539 



plant, take nitrogen from the air, and this nitrogen is afterwards avai- 

 lable 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 expensive 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 legu- 

 minous 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 Dcsmodium triflorum. 



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 crotalaria under cacao, 

 and the nitrogen in this organic matter was equal to that in 1,700 lbs., 

 of castor cake or 700 lbs. of nitrate of soda. Other plants — weeds 

 — cannot get enough light under the dense cover of the crotolaria, 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 should be 

 necessary, but in the case of land which is thoroughly permeated with 

 the underground stems of lalang or with the roots of other weeds it 

 may be found that during the first two or three months weeding is 

 necessary. The crotalaria seed is sown broadcast. As to the quantity 

 to be used per acre it is better to sow more than is necessary than to 

 leave bare patches where weeds can thrive. Mr. Lauder Watson, who 

 is the first Federated Malay States planter to use this plant in rubber 

 planting, informs me that on Lauderdale, where the photograph of 

 crotalaria was taken, he used about 7 lbs. I have seen good results 

 from using only 4 lbs. per acre. 



Mimosa pudica, the "sensitive plant," which was another of the 

 plants suggested in the last annual report, is in many ways the pest of 



