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(hoeing) or disc ploughing is resorted to and bene- 
ficial results have been claimed, but no controlled 
experiments are reported in Malaya, while recent 
work in Sumatra extending over three years shows 
no positive results following cultivation in the case 
of rubber of seven years of age. It seems unlikely 
that cultivation of soil will ever become general, or 
that its adoption will be justified. 
Weeding. Clean weeding has long been generally 
adopted ; in addition to freeing the 
trees from competition, supervision and movement 
are rendered easier and the light, incidental cultiva- 
tion is of value by breaking up the hard surface 
cake or glaze which is readily formed on some soils, 
and through which rain penetrates with difficulty. 
On flat land there is much in favour of clean weed- 
ing, but on hilly land it is thoroughly bad and has 
resulted in considerable damage by soil wash. 
Realisation of this fact, together with the present 
need for economy, has directed increased attention 
to the use of cover crops. 
Cover Crops. The advantages of cover crops are: 
reduction of working costs, by obviat- 
ing weeding; and conservation of the soil. The 
disadvantages are the difficulties of eradication, 
supervision, movement, and in some cases of early 
identification of root diseases. Centrosema Plumieri 
is at present the most popular and useful cover for 
soil in good condition, but cannot be established on 
poor or badly washed soils. Giant Mimosa ( Mimosa 
Invisa) will grow on comparatively poor and badly 
washed soils. It is necessary to confine this cover 
to strips between the rows of trees on account of 
the formidable spines on its stem. On undulating 
