H. B. Hutchinson and K. MacLennan 79 



radically the biological conditions obtaining therein. This we find to 

 be the case with all the soils over which an adequate control has been 

 exercised. For purposes of comparison the relations of the nitrifying 

 organisms and the larger soil protozoa towards treatment are given in 

 the following table. 



Table II. The Relation between the Critical Point iiidiaited bi^ 

 Titration Method and the AnwKnls of Lime necessari/ to induce 

 certain changes in various Soils. 



Botham- .,.,,, , ,,, , ,,, , Craib- 



„*„j Millliruuk: Woburn Chelsea , . 

 stect stone 



Critical point indicated by titration 



method 

 Inhibition of nitrification 



(laboratory experiment) 

 Destruction of larger protozoa 



(laboratory experiment) 

 Maximum growth of 1st crop 



(pot experiment) 

 Maximum growth of first four crops 



The titration method therefore allows of a good approximation of 

 the probable biological changes resulting from treatment of a soil with 

 a given quantity of caustic hnie. With respect to the crop producing 

 power of treated soils the conditions are somewhat more complicated. 

 Laboratory work has shown that the returns of nitrogen as ammonia 

 and nitrate are fairly proportional to the amount of lime applied (i.e. 

 within the first 9-12 months), but in heavily limed soils this nitrogen 

 is largely in the form of ammonia. Consequently, plants growing in 

 such soils obtain their nitrogen in a non-nitrate form and utilise it, as 

 has been frequently demonstrated, in an uneconomical manner; 

 hence no direct relation exists between the total ammonia and nitrate 

 produced in two differently limed soils — in the one case where the 

 nitrogen is chiefly in the form of nitrate, and in the other in the form of 

 ammonia. The pot experiments carried out with the above soils have 

 served to show, however, that an application to a soil of an amount of 

 caustic lime equal to that indicated by the titration method results 

 (a) in a maximum juoduction of dry matter in the first crop — heavier 

 appHcations tending to give a relative or actual depression, thus con- 

 stituting "over-liming," and (h) in a maximum growth of the four crops 

 used in our experiments. Hence the method proposed may serve as 



