48 



a matter for experiment. In connection with this matter I have 

 recently been informed that a dressing of the soil with sulphur has 

 been found very beneficial on these village sites, in a few places. 

 This method is worth trial, but it is one the reason for which is 

 somewhat difficult to see. 



"LAW OF THE MINIMUM." 



But organic matter and nitrogen are not the only constituents 

 required in the soil for the production of healthy and luxuriant 

 bushes and of high quality tea. For both these results they occupy 

 essentially the most important position, but without other ingre- 

 dients they would be utterly useless. There is a law in agriculture 

 known as the " law of the minimum," which states that if the mini- 

 mum required by a plant of any constituent be not obtainable, 

 all others are there in vain and the plant cannot be grown. Inas- 

 much as the tea plant requires Phosphoric Acid, Potash, Oxide of 

 Iron, and Lime at least, and probably Magnesia as well, it is ab- 

 solutely necessary that these should be present in sufficient quantity 

 and in a sufficiently available form for the plant to grow well. I 

 say " in a sufficiently available form " because they may and often 

 are present, but in such a condition that the plant cannot use them. 

 Thus, for instance, the quantity of Potash in a clay soil is invariably 

 several times greater than in sandy land, and yet the latter may be 

 actually richer agriculturally in this constituent at any particular 

 moment than the former, simply because in the former case it is so 

 combined in the clay as to be in large measure useless for the plant : 

 again, Phosphoric Acid is always less useful in the presence of large 

 quantities of Oxide of Iron and Alumina than in their absence, &c. 

 We have a direct test for the actually available amount of these 

 constituents, and this I have used in special cases, as will be noticed. 



PHOSPHORIC ACID. 



Of the constituents I have named, the Phosphoric Acid is the 

 most important. Its presence in greater or less amounts depends 

 entirely upon the kind of rocks from which the soil is derived. It 

 happens that in the Himalayas, whence the greater part of the alluvial 

 soil of the Assam valley is derived, the rocks as a whole are poor in 

 phosphates, and hence likewise the soils in this valley are compara- 

 tively poor in this constituent. This is generally more marked, 

 though with some striking exceptions, as one descends the river. An 

 amount equal to '25 per cent, at least on the non-sandy part of the 



