The Preparation of Plantation Rubber

To criticise the methods of the pioneer planters of Hevea Brasiliensis presents no difficulty in the light of present comparative knowledge, and to be "wise after the event" is a failing which is not confined to those interested in modern planting methods. Looking at the matter broadly, however, it must be acknowledged that the pioneers, wrong though they may have been on some points, did remarkably well, considering that there existed no real knowledge on the subject and that the methods employed were perforce of an empirical nature.

Although we know a little more concerning the scientific aspects of rubber planting, the sum total of that knowledge does not justify any drastic criticism of the methods employed by our predecessors. In fact, although we may be of opinion that on general lines there is little now to be learned regarding the planting of Hevea Brasiliensis, our present knowledge does not preclude the possibility that future investigations may bring against us charges similar to those sometimes levelled at the earlier planters.

The main theme of the present volume is that of the preparation of rubber for the market. Hence it is not proposed to deal in detail with the work attaching to the opening and development of rubber estates. For this the reader is referred to the literature dealing specifically with rubber planting. Certain points in connection with planting may advantageously be treated in a general way according to modern knowledge, and of these it is proposed to discuss a few in the following pages.

Seeds, showing Variable Size, Shape, and Marking.

Seeds.-The view is now generally held that many areas were planted from seed which was not collected in a discriminate manner; and that probably the comparatively low yields obtained on areas of some estates may be due to the employment of seed from a poor strain. To be able to decide whether such explanation fits the case demands a full knowledge of all the possible factors governing the question of yields. It may, or may not, be a fact that seed from a poor strain is wholly or partially accountable for low yields; but whatever the degree in which the seed influences the result, it is an axiom that to obtain the best results in all planting industries a most judicious selection of seed should be made. In short, seed obtained from good-yielding specimens by selective treatment will eventually produce progeny of good-yielding strain.

Felling Light (Secondary) Jungle.

The recognition of these principles as applied to the planting of H. Brasiliensis has focussed recent attention upon the desirability of planting nurseries with seeds obtained from those trees which are known to be good producers of latex of normal consistency. It does not follow that the tree of most rapid growth and development is necessarily the best yielder; such is often not the case. In the matter of selection, therefore, one has to take other standards than that of size; and the issue is narrowed chiefly to a consideration of the yields of latex given by individual trees. It has been found by various experimenters that there is no necessity to proceed to such a refinement as the determination of the actual weight of rubber yielded. The dry rubber content of latices from the same trees is found to be so comparatively regular, allowing for climatic changes, that it is sufficient for the purposes of selection to measure the volumes of latex yielded by individual trees.

Seedling, showing Root-System with Seed

still Attached.

Unfortunately the industry is so young that the question of seed selection yet awaits study. The task presents certain practical difficulties, and would be by no means so easy to control as in the case of seed selection from other plants. It will be obvious that several generations of trees raised from selected seed would have to be under observation before any sound deductions could be made from statistics obtained in the course of the work. Thus the problem of seed-selection as it concerns the establishment of a high-yielding strain would involve many years of observation on the part of a trained man. Unfortunately neither the man nor the facilities for such experimental work exist at the present moment in the Federated Malay States. On the scientific side the industry is incommensurably staffed, and most of the workers' time is occupied with routine work connected with estate practice.

New Clearing.

In the middle distance, felled trees awaiting burning; in the foreground, a flat and wet area with main drainage outlined. (By courtesy of the manager of Membakut Estate, British North Borneo.)

Typical Young Clearing, Aged about Three Years, planted on Virgin Soil.

Original Jungle Timber slowly Rotting.

Selection.-It is possible, however, that the question of strain improvement will be solved in another manner than that of successive breeding from the seeds of high-yielding trees. Such investigatory work is now occupying the attention of scientific organisations in the East, and credit is due to the stations in Java which have begun experimental work in this direction. In brief, the scheme may be outlined as follows. Trees known to be uniformly good yielders are kept under observation, and the seeds gathered carefully. These seeds are germinated in a special nursery, and the best-grown seedlings are selected for further operations. At a certain stage a bud is taken from a high-yielding parent tree and grafted upon the stem of the seedling. When this has "struck" the original head of the seedling is removed. This ensures that one has in the seedling both the stem and future branch system of the same strain as the parent high-yielding trees. It is possible to go a step farther, and by certain processes induce a new root system to grow above the existing roots, which are then removed. One is then able to guarantee that the roots, stem, and branches will be of the original high-yielding strain. An objection sometimes made against the third operation of inducing a new root system is that the original tap-root is removed and that the subsequent system consists only of laterals. Against this argument may be quoted the observed fact that in actual development any one of the laterals may under such circumstances function eventually as a tap-root.

Light Jungle.

On the whole, this system of propagation receives the approval of investigators, and removes the objections which may be advanced against the development of a scheme entirely founded upon successive breedings from selected seed. The course of the investigations, also, are thereby shortened considerably. Care must be exercised in the work of obtaining and grafting the buds, but it has now been proved that by exercising reasonable precautions which are not beyond the intelligence and ability of subordinates, an extremely high percentage of success can be attained.

Dense Jungle.

Until such time as this process becomes practicable the inception of a planted area must follow the lines usually adopted.

Nurseries.-The usual practice is to obtain seeds from some estate which has a reputation for good yields and for exercising care in the gathering and shipping of seeds. The seed is planted in specially prepared beds, and the percentage of germination noted for future reference. The plants should be tended carefully, and close observation made for the detection of disease or pests. It is not uncommon to find that owing to lack of care in the preparation of the seed-bed, the young plants are attacked by disease.

Clearing Ready for Planting.

Surface timber removed, but stumps remaining.

Stumps.-At a stage, varying according to the requirements of the estate, when the plants are from twelve to eighteen months old, they are lifted from the earth. The roots and head are cut off, and the "stump" is ready for immediate planting in the field. Naturally any appreciable delay in planting, or unfavourable weather conditions, will militate against the chances of successful "striking"; and it is not uncommon to find that a certain number of "supplies" will be necessary.

Seed at Stake.-A method sometimes adopted is to put out seed in the field, in prepared holes which indicate the exact position of the future trees. Usually three seeds are placed in each hole, and if two or three germinate, the plant having the healthiest appearance is retained, and the others removed. The possible objections to this method of planting are obvious to those acquainted with field conditions, but in actual practice planting seed "at stake" has often proved highly successful. Naturally the results obtained must depend upon the selection of good seeds, the care exercised in the preparation of the "holes," weather conditions, and the discrimination exercised in the selection of the plants to be retained-apart from such disabilities as the depredations of rats and other pests.

Basket Plants.-Yet another and perhaps the most popular method at present is the germination and growth of seedlings in baskets specially constructed for the purpose. These plants are kept under observation until of the required age and growth. They are then conveyed to the field, and the baskets are planted in prepared holes. The baskets, being of vegetable material, are liable to be attacked by various diseases while in the nursery or after planting. It is considered advisable, therefore, to treat them by dipping into some disinfectant such as tar, or a mixture of tar and one of the common proprietary disinfectants. Otherwise a disease may be conveyed from the basket to the seedling.

Preparation for Planting.-There can be no other opinion than that ideally all land required for planting should be perfectly clear of timber of every description. After felling and burning, under ordinary conditions a certain amount of clearing is effected, but in actual practice this amounts to comparatively little. Big logs and stumps are left because the cost of clean clearing is judged to be prohibitive and non-economic. Surface timber is gradually cleared in the course of development, and usually large stumps are the last to be tackled. The objection to this procedure is really not strong, but unfortunately an important point is generally overlooked. Granted that most of the dreaded diseases travel beneath the surface of the ground by means of buried timber, it is plain that as far as stumps are concerned, the chief source of danger lies in the existence of the roots. If these were carefully exposed and removed, the isolated stumps would then not be such potential infection points. It follows from this argument that the importance of removing buried timber cannot be too strongly insisted upon. It is not uncommon to find that some years after the opening of an estate, and after surface timber has been removed, a large number of trees are affected with Fomes lignosus (formerly known as Fomes semitostus). Such cases are directly attributable to the existence of buried timber, and no local treatment will be successful unless the whole of the area is dug over carefully, and all pieces of timber removed.

New Clearing; Slopes "Holed" for Planting; Flat Area being Drained.

(By courtesy of manager, Membakut Estate, British North Borneo.)

Silt Catchment Trenches.-Granted the ultimate necessity of clean clearing, it becomes necessary to take some precautions to prevent loss of soil by "wash" in young areas planted on sloping land. An argument often used in extenuation of the practice of allowing large surface timber to remain until it becomes rotten is that it is an aid in preventing loss of soil by wash. Its removal necessitates the institution of some method of preventing "wash." The establishment of terraces on steep slopes tends to the achievement of the desired result, but this method is not extended to more moderate slopes where loss by wash is still considerable. It is the opinion of the writers and others that the general case calls for the institution of silt catchment trenches, which, as the name denotes, fulfil the duty of catching any surface soil and of retaining rainwater. These trenches are usually laid out on contour, and do not exceed a length of 20 feet. They are usually from 18 inches to 2 feet wide and deep, and are so arranged on the slope that they occupy overlapping positions. The actual number of trenches required will depend upon the angle of slope; the steeper the slope the greater the number required-i.e., the shorter will be the length of slope between any two trenches. Given a clean area, it is obvious that the momentum acquired by running water (and hence the amount of soil removed) on any one slope will depend upon the distance travelled. It is advisable, therefore, to place a larger proportion of the trenches on the upper part of the slope than on the lower, so as to guard against the breaking down of the trench system under an abnormal downpour of rain.

On land thus prepared the writer has seen areas successfully planted, which, under ordinary conditions, were condemned as being too steep for planting. It is true that these trenches necessitate continual upkeep until the soil becomes well shaded by trees, but the actual amount of work demanded in cleaning and maintaining the trenches will depend largely upon the thoroughness with which the original work was planned and executed. Whatever may be the weaknesses exposed as a result of providing an insufficient number of trenches of inadequate dimensions, there can be no question that they are a necessity.

* * *