Wild. — Lime Reqiiivemenfs of certain Soils. 

 Table E. 



517 



* Second treatment of sample. 



t Result given in Table C, and repeated here for comparison. 



+ Means a positive requirement. 



— Means that the solution has taken up lime from the soil. 



These results indicate that all soils remove a certain quantity of lime 

 from the bicarbonate solution independently of their actual lime require- 

 ments, provided that the solution is above a certain concentration initially. 

 The Weka Pass soil can scarcely be in a different chemical condition as 

 regards lime to that from Waikari, since both contain a large excess of 

 calcium carbonate; and yet whereas the Waikari soil removed lime fi-om 

 solution, that from Weka Pass gave it up to its solution, the strength of 

 which was increased from 0-019 N to 0-02 N. 



No attempt is made in this paper to explain this phenomenon, nor will 

 any attempt be made to give a definition in chemical language of the term 

 " lime requirement." The aim of the work herein described is to find 

 whether the method gives results for a given soil which agree with what is 

 known from other sources of the lime requirements of that soil. Finding 

 this to be sufficiently near the case for practical purposes, the writer is for 

 the present prepared to accept the statement of Hutchinson that the amount 

 so indicated is actually the optimum for plant-growth. It has been shown, 

 however, that the result for any given soil varies with the strength of the 

 solution, and that in practice it is necessary to make the determination 

 under standard conditions. Either a solution of uniform strength must be 

 employed for all determinations, or a correcting factor must be applied. 

 As sufficient data has not yet been obtained to enable one to select a reliable 

 correcting factor, the use of a solution of standard concentration is recom- 

 mended, for by this means strictly comparable results are obtainable. 



It may be added that this work has brought out many points of more 

 theoretical interest, which will be discussed in another communication. 



