THE MANURING OF THE CANE 



97 



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

 leguminosae 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 manure 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 ^-J-^ of an acre crops of the 

 Phaseolus lunatus and Stizolobium 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- 

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

 conserving it and obtaining a pen manure rich in nitrogen, is worthy of notice. 



Among other plants grown in tropical countries as green manure are 

 Sesbania cegyptiaca, Crotalaria juncea and C. laburnifolia, Phaseolus semierec- 

 tus, Arachis hypog&a (the earth nut), Soja hispida (the soy bean), Dolichos 

 lablab (the bonavist bean), Phaseolus mungo (woolly pyrol), Indigo tinctoria 

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

 was used by the ancient Romans for the same purpose. 



De Sornay, 24 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. Ibs. per acre. Ibs. per acre. 



Cow peas (yellow) 

 Cow peas (grey) 

 Jack bean* 

 Pois Muscat (black) 

 Pois Muscat (white) 

 Pois Muscat (marbled) 

 Pois d'Achery . . 

 Pois amberiquef 



50,200 

 51,000 

 28,000 

 42,000 



34.700 

 34.500 

 23,100 

 42,600 



190 

 219 



210 

 210 



I8 7 

 248 



33 

 226 



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

 crop amounts to about one quarter that recorded above. 



*Canavalia eusiformis. 



t Phaseolus helvolutus. 



H 



