75 



These samples do not vary in composition to as great an extent as 

 might be expected, when it is considered that the soils in which these 

 canes were grown are of widely different chemical composition, especially 

 as regards their content of potash. Since no data are at present available 

 as to the ash of the entire cane, which may vary decidedly from that 

 of the bagasse, it is impossible to calculate even approximately the 

 amount of mineral matter taken from the soil by the Negros cane. 



Deer^i quotes from Stubbs, who, from experiments covering a period of ten 

 years, calculates the amount in pounds of mineral matter removed per ton of 

 the Lousiana Purple cane as follows: 



Nitrogen ^-^^ 



Phosphoric acid l-"*' 



Potash : 2.52 



Lime 2.54 



Expressed in kilograms per metric ton of cane, these figures would correspond to : 



Nitrogen ^•^'^ 



Phosphoric acid 0.73 



Potash 1-12 



Lime 



1.13 



Assuming a crop of 6 metric tons or 95 piculs of sugar, a little over twice 

 the present average in Negros, which would correspond roughly to 60 metric tons 

 of cane, there would be removed from the soil annually in kilograms per hectare 

 of land the following amounts of mineral matter : 



Nitrogen '^-^ 



Phosphoric acid '^^•° 



Potash 67.2 



Lime ^'^•^ 



Now, in 1 hectare of land, from the surface to a depth of 20 centimeters, or the 

 average depth to which the cane roots penetrate, there are 2,000 cubic meters of 

 soil of an approximate apparent specific gravity of 1.5, or 3,000,000 kilos. One- 

 hundredth of 1 per cent of this, the smallest difference which can be detected by an 

 accurate chemical analysis, would amount to 300 kilograms of any one element, 

 so it may be readily seen that at least five, and more probably ten, years would 

 be required before any depletion of the soil from successive crops of sugar cane 

 would be suggested by chemical analyses, even if absolute accuracy in sampling 

 and in analytic methods were assmned, not to mention the greater changes 

 which might be brought about during such a long period of time by mineral 

 matter carried up from greater depths by the soil water, or carried away by rains. 



These figures make no pretense at even moderate accuracy, but serve 

 to illustrate the relatively small order of magnitude of changes in the 

 composition of a soil which may be brought about by the cultivation 

 of sugar cane. It is likewise apparent that the ordinary commercial 

 fertilizers would need to be used in quantities of many tons to the 



" Loc. cit. 



