470 Transactions. 



return would be required for a further application to prove profitable 

 Another point is that the effect of lime is seen rather in the pastures than 

 in the cereal or root crops. At Edendale they say that a want of some- 

 thing in the soil was seen not so much by low yields of oats or turnips as 

 in the ill health and lack of condition of stock depastured in these fields. 



Taking into consideration these facts, as well as observations of the 

 absorption of average Canterbury Plains soils, we have come to the con- 

 clusion that, while lime is no doubt urgently needed where the absorption 

 is greater than about 0-20 per cent., there is no proof from the point of 

 view of crop-production that it is required where the absorption is less 

 than about 0-10 per cent. To translate the indication of the Hutchinson- 

 MacLennan method into practical terms, therefore, we suggest the use of 

 this figure as a correcting value to be deducted from the actual indication 

 in order to get the probable practical requirement. The quantity 0-10 per 

 cent, is selected as being the present lime requirement indicated for field 21 

 of the Lincoln College Farm, which received 6 cwt. of lime in the winter 

 of 1915, and which is now in an entirely satisfactory productive condition. 

 A higher value — say, 0-14 per cent. — may perhaps be allowed for Southland 

 soils. 



Our conclusions, however, must be taken strictly in the sense in which 

 they are here recorded. We do not attempt to insist that liming the soils 

 of the Canterbury Plains will not pay ; but it is certainly the case that 

 while the benefits of liming have thrust themselves under the notice of 

 Southland farmers, they have not been sufficiently obvious to those farmers 

 in Canterbury who have made the experiment. Nor is it necessary for us 

 to say that we fully recognize that a manurial application may be more 

 than paying its way though the fact may not be obvious simply by viewing 

 the plots without measurements. Our conservative attitude is dictated by 

 the considerations — first, that there is as yet no positive experimental 

 evidence proving the economic importance of lime to these soils ; secondly, 

 that satisfactory results are being obtained without liming ; thirdly, that 

 whereas a kind of natural selection operating among methods of farming 

 the Southland Plains soils brought about the evolution of the practice of 

 liming, the same processes have not achieved similar results in Canterbury. 



Reason for greater acidity of Southland Plains soils : A search for 

 reasons for the greater lime requirements of Southland Plains soils on the 

 one hand, and those of the river-flats and of Canterbury Plains on the 

 other, led to the conclusion that the greater acidity and higher lime require- 

 ment of the soils of the Southland Plains appears to be due to a combina- 

 tion of lack of natural under-drainage (owing to more or less impervious 

 clay subsoil) and high rainfall, which together prevent aeration and oxida- 

 tion of organic matter, so that " sour" humus accumulates in the soil. The 

 reasons for this conclusion are set forth in the article in the Journal of 

 Agricultural Science already mentioned. 



Part II. — An Investigation of the Theory of the Method. 



The principal object of this investigation was to ascertain, if possible, 

 the nature of the action by which lime is taken up by the soil. At least 

 two explanations have been offered — 



(1.) The phenomenon is a mass-action effect, the calcium base com- 

 bining with the so-called humous acid of the soil. 

 (2.) The interaction between calcium salts and soil is due to " adsorp- 

 tion " by soil colloids. 



