August, 1911.] 



99 



Saps and Exudations. 



age of water-soluble phosphoric acid 

 ranges from 12 to 20 per cent, in ordinary 

 superphosphates, the concentrated super- 

 phosphates contain 40 to 43 per cent, 

 water-soluble phosphoric acid, and 2 to 3 

 per cent, phosphoric acid soluble in 

 citrate of ammonia solution. 



If superphosphate is applied to the 

 soil, its phosphoric acid, being soluble in 

 water, becomes disseminated thioughout 

 the soil, and is there absorbed by other 

 soil constituents, as lime, magnesia, iron, 

 and alumina, forming phosphates which 

 are insoluble in water. In soils contain- 

 ing a fair amount of lime the water- 

 soluble phosphoric acid is precipitated 

 into phosphate of lime, which supplies 

 the plants with available phosphoric 

 acid ; but on soils poor in lime, the water- 

 soluble phosphoric acid is either subject 

 to being washed out of the surface soil, 

 or is absorbed by the oxides of iron and 

 alumina forming compounds, the phos- 

 phoric acid of which the plants can only 

 assimilate with the greatest difficulty. 

 The use of superphosphates should there- 

 fore be limited to soils which are not 

 deficient in lime ; on these, 1 lb. of phos- 

 phoric acid in ordinary superphosphates 

 has the same effect as 1 lb. of phosphoric 

 acid in concentrated superphosphate. 



Thomas' phosphate powder, a by-pro- 

 duct in the manufacture of 3teel tree 

 from phosphorus, contains 15 to 20 per 

 cent, phosphoric acid, 40 to 50 per cent, 

 lime, and 4 to 5 per cent, magnesia. The 

 phosphoric acid in Thomas' phosphate 

 powder, although insoluble in water, is 

 easily soluble in weak acids, and there- 

 fore readily assimilated by plants. In 

 genuine Thomas' phosphate powder 80 

 per cent, and more of its phosphoric acid 

 is soluble in a 2 per cent, citric acid 

 solution, which portion is considered 

 quite as available as the water-soluble 

 phosphoric acid in super-phosphate. As 

 the phosphoric acid in Thomas' phos- 

 phate powder does not undergo any 

 changes in the soil which might reduce 

 its availability, the use of this phosphatic 

 fertilizer is not restricted to any parti- 

 cular class of soil, but can be applied 

 with advantage to all soils. Its effects 

 are most marked on soils deficient in 

 lime, and on soil containing an excessive 

 quantity of organic matter, in which 

 cases the effects of the Thomas' phos- 

 phate powder are due not only to the 

 phosphoric acid but also to the lime it 

 contains. The latter can be easily assi- 

 milated by plants, and, like every other 

 form of alkaline lime, improves the 

 mechanical condition of the soil, pro- 

 motes the oxidation of the nitrogenous 

 reserves, brings the soil potash in solu- 



tion, and helps to neutralize and render 

 harmless the organic acids of soils rich 

 in humus. 



The principal potash manures in use 

 are sulphate of potash and muriate of 

 potash. The former, containing 48 to 

 52 per cent, potash is especially recom- 

 mended for soils deficient in lime, where- 

 as the use of muriate of potash, contain- 

 ing 50 to 59 per cent, potash is better 

 limited to soils containing an ample 

 supply of lime. The sulphate of potash, 

 being less soluble than the muriate of 

 potash, is better retained by the soil, 

 and in very wet districts, although a little 

 dearer, is a more profitable source of 

 potash than muriate of potash. 



If the soil of the plantation is so poor 

 in lime that this deficiency cannot be 

 made good by the continued use of 

 Thomas' phosphate powder as phos- 

 phatic manure, the application of burnt 

 lime or ground lime-stone becomes 

 necessary. 



As to the quantities of fertilizing in- 

 gredients to be applied to rubber plant- 

 ations, this depends not only upon the 

 different requirements of the rubber 

 trees at their various ages, but also 

 upon the condition of the soil. For 

 plantations on fair average soils, show- 

 ing neither a marked excess nor a 

 marked deficiency in either of the three 

 fertilizing ingredients— nitrogen, phos- 

 phoric acid, and potash — the supply of 

 plant-food may be considered as well 

 balanced if these fertilizing ingredients 

 are applied in the proportion of 1 part 

 nitrogen, 1 to 1'5 parts phosphoric acid, 

 and 1*5 to 2 parts potash ; and, therefore, 

 for trees old enough to be tapped, which 

 require about 40 lb. nitrogen, 60 lb. 

 phosphoric acid, and 70 lb. potash per 

 acre, the following mixture may be 

 safely recommended to ensure good 

 results : — 



Ijjf cwt. nitrate of soda (or l£ cwt. sul- 

 phate of ammonia). 

 H cwt. oil cake. 



3j cwt. Thomas' phosphate powder 

 (or li cwt. concentrated superphos- 

 phate). 



1| cwt. muriate of potash. 



All these manures may be mixed to- 

 gether, with the exception of Thomas' 

 phosphate powder and sulphate of 

 ammonia. 



Where, however, plantations are laid 

 out on poor soils, the above quantities 

 should be increased by one-half ; and a 

 similar increase is advisable as regards 

 the potash supply on light soils, whereas 

 on strong soils— which rule, 



