CHAPTER XIV 



SOIL AND FERTILIZER ANALYSIS 



The analysis of soils and fertilizers is such an important 

 part, both of scientific and practical agriculture, that there 

 is necessary a brief discussion of the terms used, of the possi- 

 bilities and limitations of such work, and of the immediate 

 value. 



209. How Analytical Results are Expressed. — It is custom- 

 ary in ordinary analytical work to express results in terms 

 of the oxide of the element, thus: CaO, K 2 0, Fe 2 3 , P2O5. 

 This is not the form in which these elements occur, but 

 is a convenient and conventional means of expression. In 

 fertilizer work the elements usually determined are nitrogen, 

 phosphorus, and potassium, and reported as nitrogen, N, 

 phosphoric acid, P 2 5 , and potash, K 2 0. Phosphoric acid 

 is not the correct name for the oxide of phosphorus — P 2 5 — 

 but since the oxide is the acid oxide there is some excuse for 

 it. Furthermore, it is not consistent to express nitrogen 

 as the element, and phosphorus and potassium as the oxides. 

 There is a desire on the part of some chemists to express 

 these and other results in the elemental form. It is the 

 logical way to do, but since custom is so strong, and since 

 most farmers and scientists think in the conventional terms, 

 these inconsistent forms have been used here. 



210. Soil Analysis. — The popular conception of the pur- 

 pose of soil analysis is to ascertain the fertilizer deficiencies 

 of a soil. That is, by determining in some way the amount 

 of nitrogen, phosphoric acid, and potash, the need of a 

 soil for any particular element can be predicted. This 

 idea has resulted, of course, in the development of a large 

 number of methods, and in the analyses of a large number 



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