8 SOIL FERTILITY. 



" Except in the case of very open soils in which organic 

 matter is so rapidly oxidised that very little humus is ever 

 found, there is a general tendency for the soils in this 

 country to l)ecome " sour " unless the acid substances, 

 formed by the decay of organic matter, are neutralised by 

 lime. If the soil does not naturally contain enough 

 calcium carbonate to effect this, frequent liming becomes a 

 paramount necessity." 



In a paper entitled " Lime Requirements of Certain 

 Soils," by H. B. Hutchinson and K. MacLennan*, a method 



N 



is given for the determination, bv means of -r- calcium 



■ oU 



bicarbonate solution, of the lime requirements of soil, 



and the following extract from this paper is given, as it 



bears upon the litmus paper test : 



'■ The simple and commonly adopted test for soil 

 acidity is that with litmus paper, in which a strip of neutral 

 paper is interposed for upwards of 15 minutes between 

 two masses of the moist soil to be tested. For rough work 

 in the field the method possesses a certain amount of value — 

 the production of a red tint generally being an indication 

 of acid soil conditions. On the other hand, however, the 

 failure to give any colour change does not necessarily 

 mean that the soil would not respond to an application of 

 lime. The Craibstone soil largely used in our experiments 

 failed to react to this test, but responded distinctly to treat- 

 ment with carbonate both in laboratory and pot culture 

 experiments. A refinement of the method has been intro- 

 duced by Christensen and Larsen, who used neutral litmus 

 solution and classified the soil according to the tint produced 

 in the test, etc., etc. 



" Of the soils tested by these investigators, 26 were 

 found to be acid or weakly acid in reaction and of these 

 only one failed to respond to treatment in the field ; of 

 50 soils found to give a neutral reaction, 58 per cent, still 

 responded to treatment and 14 per cent, were doubtful, 

 thus supporting the view expressed above with regard to 

 this test." 



♦Journal of Agricultural Science, Vol. vii , Part I. 1915. 



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