26 CHAPTER III 



INFLUENCE OF CLIMATE ON MAURITIUS CANE CROP (WALTER). 



The question is, however, more complicated than this, and is controlled 

 by other factors, which are also discussed by Walter. The effect of rain 

 or drought in one year may continue into the next, and there is also a ten- 

 dency for small crops to follow heavy ones. This is not so much a question 

 of temporary soil exhaustion as that a large crop means a long period for 

 harvest, with a reduction in the time available for the next growing season, 

 when the crop consists mainly of ratoons. 



Other observations on record are those of Rawson 1 in Barbados, who, 

 from a study of rainfall statistics, showed that it was possible to foretell 

 the return of sugar per acre within an error of 6*6 per cent., when the rainfall 

 for the preceding twelve months was known. Similarly, Maxwell Hall 

 in Jamaica observed relative productions per acre of 14*41 and 15-59 as 

 corresponding to rainfalls of 56 and 76 inches respectively. 



It would not be unreasonable to suppose that those areas lying in a zone 

 of nearly constant rainfall would afford a cane of low sugar content. Such, 

 however, is not the case. The average precipitation on seven plantations 

 in the Hilo rain zone is 173 inches ; that on six plantations adjacent to, but 

 outside the zone, is 84 inches. Averaged over ten years the sugar content 

 of the cane grown on plantations in this rain zone was 13*05 per cent., that 

 of the plantations in the comparatively dry area being 13*22 per cent. The soil 

 conditions and varieties of cane grown were nearly identical, and at the 

 same time the drainage was very rapid. 



On the other hand, the effect of heavy rains during the crop season is 

 seen in a diluted juice for several days after the fall. If there is no decrease 

 in the purity, no loss of sugar but only a dilution is indicated ; a new growth 

 starting will cause the consumption of sugar in metabolic processes. 



Connected with the question of heavy rainfall is the possibility of larger 

 quantities of combined nitrogen being afforded to the crop. The most 

 detailed statistics on this matter are those of Lawes and Gilbert made at 

 Rothamsted in England, where they found on an average 4-92 Ibs. of com- 

 bined nitrogen in the yearly precipitation. Elsewhere most varied results 

 have been found. The greatest quantity of nitrogen as ammonia recorded 

 in a year has been found in Venezuela 16 and in Tonkin 17 , where 14*05 and 

 13 -60 Ibs. nitrogen respectively have been observed. The greatest quantity 

 of nitric nitrogen recorded was also in Tonkin and equalled 14*70 Ibs. nitrogen 



