Gums, Resins, 



202 



[September, 1909. 



This shows that the trees of plot O 

 were of more vigorous growth owing to 

 the washings received from the upper 

 plots. 



This fact, although it vitiates the trial 

 to a great extent, gives it added interest 

 if we compare with O, the results 

 obtained from plot NEK, for whilst O 

 has more than kept pace with NP and N, 

 it has not done so with NPK, 40 trees of 

 NPK gaining 175 centimetres in the 

 four months, while the 40 trees of O 

 only gained 154*25. 



How is that O, which gained by the 

 wash at the expense of NP and N, failed 

 to gain at the expense of NPK ? 



To my mind, the ressult shows plainly 

 that the failure of plot O to gain on 

 NPK is solely due to the presence of 

 potash in NPK, for whilst both nitrates 

 and phosphoric acid are subject to be 

 carried away in solution in the wash, 

 this is not the case, %t least to the same 

 extent, with potash which is energeti- 

 cally retained by clay, and thus it only 

 benefits the trees to which it is applied. 



If, now, we compare the plots NPK 

 and NP, we find that these two plots 

 started almost exactly at the same stage 

 of growth — the plot NP had, in fact, a 

 slight advantage of 2 centimetres '25 at 

 the start, NPK measuring 624025. to 

 NP 620C-50. 



We may say, therefore, that the two 

 plots started on January 31 with ab- 

 solutely even chances. Yet, four months 

 after we find that NPK has gained 175 

 centimetres on 40 trees, while NP has 

 gained 14P25 centimetres on 40 trees. 

 In 4 months each tree of 



N has gained 3'53 =per year 10-59 or 4£ in, 



NEK „ 4-37 = ,, 1311 or 5J „ 



which means to say that, assuming the 

 manures to continue acting at the same 

 rate till the end of the year, the com- 

 plete manure (nitrogen — phosphoric acid 

 and potash) will bring to each tree one 

 inch more of girth than the nitro-phos- 

 phatic manure without the potash. 



The improvement in growth brought 

 about by the application of nitrogen 

 only to plot N has been only slight, i.e., 

 100*75 centimetres in the four months on 

 the 40 trees- This shows a yearly in- 

 crease (over and above the normal increase 

 of girth before manuring) of half an inch, 

 which is not wholly negligable, but 

 considering the cost of nitrogenous 

 manures, it is doubtful whether a 

 purely nitrogenous application is pro- 

 fitable, apart from the fact that such 

 a one-sided application exhausts the 

 reserves of other constituents in the 

 soil, thus tending to retard growth 

 later on. 



As I have already stated, the plot O 

 started with too great an advantage to 

 make the comparison with NPK quite 

 fair. Y"et we find that at the end of the 

 four months Plot O grew from 648 to 

 802C-25 gaining 1540*25. Plot NPK grew 

 from 624*25 to 799 25 gaining 175C, a gain 

 of 20C*75 which will be found to work 

 out at 9/16 of an inch yearly. 



But we can get at a truer estimate of 

 the effect of the full manure by comparing 

 the rate of growth of the trees of 

 the same plot NPK before and after 

 manuring. 



The 2-year old 40 trees of NPK grew 

 from 624C*25 Avhich shows a yearly 

 growth of 3 is inch to 799*25 which shows 

 a yearly growth of 5| inch. Each tree, 

 at this rate, would therefore gain, by 

 manuring with a complete manure, 2.'^ 

 of an inch in one year, over and above 

 the normal rate of increase of the trees 

 without manure. 



To put it otherwise, if we assume the 

 tappable stage of a tree to be reached 

 when a tree has attained a girth of 20 

 inches, a tree manured with a complete 

 manure would be tappable at the age of 

 4 years, while the same tree, unmanured, 

 would only be tappable after its 6th year. 



These conclusions apply of course to 

 the present case, and they are liable to 

 vary with variation of soils and other 

 factors. 



The one fact which it is important to 

 show is that a complete manure in- 

 creases girth, and, therefore, quickens 

 the growth of wood and bark, and the 

 inference to be drawn from this is, since 

 the elaboration of the latex depends on 

 the formation of new ducts in the 

 renewed bark tissue (already tapped)— 

 that the production of latex itself must 

 be quickneed. This, however, is too big 

 a question to be settled by inferences, 

 and I hope to be able later on to give a 

 more tangible demonstration of the fact. 



Sheet A, 



Mb. F. M. Elliot's Rubber Planta- 

 tion, Holland Road, Singapore. 



Girths of 160 trees. 

 2 years old ou 31st January, 1909. 



Plot. O. 



Plot, N.P.K. 



Plot.N. P. Plot.N 



40 Trees. 



40 Trees. 



40 Trees. 



40 Trees. 



21* 



18* 



17- 



12-50 



20*50 



18' 



17*50 



12*50 



23* 



19*50 



10*50 



16*25 



16*50 



20* 



16-25 



11*25 



19* 



18*50 



17*25 



12- 



14*50 



15* 



17- 



14*50 



10* 



9* 



9 '50 



15' 



9*50 



9*50 



18* 



10*50 



13*75 



15* 



14* 



15- 



14-50 



10*50 



13- 



24- 



