20 



THE RUBBER TREE BOOK 



This is the first, and in some very acid soils the final stage. 

 Ammonia can serve as plant food. 



2. Those bacteria which, in their turn, by oxidation produce 

 nitrites from the ammonium compounds mentioned above. 



3. Those bacteria which act on the nitrites, and, by means 

 of oxidation, form nitrates. 



4. Those bacteria which procure nitrogen directly from 



FIG. 3. Photograph of Fine Garden Soil (magnified 36 times). 



the atmosphere, and of these there are two kinds: (a) Those 

 living free in the soil, and (b) those living in nodules upon the 

 roots of pod-bearing leguminous plants (as peas, beans, etc.). 



The fertility of soils is to be measured by the numbers 

 present and by the activity of these beneficial bacteria. It is 

 essential that these beneficial bacteria have a sufficient supply 

 of air in order that they may discharge their functions. In 

 water-logged, sour or dank soil they cannot act. Consequently, 

 by cultivating soil it is aerated, and, being aerated, its fertility 

 is marvellously increased. It is very important that rubber- 

 growers with flat, low-lying land and heavy soils should take 



