274 



The Supplement to the Tropical Agriculturist 



at 2,000,1)00 per annum, worth probably 

 £3,000,000; they have now bern almost exter- 

 minated. Plant sanitation and preventive mea- 

 sures can, if invoked, do as much for the preser- 

 vation of cultivated plants, and with the know- 

 ledge we now possess it is improbable that any 

 disease could so seriously damage a big agricul- 

 tural industay as has been the case in the past. 



Distances Between Trees. 



The average number of trees per acre on 

 rubber estates in Malaya in 1908 was 168, or 16 

 feet by 16 feet apart ; the statistics for 1907 

 showed that on the 31st of that year the average 

 was 153, or 17 feet by 17 feet apart. This, for 

 many reasons, is an improvement. It is to be 

 regretted that the cultivation of rubber is too 

 young an industry to have sufficient experience 

 of old trees planted at different distan es apart 

 to judge of this important question. The 



REASONS AGAINST CLOSE PLANTING IN RUBBER 



— 12 ft. by 12 ft., or 302 per acre, or closer — are : 

 That it prevents the tree from growing with full 

 vigour and to the greatest possible size, forcing 

 it to run up to the light and giving it no room 

 for lateral branches. That it increases the cost 

 of collection of rubber, since a larger number of 

 trees have to be tapped for the same amount of 

 rubber. That if it is found necessary to give 

 the trees more room, the cutting out of a pro- 

 portion of them is fraught with much danger to 

 the remainder, inasmuch as each dead rubber 

 tree, root or portion of root, is a potential cen- 

 tre or root disease, and may harbour white auts. 

 That the spread of fungal and insect disease is 

 helped by the crowding together of the trees. 



ADVANTAGES CLAIMED FOR CLOSE PLANTING 



are : That it gives for the first years of tapping 

 a much larger yield of rubber. There is hot a 

 great amount of evidence on this point, but such 

 evidence as there is seems to point to it being 

 true that a larger yield of latex and of dry rubber 

 can be obtained at any rate in the first three or 

 four years of tapping. It is also claimed that 

 the closeness of the trees more quickly produces 

 shade over the ground and so prevents the growth 

 of weeds. The whole question of weeding is being 

 considered at the present time ; if it is believed 

 that to cover up the ground with a green manure 

 is the best method of cultivation, then the fact 

 that close planting reduces the cost of weeding 

 is of no value. That in order to compensate for 

 the casual losses of trees, which in the course of 

 time must necessarily occur, more trees should 

 be planted than are wanted. The answer to this 

 is that where trees are planted at large distances 

 30 or more feet apart, supplies come on with- 

 out difficulty, and it is only in crowded estates 

 that difficulty is found in replacing casualties. 

 To plant more rubber trees than it is inten- 

 ded to permanently keep on the estate, and 

 afterwards by cutting out to reduce the num- 

 ber, is a dangerous policy. No one acquainted 

 with diseases in plants would deny that to leave 

 the dead roots of trees of the same species in 

 close proximity to the roots of living trees is 

 most likely to encourage root fungus and insect 

 pests, while the cost of removing the roots, 

 even if the trees are cut out when quite young, 

 is prohibitive. If a planter finds it necessary 



to give more growing room — i.e., space for the 

 branches and leaves of some of his trees — it is 

 preferable to pollard some of the trees, and 

 allow them to grow slowly underneath the bran- 

 ches of the unpruned trees, rather than to leave 

 the decaying roots of dead rubber trees, which 

 he has cut down, dotted all over his fields. 



Cover Plants Instead of Clean Weeding. 



The question as to the relative advantages 

 of clean weeding and the use of cover plants 

 (the use of which has been advocated in my 

 annual reports for the last three years) is 

 gradually being seriously considered by the 

 practical planter, and many thousands of acres 

 of rubber, certainly not less than 15,000 are 

 now cultivated with various cover plants. It 

 needs but little observation of rubber clearings 

 to decide that an immense amount of top soil, 

 containing a large proportion of humus, has 

 been washed away from sloping land to the 

 detriment, both present and future, of the rub- 

 ber. An examination of the water in the drains 

 of flat land, which is dark coloured when the 

 clearing is first opened and gradually becomes 

 clearer when many tons of water have passed 

 through the soil, will show that this same pro- 

 cess of exhaustion of the soil is going on very 

 rapidly on clean weeded flat lands though not 

 to the same extent as on the hillsides. Most 

 practical planters have observed that the roots 

 of plants in the tropics grow more quickly and 

 vigorously when the earth where they are gro- 

 wing is shaded from the sun, and for this reason 

 the surface of nurseries is covered with a thatch 

 of grass or other convenient coyering. These 

 arguments seem in themselves sufficient to in- 

 duce a trial of cover plants ; but the additional 

 argument that the process of clean weeding is 

 continuous and the most costly of all the work 

 on a rubber ostate before it comes into bearing 

 should be a further reason for the adoption of the 

 system of cover plants. Various cover plants have 

 been used on acreages varying from 400 acres, 

 practically in all casus with successful results. 

 It is unfortunate for the increase in the belief in 

 this method of rubber cultivation that a large 

 number of the planters who tried cover plants did 

 so on the weediest and worst-drained parts of 

 their estates. It would be as fair to test a food, 

 which is recommended for supporting working 

 men, on emaciated and abnormal \y weak persons, 

 and when it did not produce the results hoped 

 for, deeming it a failure. Another reason for 

 some planters not finding the use of cover plants 

 so perfect a substitute for weeding as they hoped 

 was that the cover plant (very often crotalaria) 

 was sown broadcast, and it has been found by 

 experience over laige areas that this method of 

 planting cover plants is wasteful and very much 

 less effective than 



SOWING THE SEED BY DIBBLING, 



planting in furrows, or similar methods. The 

 loss may be due to the exposure of the germi- 

 nating seed to the sun, or to its being washed 

 along when the tender rootlets are beginning 

 to form, or birds may eat the seed ; but whatever 

 is the cause, it is always found that the propor- 

 tion of seed producing plants is very small 

 indeed. On the other hand, the planting in lines, 

 the seed being slightly covered, results in 80-100 



