CANE SUGAR. 



5. Practically on all soils manurings with nitrogen require to be 

 supplemented by phosphoric acid. The most effective form appears to be 

 superphosphate of lime and slag phosphate meal. Mineral phosphates are of 

 distinctly lower Talue and are not effective unless applied in quantities far 

 exceeding in value those required for either superphosphate or slag phosphate 

 meal ; as a rule phosphates should only be applied to plant cane, their action 

 on ratoons being limited. 



6. On some soils the application of potash salts in quantities from. 60 to 

 160 Ibs. sulphate of potash per acre results in greatly increasing the effectiveness 

 of nitrogenous manuring. Soils containing less than '01 per cent, potash soluble 

 in 1 per cent, citric acid will as a rule respond favourably to this treatment, 

 while those containing between *01 per cent, and '02 per cent, may or may not 

 be favourably affected. 



Harrison 3 has also given a resume of the results obtained from twenty- 

 four years' experimental work in British Guiana. A short abstract of these 

 results is given below : 



Lime. Alternate beds of heavy clay land were treated with five tons of 

 slaked Barbados lime per acre. The canes were grown up to third ratoons and 

 then fallowed for a year. In the plots which were manured in addition to 

 liming, the total increase due to liming was 37'0 tons of cane per acre, and in 

 the unmanured plots at the rate of 33-7 tons per acre. Both the above 

 increases refer to the sum total of ten crops harvested in 13 years. 



Phosphates. Applications of phosphates have not always resulted in 

 financial benefit. It appears that the most satisfactory mode of using phos- 

 phates is to apply 3 cwt. of superphosphate or 56 cwt. of slag phosphate to 

 plant canes, the dressings of slag phosphate being more remunerative than 

 those of superphosphate of equal cost. Phosphates do not benefit ratoons and 

 Prof. Harrison thinks it doubtful if it is necessary to apply phosphates to 

 Demerara soils as often as once in five years. 



Potash. Results obtained with both sulphate and nitrate of potash 

 indicate that potash is not required on the heavy clay soils of British Guiana 

 under the conditions of ordinary agricultural practice. 



Nitrogen. As the mean result of ten crops of cane in 13 years it was 

 found that 10 Ibs. of nitrogen as sulphate of ammonia, when added in pro- 

 portions up to 300 Ibs. per acre, gave an extra return of 1-3 tons of cane per 

 acre, or 2 cwt. commercial sugar. With nitrate of soda up to 250 Ibs. per 

 acre, 10 Ibs. of nitrogen would probably give 1*4 tons of cane, equal to 2 cwt. 

 of commercial sugar, but experiments indicate that it is not wise to apply 

 more than 250 Ibs. nitrate of soda at one dressing. With dried blood the 

 indications over eight crops were that the relative value of nitrogen in this 

 material was 73 per cent, of that in sulphate of ammonia. 



56 



