Lrums, Resins, 



212 



[March, 1909- 



for by the advantage of keeping the 

 soil from the sun and rain. The girths 

 of young rubber trees grown with 

 tapioca is in many cases as large as those 

 of trees in similar land, clean weeded, 

 and without any other crops. 



The position thus is : Clean weeding is 

 a costly process, which ensures quick 

 growth of young rubber trees and pre- 

 vents the land being taken possession of 

 by undesirable weeds. On undulating 

 land it causes loss of top soil, and on all 

 land it means loss of moisture in the 

 surface layers of the soil. 



Rubber plants usually grow better in 

 clean than in weed-covered land, because 

 the plant-food and water present in the 

 soil is all available for the rubber and is 

 not used by the roots of various other 

 plants which are useless to the planter. 



The high cost of weeding and the fact 

 that, Avith a not too abundant supply of 

 labour, the majority of coolies are 

 employed at this work, both point to 

 the desirability of some other method 

 not less helpful to the growth of young 

 rubber, if such can be found. 



Though figures of cost of weeding vary 

 very greatly, on some estates the cost 

 two years after the land has been 

 opened is not under §2 per acre per 

 month, or $24 per year. This represents 

 on an estate of 1,000 acres a cost of 

 $24,000 per year, and a probable cost for 

 weeding of nearly $100,000 before the 

 rubber is in bearing. 



In labour it represents a continual 

 force of about 250 coolies working for 

 300 days in the year. 



I have for the last three years been 

 investigating the question of a substi- 

 tute for weeds which will reduce the 

 wage bill without reducing the rapidity 

 with which the rubber trees grow, and 

 mentioned in my annual report for last 

 year three plants which observation and 

 experiment show to be suitable and 

 therefore worth a serious trial on every 

 estate. 



These three plants belong to the order 

 Leguminosae, the clover, pea and crota- 

 loria tribe, a group of plants many of 

 which are characterised by the posses- 

 sion of bacteria on their roots. These 

 bacteria, the life history of which has 

 been investigated fully by a large 

 number of botanists and agriculturists, 

 live in what is technically called sym- 

 biotic relationship— i.e., both host plant 

 and bacterium being of mutual service 

 to each other. In a report of this 

 character it is unnecessary to more fully 

 explain this point, but it will suffice to 

 say that the bacteria which form charac- 

 teristic nodules on the roots of. the host 



plant, take nitrogen from the air, and 

 this nitrogen is afterwards available 

 in the soil as plant-food. The amount 

 of nitrogen thus added to the soil 

 varies with the species of the bacteria 

 and their numbers, but in the case of 

 one of the plants hereafter mentioned 

 experiments have shown it to be as 

 much as 200 lbs. per acre per year. 



Leguminous plants which possess these 

 bacteria may therefore be considered 

 as friends and not as foes, as useful 

 plants and not as weeds in a rubber 

 plantation. 



In order to get the maximum of benefit 

 from these plants it is necessary to cut 

 them down periodically and leave them 

 lying on the ground. The length of time 

 they should be allowed to grow depends 

 on the vigour of the plant, in most cases 

 about nine months. 



This cutting down need not be an ex- 

 pensive operation, as it is not intended 

 to eradicate the plant, but only to allow 

 the green parts to form a mulch on the 

 surface of the land and thus return 

 something to the soil. 



The operations of weeding must, as the 

 planter knows to his cost, be carried on 

 periodically and not be delayed, or the 

 weeds will get out of hand, and the cost 

 of eradication be very greatly increased 

 or made well nigh impossible, but the 

 cutting or hacking down the leguminous 

 green manure plants may be postponed 

 without danger until such time as labour 

 is available for the purpose. 



The three plants which seem to me 

 most suitable in Malaya for the purpose 

 above mentioned are: Crotalaria striata, 

 Mimosa <pudica and Desmodium triflo- 

 rum. 



Crotalaria striata is a quick-growing 

 vetch-like plant with trifoliate darkish 

 green leaves. In good soil with sufficient 

 rainfall it grows to a height of 6 feet in 

 about a year. When sown sufficiently 

 thick it completely covers the ground 

 within a few weeks, so that the clearing 

 is like a good lucerne or vetch crop in 

 Europe, and the surface of the ground is 

 not seen at all. 



It has been proved by experiments 

 with this plant in Ceylon that 14,000 lbs. 

 of organic matter were formed by crota- 

 laria under cacao, and the nitrogen in 

 this organic matter was equal to that in 

 1,7000 lbs. of castor cake or 700 lbs. of 

 nitrate of soda. Other plants — weeds 

 —cannot get enough light under the 

 dense cover of the crotalaria, and new 

 weeds are kept out as their seeds cannot 

 reach the ground which is so well 

 covered. If the crotalaria is sown in 

 good growing weather, and if the land is 

 clear of all weeds, no further weeding 



