:h. i 



SOIL 13 



md that which is deep for one species may be shallow 

 [for another. As an example may be cited the Jhand 

 \(Prosopis spicigera) of the Panjab, which sends its 

 taproot sometimes to a depth of 27 metres (90 feet), 

 while, in digging a well in Oudh, roots of Sal (Shorea 

 \robusta) were found to have penetrated to a depth of 

 18 metres (60 feet). 



The above remarks will suffice to show how important 

 the physical properties of a soil are with respect to 

 plant life ; indeed, it is generally agreed that they are the 

 most important factors. American authors go so far as 

 to make soil fertility chiefly dependent on physical 

 properties and on the presence or absence of injurious 

 ingredients in the soil. 



Apart from the carbon which the plants derive 

 through their leaves direct from the atmosphere, they 

 obtain from the soil certain nutritive substances which 

 are compounds of calcium, potassium, sodium, nitrogen, 

 magnesium, phosphorus, iron, and a few others. This 

 food, as far as evidence is available, is taken up in a 

 solution made by the carbonic acid generated by micro- 

 organisms or by plant roots. 1 It has also been proved 

 that the addition to the soil in the way of the organic 

 manures, and also of nitrates, phosphates, potassium salts, 

 and calcium carbonate, increases the strength of a crop. 



The American theory is, then, that the soil is formed 

 by the disintegration and not by the decomposition of 

 rocks, and that all soils are able to yield the same 

 soil solution, containing all that is necessary to plant 

 food, and that what is taken up by the plant is replaced 

 in the solution from the soil. The chief difference 

 between the different soils is in the manner in which 

 the soil solution is yielded to the plants, this degree 

 being dependent on the texture or grain of the soil and 

 on the presence or absence of toxic substances. The 

 addition of manures has the effect of improving the 

 grain and in removing or oxidating the toxic substances. 

 It is also contended that if a soil be allowed to lie 



1 Dr. E. J. Russell, loc. cit. p. 136. 



