55 



during long periods of forest growth or of fallowing, while the 

 land is covered by dense growth of sedges, grasses and leguminous 

 plants, suffers great and rapid losses when the soil is put under 

 intensive sugar cane cultivation, and it is to the loss of the accu- 

 milated stores of readily available nitrogen that the marked falling 

 off in the yield of canes per acre which is almost invariably 

 noticed when successive crops are taken off from either new or 

 from long rested soils is due. This loss is greatly diminished 

 where very heavy dressings of farm-yard or pen manure are re- 

 gularly used and upon very heavy clay soils the loss may be re- 

 duced to a minimum and an actual gain ensue. The loss is greater 

 on soils manured with nitrate of soda, than when sulphate of am- 

 monia is used ; and is greater on limed, than on not-limed soils. 



Whilst there was a loss of phosphoric acid, it appeared that 

 cultural operations have made probably available more potash, 

 and more lime, each year than is required for the growth of the 

 sugar cane. 



The following are the general deductions arrived at during 

 these experiments : — 



(1) Nitrogen in the form of sulphate of ammonia, of nitrate of 

 soda, or raw guano, and of dried blood exerted a favourable 

 influence upon the yield of the sugar-cane, and is themanurial con- 

 stituent which mainly governs the yield of the plant. 



(2) Dressings of from 2 to 3 cwt. of sulphate of ammonia per 

 acre appear to be the most certainly profitable applications of 

 nitrogen. 



(3) The application of superphosphate of lime to plant-canes 

 may give increased yields when added to manurings of nitrogen 

 and potash, but ratoons should be manured with nitrogen only. 



(4) Slag phosphate is preferable to superphosphate of lime, but 

 the use of basic superphosphate is promising. 



(5) The effect of lime, chiefly mechanical, in improving the 

 texture of the soil, may be obtained perhaps at a lower cost by 

 using light ploughs or other cultivators. 



(6) The addition of phosphoric acid, of potash, or of lime, does 

 not affect the sugar contents of the juice of canes. The effects of 

 nitrogen retards ripening, and thus the juice is not so rich in sac- 

 charose as is that of canes grown without manure. But this is 

 more than offset by the larger yield of produce. 



(7) Mineral phosphates to give increased yields must be applied 

 to the soil in such heavy dressings as to render their use un- 

 profitable. 



(8) The addition of potash exerts little or no effect. 



The normal weathering of the constituents of the soil while 

 under good tillage sets free for each crop potash in excess of the 

 quantity necessary for the requirements for the plants. This 

 holds good under the conditions existent in British Guiana where 



