soils, however, 

 are not common. Other soils retain water for too 

 3 



