CANE SUGAR. 



Among other plants grown in tropical countries as green manure are, 

 fieslania aegyptica, Crotallaria pincea and C. lalurmfolia , Phaseolus semierectus, 

 Arachis hypogaea (the earth nut), Soja hispida (the soy bean), Dolichos Idblab 

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

 x)f commerce), and, in Hawaii, a variety of lupine. 



The percentage of nitrogen in some of these plants is given below : 18 



Per cent. Per cent. 



Water. Nitrogen. 



Sesbania aegyptica 82*30 . . '68 



Crotallaria laburnifolia 79 -80 . . '70 



Phaseolus semierecttis 81*00 . - '52 



Arachis hypogaea Plant 80*00 . . -58 



Arachis hypogaea Fruit . . 2*76 



Rotations. Different crops have a predilection for different forms of 

 mineral matter, and thus remove from the soil very different amounts of the 

 different constituents of plant food, so much so that the ash of a crop may con- 

 sist in general of one predominant constituent ; by growing continually one 

 and the same crop on the same piece of land there is then a tendency to 

 exhaust one particular constituent. If, however, different crops be grown in 

 rotation, an element of plant food which was removed in large quantities in 

 one year is not absorbed to such an extent by the succeeding crop, and by the 

 time the crop first in rotation is planted a second time a sufficiency of the 

 particular material exhausted by this crop will have become available, due to 

 the natural process of disintegration which soils are continually undergoing. 

 As an example of such a rotation, the Norfolk system may be quoted ; this is 

 wheat, roots, barley, clover; the roots are consumers of potash, the wheat 

 takes up phosphates, the barley absorbs silica, and the clover feeds largely on 

 lime and magnesia. 



It is especially to be noted in this rotation that the wheat follows the 

 leguminous crop of clover ; wheat is a crop that responds to a supply of nitrogen 

 in this case in part provided by the root residues of the clover ; the cane, too, 

 demands, as is shown in the manurial trials quoted above, for its successful 

 growth a supply of readily available nitrogen, and in certain districts a 

 leguminous crop precedes the cane crop. 



Cane growing districts may be divided into those where the cane forms 

 the sole output of the soil, and those where it is alternated with other crops. 

 Into the first category fall the districts of Cuba, the Hawaiian Islands, British 

 Guiana, Trinidad, Fiji. In Java, Egypt and British India, a complete 

 rotation is practised, and in Louisiana and Mauritius the cane fields are 

 rotated with leguminous crops which are ploughed in. 



In Egypt, on the lands controlled by the Daria Sanieh, cane was grown 

 for two years, preceded by a year's fallow ; following on the cane crop corn arid 

 clover weie grown; the cane itself was not manured, with the object of 



86 



