vi.] INTERPRETATION OF RESULTS 171 



like the slime fungus which causes " finger-and-toe " 

 in turnips, etc., are only prevalent when the soil is 

 losing its neutral condition, and are not found when a 

 sufficiency of calcium carbonate is present. The normal 

 changes in a soil are brought about by bacteria, which 

 only flourish when the medium is neutral or very faintly 

 alkaline ; as soon as the soil becomes acid the bacterial 

 actions are largely suspended, and in their place 

 moulds and other micro-fungi become predominant. 

 For reasons already stated (p. 50), it is impossible to 

 determine whether a soil is really acid or not by its 

 reaction to litmus paper. When, however, the filtered 

 extract from a soil turns blue litmus red the soil may 

 be regarded as acid. Many soils, however, which fail 

 to give a certain acid indication are in need of lime, and 

 Hutchinson and MacLennan have devised a method for 

 determining these lime requirements which appears to 

 agree very well with the behaviour of the soils in the field 

 {Jour. Agric. Sci., 7, 191 5, 75). The soil is shaken with 

 a solution . of calcium bicarbonate of approximately 

 N/50 strength for three hours and the amount of 

 calcium carbonate absorbed is measured by titration. 

 The amount of lime thus absorbed, calculated with 

 respect to the weight of soil used, gives the optimum 

 dressing of lime which should be applied to the land 

 and will there bring about neutrality. An excess of 

 caustic lime may cause harm, inducing certain effects 

 of partial sterilisation and a too rapid exhaustion of 

 the reserves in the soil to the detriment of succeeding 

 crops, but this action does not take place if an excess 

 of lime in the form of carbonate is supplied. 



Interpretation of the Results of a Soil Analysis. 



Though much may doubtless be learnt by a com- 

 parison of the analysis of a given soil with the analysis 



