93 CHAPTER VI 



The hypothesis of Loew, though carefully elaborated, is not accepted by 

 many agronomists ; it has been followed up chiefly in Japan by Aso and 

 others. The lime-magnesia ratio must apply to the soil water or to readily 

 soluble forms in the soil ; a hydrochloric acid soil extract showing an excess 

 of magnesia over hme would not be sufficient to condemn a soil on Loew's 

 hypothesis. It is of interest to note that in some Demerara soil waters 

 Harrison!* has found that with sulphate of ammonia manuring, the molecular 

 ratio of calcium-magnesium was i : 0-77 ; with nitrate of soda manuring 

 it was I : 1-52, and with no manuring i : 2-40, and with no cultivation 

 I : 2-57. 



Yields of cane had become very deficient in the second and third cases, 

 but Harrison does not commit himself to attach any special significance to 

 these ratios. 



Effect of Manuring on the Composition of the Cane. — There is a wide-spread 

 behef that heavy manuring adversely affects the quality of the juice of the 

 cane, and under certain conditions this may be correct ; thus in a district 

 such as Demerara, where a short period of growth obtains, a late manuring 

 results in an impure juice. Possibly in such a case not only is the maturity 

 of the crop delayed, but a second growth of young cane is stimulated and the 

 comparison may become one of mature and of immature cane. Again, with 

 heavy manuring, there is a consequent increase in the size of the crop with 

 less access of direct sunshine, and a delayed ripening is the result. 



That judicious heavy manuring has no harmful effect is shown from the 

 results regularly obtained in Hawaii ; nowhere is a sweeter and purer juice 

 obtained, and nowhere is the manuring more intense. Here, however, 

 owing to climatic conditions peculiarly favourable, a great part of the harvest 

 consists of fully matured cane cut at the period of maximum sweetness. 



Actual experiments on this point lead to somewhat contradictory results. 

 Thus Eckart^ found in Hawaii with unmanured cane a sucrose content in the 

 juice of 18 • 26 and purity of 90 • 69, manured canes affording a juice containing 

 from 16-40 per cent, to 17-85 per cent, sucrose, and of purity 89-16 to 90-60 

 Conversely, however, the same authority has supplied data of an experiment 

 where, in three instances, an application of 1,200 lbs. of high grade mixed 

 fertihzer and 300 lbs. of nitrate per acre not only enormously increased 

 the yield, but gave a sweeter and purer juice. 



Of the specific effect of manures, many ideas, supported or not by experi- 

 ment, may be met with. Lime is credited with producing a sweet and pure 

 juice in the West Indian adage : " The more lime in the field the less in the 

 factory," and this idea is reflected in the quotations in Chapter V. 



Phosphates are also believed to affect beneficially the sugar content of 

 the cane, and potash is reputed to have the reverse effect ; Harrison's ex- 

 periments already quoted fail however to countenance this idea. 



There is a certain amount of evidence that canes heavily manured with 

 readily available nitrogen are more susceptible to fungus attacks than are 

 others ; this may be due to the production of a soft-rinded cane due to rapid 

 growth, and possibly in the presence of infected soil or material the nitro- 

 genous matter may also benefit the development of the fungus. In Egypt, 

 it may be mentioned, on lands controlled by the Daria Sanieh manuring of 

 cane was not allowed. 



On the whole, the writer thinks that the bulk of the evidence points to 

 weight of cane only as being affected ; differences which may from time to 



