66 MANUAL FOR SUGAR GROWERS. 



in no way interfere with the growth of the latter. 

 When the green crop has grown as long as is con- 

 sidered prudent, it is cut down or pulled up and 

 buried in the banks by the weeding gangs, who find 

 very little difficulty in accomplishing this. By work- 

 ing in this manner even very stiff clay soils may be 

 got into good condition in a comparatively short 

 space of time. This method of working can only be 

 followed advantageously in a moist season ; in a 

 dry season the double crop appears to remove too 

 much moisture, and the cane crop suffers. 



In some places seaweed can be readily obtained. 

 This forms a valuable manure when ploughed in ; 

 by this means nitrogen and potash are supplied 

 together with vegetable matter. About twenty or 

 thirty tons per acre form an excellent dressing. 



Now as pen manure and green dressings merely 

 return to the soil for the most part potash and phos- 

 phates, etc., derived from the land itself, it follows that 

 as the exported crops carry away certain quantities of 

 various substances forming plant-food the land must 

 be rendered less fertile from year to year, so far as 

 mineral matters are concerned ; hence it is imper- 

 ative that manures supplying potash, phosphates, 

 etc., be imported if fertility is to be maintained. 

 Farm-yard manure alone is insufficient to maintain 

 fertility. 



The following brief sketch of some artificial or 

 chemical manures may prove of interest. 



Potash Manures. Formerly potash salts were ob- 

 tained entirely from the ashes of plants : in coun- 

 tries where forests prevail, as in North America, 



