D 
As fai as oxygen is concerned this element is of importance nut 
only in the atmosphere, but also in the soil. Here it plays an 
important part in the formation and transformation of most nutritive 
compounds, and it is essential in the ground, because the roots of 
plants breathe in the same way as the stems and branches breathe. 
Oxygen is also required by many bacteria, which are important for 
transforming certain foodstuffs into absorbable compounds, for 
instance, transforming ammonia into nitric acid, in which form the 
plants take most of their supply of nitrogen, and also for transform- 
ing decaying matter into absorbable substances. 
In a hard and compact soil the bacteria referred to do not thrive, 
and their well-being is only ensured by cultivation. 
If the ground is not properly ventilated suitable solutions cannot 
be formed either for want of water or for want of air, and it is thus 
obvious that a well aerated and permeable soil is of the greatest 
importance to the plants. 
On uncultivated land the water, which is the main factor in all 
plant life, cannot penetrate properly. After heavy showers it just 
runs off. and 1 believe that starvation of rubber trees is frequently 
due to an insufficient supply of water. 
Cultivation helps to retain the water, and between old trees it 
also helps to retain fallen leaves, which are often washed away if 
the surface is too smooth. 
Cultivation is- mostly done by changkolling and amongst old 
trees this cannot very well he done otherwise, but young clearings 
can almost always be treated cheaper and better by the use of 
agricultural implements, ploughs and harrows. 
In the course of time several different kinds of harrows have 
been tried on plantations, and at a certain period disc harrows 
were much in favour. On the estate with which I am connected 
we also tried some, but we did not find them satisfactory. In hard 
soil the discs could not work, and where they worked they only 
loosened a couple of inches of the soil, resulting in very bad wash. 
About two and a half years ago we commenced ploughing, and 
on one of our sections 2,200 acres out of 2,800 have been treated. 
The first ploughing was done by a small one- handled American 
plough, { * Luzon.” which did very good work, but since then a 
bigger type of a two-handled Danish plough, “ Fraugde,” has 
been introduced and is now used exclusively. It is quite au ordinary 
plough, but so strongly made, that it does not break when 
encountering the usual obstacles in the ground. 
1 know that some planters have tried ploughing and given 
it up on account of the difficulty of teaching the bullocks to drag the 
plough, but I may say that we have never experienced any trouble 
7 
