98 



[August, 1911. 



GUMS, RESINS, SAPS AND EXUDATIONS. 



MANURING OP HEVBA RUBBER. 



(From Tropical Life, Vol. VII., 

 No. 5, May, 1911.) 



Although the application of manures 

 is a comparatively recent introduction 

 into rubber plantations, experiments 

 have already shown that their judicious 

 use is followed by good rdsults and im- 

 proved yields. It has been established 

 that when the soil is supplied with a 

 well-balanced plant-food the growth 

 and the vigour of the rubber trees are 

 considerably increased, rendering them 

 at the same time more capable of resist- 

 ing pests and injuries from other causes. 

 Properly manured young trees allow 

 tapping operations to be commenced six 

 to twelve months earlier, whilst simil- 

 arly treated old trees show a greater 

 increase in girth and renew their bark 

 more quickly and more thoroughly than 

 the trees grown on unmanured land. 

 Experiments ha\e further shown that 

 owing to the application of manures the 

 flow of latex was more vigorous, and 

 that the coagulation of rubber from this 

 latex took place more promptly. If, on 

 the other hand, it is bcrne in mind that 

 the fertility of the soil of a plantation 

 is reduced not only by the amount of 

 plant-food removed in the latex, but to 

 a much larger extent by the considerable 

 quantities of fertilizing ingredients 

 which are continuously required for the 

 renovation of the bark, for the growth 

 of new wood, and for the production of 

 leaves and fruit, it is obvious that 

 sooner or later even the richest soil 

 becomes exhausted unless adequately 

 manured. It therefore follows, in the 

 light of the above results, that it is to 

 the advantage of every planter to 

 prevent soil-exhaustion on his plant- 

 ation, and at the same time to encourage 

 increased yields of rubber. 



Unfortunately, on nearly every plant- 

 ation the production of farmyard 

 manure and compost, even if all the 

 waste is clearly collected, is insufficient 

 to meet the manurial requirements of 

 the plantation. Therefore, in order to 

 maintain or to increase the fertility of 

 the soil, the bulk of, if not all, planters 

 must avail themselves of the use of 

 artificial manures, especially as they 

 can be made up to any formula, and so 

 enable the owner or manager to apply 

 just those fertilizing ingredients that 

 are needed. 



Nitrogen in readily available form is 

 supplied by nitrate of soda, nitrate of 

 potash, nitrate of lime, sulphate of 



ammonia and calcium cyanamide or 

 nitrolim. Nitrate of soda, nitrate of 

 potash, and nitrate of lime contain 

 nitrogen in the form of nitric acid— which 

 is directly assimilable by the plants- 

 dissolve easily in water, and are not 

 absorbed by the soil. They should 

 therefore be applied in light dressings 

 only, in order to prevent their being 

 washed out of the soil. Nitrate of soda 

 contains 15'5 per cent, and nitrate of 

 lime 13 9 per cent, nitrogen. Nitrate of 

 potasjh contains 13"5 percent, nitrogen 

 and 44 per cent, potash, and should— 

 owing to this high percentage of potash- 

 only be used on soils which are deficient 

 in potash. Sulphate of ammonia and 

 calcium cyanamide contain 20 per cent, 

 and 18 per cent, nitrogen respectively, 

 but iu such a form that they must 

 undergo a change into nitric acid in the 

 soil before they become an available 

 plant food. In the Tropics, however, 

 this change takes place very speedily, so 

 that there is scarcely any difference 

 between the effectiveness, nitrogen for 

 nitrogen, of nitrate of soda, nitrate of 

 lime, sulphate of ammonia, and calcium 

 cyanamide. The choice.between these is 

 dictated more by the character of the 

 soil and the price of the fertilizers per 

 unit of nitrogen. Whereas calcium 

 cyanamide and nitrate of lime are suit- 

 able for all soils, though preferable for 

 those poor in lime, sulphate of ammonia 

 should only be used on soil well pro- 

 vided with lime. Nitrate of soda can be 

 profitably used on almost all soils, 

 excepting light saudy soils, but shows 

 its best effects on loamy soils. 



All these nitrogenous manures are 

 quick acting, and their nitrogen will be 

 absorbed by the rubber tree within a 

 short time* of their application. It will 

 therefore be advisable to meet the conti- 

 nuous requirements of the rubber tree in 

 nitrogen by applying a portion of what 

 is required by means of some less quickly 

 available manure, such as oil cake or 

 blood meal. 



The best-known phosphatic manures 

 are super-phosphates and Thomas' phos- 

 phate powder or basic slag. 



The manurial value of the superphos- 

 phates (ordinary and concentrated) de- 

 pends upon their content of phosphoric 

 acid soluble in water and in citrate of 

 ammonia solution. Whereas the percent- 



* The effect of an application of nitrate of 

 soda upon the flow of latex in Ceara trees was 

 manifested within 48 hours. ( See Hawaii 

 Bulletin, No. 16.) 



