CHAPTER V 



PLANT FOOD IN THE SOIL 



WHILE plants get the larger part of their bulk 

 from carbonaceous material constructed from 

 carbon taken out of the air, we have seen that 

 the elements which they get dissolved in the soil water 

 through their roots are of vital importance, for without the 

 water itself the carbon would be useless, and without 

 the nitrogen there could be no protoplasm to continue the 

 life work of the plant. A fertile and productive soil 

 is not only one in which there is a good supply of the 

 elements which the plant gets from the soil, but one in 

 which the mechanical texture is such, and the condition 

 of the plant food is such, that the roots of plants can make 

 use of the food. 



Years ago the notion prevailed that all that was neces- 

 sary to show the farmer how to improve the productive- 

 ness of his soil was for the chemist to make an analysis of 

 it and show him what it lacked so that he could add the 

 lacking materials. But experience has shown that this 

 analysis is of Httle value to the farmer, for the chemist can 

 simply tell him what the soil contains, but cannot tell him 

 whether plants can use these materials or not. 



Sometimes certain plant foods, especially potash, which 

 are in an unavailable condition in the soil, may be made 

 available by the use of Hme or plaster, which is the sul- 

 phate of lime, and many farmers seeing that lime helps 



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