40 



size. Have a box made of these inside measurements and invert it 

 over the block of soil,and then remove the whole, box, soil, and all, 

 by putting a spade underneath the block, Then fasten a cover on the 

 box and send to the analyst, marking the end of the box which contains 

 what was originally the surface soil. The analyst has thus a block 

 showing the layers of soil as they occurred in situ down to 15 inches 

 deep, and valuable results may often be drawn from mere observation 

 of them, which would be entirely missed if merely a shovelful of soil 

 down to the same depth were sent for examination. 



IMPORTANCE OF VARIOUS SOIL CONSTITUENTS 

 Although the constituents always present in soil are many in 

 number, yet those which have any interest from an agricultural point 

 of view are comparatively few. Some seem to have no necessary 

 functions in regard to plant life. Such are the Silica, the Alumina 

 and the Soda. Others are, one may say, always present in far 

 greater amount than the plant requires. Such are the Oxide of 

 Iron, the Magnesia, and the Sulphuric Acid, but with these con- 

 stituents it may be that they have to be present in some particular 

 form to be useful to the plant, and thus they may be an essential 

 element in the fertility of a soil. And third there are those ingredi- 

 ents required by every plant, and upon whose absolute and relative 

 quantity depends primarily the fertility of the land. Such are 

 the Organic Matter, the Lime, the Phosphoric Acid, the Potash, 

 and the Nitrogen. We will in the first place consider the Organic 

 Matter and Nitrogen as they are related to the growth of the tea 

 plant in Assam. 



ORGANIC MATTER AND NITROGEN. 



These two constituents of the soil are intimately connected. In 

 fact the total useful nitrogen in the soil is or has been contained in 

 the organic matter. 1 say "has been" because at the time the tea 

 plant utilises it, it usually has been converted into nitrates by the 

 microbes of the soil. For many years it has been supposed that this 

 conversion into nitrates always took place before absorption of 

 nitrogen by the plant, and it is only recent investigations which 

 seem to have shown that the nitrogen in the organic matter itself 

 without previous change, may form the food of plants. The deter- 

 mination of the nitrates actually present in soil generally, however, 

 gives little information as to the resources of the soil in food supply 

 since the nitrogen in this form is in so soluble a condition, that the 



