THE MANURING OF THE CAXE 



97 



In certain quarters, notably in Mauritius, after land has been under 

 iegnminosae for a time, it is prepared for cane cultivation again by burning off 

 the green above-ground crop. This process would seem to destroy the very 

 benefits to obtain which the green mamu'e was planted. Planters who follow 

 this system claim as good a result as when the green crop is buried, and point 

 to the saving in expense. To obtain definite information as to this process 

 the writer once grew on small plots equal to ^-^ of an acre crops of the 

 Phassolns limatus and Stizolohium sp. The results calculated out to an acre 

 were as below. The crop in both cases was six months between planting 

 and harvesting, which was done when the seeds were ripe. 



It will be seen that about 80 per cent, of the manurial value of the crop 

 was contained in the green crop ; if this is burnt off the nitrogen is lost, but 

 the potash and phosphoric acid remain in a form readily available for the 

 coming crop of cane. The economy' of burning off the green crop and losing 

 the nitrogen is comparable with the practice of burning off trash ; in any 

 case there is obtained a large amount of mineral plant-food brought up from 

 the subsoil. The high nitrogen content of the bean straw, and the possi- 

 biUty of using this material as bedding for plantation stock, and thus both 

 conser\dng it and obtaining a pen manure rich in nitrogen, is worth}- of notice. 



Among other plants gro\Mi in tropical countries as green manure are 

 Sesbania cegyptiaca, Crotalaria juncea and C. lahurnifolia, Phaseolus semiercc- 

 tus, Arachis hypogcea (the earth nut), Soja hispida (the soy bean), Dolichos 

 lahlab (the bonavist bean), Phascolus mungo (woolly p^Tol), Indigo tindoria 

 (the indigo of commerce), and, in Hawaii, Italian lupines, the plant which 

 was used by the ancient Romans for the same purpose. 



De Sornay,^* who has made a most detailed study of green manuring 

 under tropical conditions, has given the following crop results obtained 

 experimentally in Mauritius : — 



Weight of Crop of Green ;Manures (De Sornay). 



Weight of Green Crop. Nitrogen in Green Crop. 

 Plant. lbs. per acre. lbs. per acre. 



Cow peas (yellow) 

 Cow peas (grey) 

 Jack bean* 

 Pois ^luscat (black) 

 Pois Muscat (white) 

 Pois Muscat (marbled) 

 Pois d'Achery 

 Pois amberiquef 



When grown between the rows or simultaneously with the cane, the 

 crop amounts to about one quarter that recorded above. 



*Canavalia eusifoimis. tPbaseoius helvolutus. 



H 



