82 CHAPTER VI 



4. Soils yielding o-oo8 per cent, potash can be regarded as containing 

 under the usual system of cultivation sufficient available potash for the 

 needs of the sugar cane. 



5. If the potash lies betv/een 0-005 per cent, and o-oo8 per cent, it is 

 doubtful if the application of potash salts will result in remunerative returns. 



6. Where the potash falls below 0-005 per cent, it is advisable to add 

 potash salts in the manures. 



7. The demand of the sugar cane for lime as a plant food is low, and if 

 a soil gives up more than o-oo6 per cent, to the i per cent, citric acid solution, 

 it probably will 3neld sufficient for plant food for ordinary crops of sugar cane. 



Barbados. — Harrison and BovelP in a series of experiments, carried out 

 between 1885 and 1889 at Dodd's Reformatory in Barbados, came to the 

 general conclusions detailed below : — 



" I. The addition of readily available nitrogen to mineral manures produces 

 a large increase in the weights of cane grown, but excessive dressing (over 3 cwts. 

 sulphate of ammonia per acre) may cause a marked decrease in the richness and 

 putity of the juice. 



2. Under certain climatic conditions, manuring with nitrogen in form of 

 slowly decomposing organic matter may, if applied before or soon after the planting 

 of the canes, produce excellent results. Applications of such slow-acting manures 

 in June or July at the period of the sugar cane's fiost active growth are inadvisable, 

 and may result in considerable loss. 



3. Upon the soil, and under the climatic conditions existing at Dodds' during 

 the years 1885 to 1889, both inclusive, nitrate of soda was markedly inferior to 

 sulphate of ammonia as a source of nitrogen for sugar cane. 



4. The profitable employment of purely nitrogenous manures depends 

 largely upon the state of the soil. li the soil is in good heart, such applications 

 may realize heavy returns ; if poor such manurings will result in heavy loss. 



5. For the maximum return of sugar cane by manuring, phosphates must 

 be present in the manures used. 



6. If such phosphates are applied in the form of superphosphate of lime, 

 great care must be exercised in their use and application, as, whilst light dressings 

 of superphosphate capable of supplying 75 lbs. or 80 lbs. per acre of ' soluble 

 phosphate ' (equivalent to from 16 to 18 per cent, of ' soluble phosphates ' in 

 commercial sugar cane manures when applied at the rate of one ton to five acres) 

 may produce large increases in the weights of canes, &c., heavier dressings do 

 not produce corresponding increases, and excessive ones may even reduce the 

 produce below that obtained when manuring with nitrogen and potash only. 



7. The use of insoluble phosphates such as precipitated and mineral phosphates 

 is not advisable during the period of the cane's active growth, but may produce 

 excellent results when applied to the soil at an early period, in a very fine state of 

 subdivision in large quantities, and uniformly mixed with it. To obtain, however, 

 equally profitable results with these phosphates, as with moderate applications of 

 superphosphates, it is absolutely necessary that they be purchasable at far lower 

 prices than they can be at present obtained in Barbados. 



8. The addition of potash to manurings of phosphates and nitrogen produces 

 in all soils at all deficient in available potash large increases in the yield of cane 

 and of available sugar in the juice per acre. 



9. The most advantageous time for the application of potash-containing 

 manures appears to be at the earliest stages of the plant's growth, and pecuniarily 

 the use at this period of so-called early cane or potassic manures is far preferable 

 to that of even the highest quality of manures which were formerly used. 



10. The presence of an excess of potash in the manures does not injuriously 

 affect the purity of the juice, by increasing either the glucose or appreciably the 

 amount of potash salts contained in it. 



11. No definite information has been obtained with regard to the influence 

 of the mineral constituents of the sugar cane manures upon the saccharine richness 

 of the canes ; although, in the great majority of cases, canes receiving potassic 

 manures have been somewhat richer in sugar than those otherwise nianured. It 

 appears, therefore, probable that increased saccharine richness must be sought in 

 the cultivation of varieties, the careful selection of tops for planting from healthy 

 and vigorous canes (by this selection, whilst the saccharine strength of best canes 

 of a variety would not be increased, the average might be greatly raised), and possi- 

 bly by the seminal reproduction of carefully selected canes and varieties." 



