THE MANURING OF THE CANE 81 



cent., equal to 960 Ibs. of nitrogen per acre added to the soil to a depth of eight 

 inches. 



3. The growth of the sugar cane on plots receiving only nitrogenous manures 

 has resulted in losses of soil nitrogen : where sulphate of ammonia was applied, 

 the loss amounted to 14-7 per cent., or to 670 Ibs. of nitrogen, and, where nitrate 

 of soda was used, to 16-3 per cent., or to 775 Ibs. of nitrogen per acre, in the soil 

 to a depth of eight inches. 



4. On soils manured with phosphates, potash, and nitrogen in the form 

 of sulphate of ammonia, the loss of soil nitrogen in the top eight inches amounted 

 to 14* 7 per cent., or to 700 Ibs. per acre, while where nitrate of soda was the source 

 of nitrogen the loss was far higher, amounting to 26-5 percent., or to 1250 Ibs. 

 per acre. 



5. The soil in 1891, at the commencement of the experiments, yielded 0-0142 

 per cent, of phosphoric anhydride to a i per cent, aqueous solution of citric acid. 

 After ten years' cropping without manure it yielded 0-0086, which shows a loss of 

 nearly 40 per cent, of the probably available phosphoric anhydride, or of, in round 

 figures, 170 Ibs. per acre. 



6. Where the soil received manures not containing phosphates, the proportion 

 of probably available phosphoric anhydride was reduced to 0*0096 per cent., 

 equal to a loss of 32-4 per cent., or to one of, in round figures, 140 Ibs. per acre. 



7. Where superphosphates were used in addition to nitrogenous manures, 

 the proportion of probably available phosphoric anhydride was reduced to 0-132 

 per cent., indicating a loss of 7 per cent., or of 30 Ibs. per acre. 



8. Where slag-phosphates had been applied, the probably available phosphoric 

 anhydride has been reduced to 0-0102 per cent., equal to a loss of 28- 1 per cent., 

 01 to one of 120 Ibs. per acre. It is worthy of note that in our more recent experi- 

 ments, while manuring with slag-phosphates produced on the plots, which had 

 received superphosphates during the earlier years of the experiments, mean increases 

 of only 2-3 per cent., they produced on those which had been manured with slag- 

 phosphates a mean increase of 5-8 per cent. 



9. The determinations of potash soluble in i per cent, citric acid and in 

 2ooth normal hydrochloric acid showed that cultural operations have made probably 

 available more potash each year than is required for the growth of the sugar cane, 

 the original samples yielding potash at the rate of -262 Ibs. and 278 Ibs. per acre 

 to a depth of eight inches, those not manured with potash salts during ten years 

 at the rates of 376 Ibs. and 500 Ibs., and those which received potash salts in addition 

 to nitrogenous manures at the rates of 357 Ibs. and 530 Ibs. 



10. Judging from the solubility of the lime in the soil in 2ooth norma 

 hydrochloric acid, cultural operations set free in a soluble form more lime than the 

 crops utilized, the original soil yielding lime to the solvent at the rate of, in round 

 figures, 3400 Ibs. per acre to a depth of eight inches, while the samples taken after 

 ten years' cultivation yielded at the rate of 3800 Ibs. The soils which received in 

 July, 1891, slaked lime, supplying in round figures 6700 Ibs. lime per acre, yielded 

 to the acid in 1902 a mean of 5000 Ibs. per acre, thus indicating after ten years' 

 cultural operations a retention in the uppermost layer of the soil of only 1200 Ibs. of 

 added lime in a readily soluble form. 



11. The action of the lime on the solubility of the potash in the uppermost 

 layer of the soil appeared well marked, the samples from the not-limed land yielding 

 to 20oth normal hydrochloric acid at a mean rate of 460 Ibs. potash per acre to a 

 depth of eight inches, while those from the limed land yielded at the mean rate of 

 640 Ibs." 



Finally, as a result of these analyses and experiments, Harrison lays 

 down certain precise and formal propositions of the greatest value to the 

 agricultural chemist responsible for the economic manuring of large areas 

 of sugar cane. These may be summarized as under : 



1. Soils which yield 0-007 P er cent, phosphoric anhydride to i per cent, 

 aqueous citric acid with five hours' continuous shaking will not as a rule 

 respond to manurings with phosphates. 



2. Under similar conditions soils yielding 0-005 P er cent, to 0-007 P er 

 cent, will benefit as a rule by phosphatic manurings. 



3. It is advisable to apply heavy dressings of slag phosphates or lighter 

 ones of super or basic phosphates to soils yielding less than o 005 phosphoric 

 anhydride. 



