7<) fjime Rer/uircments of Certain Soils 



It is necessary therefore in any particular case to decide firstly on 

 the type of change to be induced (sterilisation or neutralisation), and 

 secondly, the amount of lime required to bring about the desired effect. 

 The first consideration can only be decided by reference to the particular 

 conditions of each case, while guidance as to the second is afforded by 

 the two methods suggested below for the two distinct purposes. We 

 propose accordingly to divide the paper into two sections, viz.. 



Part I. The Determination of the Amount of Lime (CaO) necessary 

 to induce Partial Sterilisation Changes. 



Part II. The Determination of the Amount of Lime (CaO) or Chalk 

 (CaCOj) required for Soil NeutraUsation^. 



Part I. Lime Reqotrements for Partial Steriusation Purposes. 



The capacity of caustic lime to induce typical partial sterilisation 

 changes has been studied with a number of soils and the results of 

 these bacteriological, chemical and pot-culture observations have 

 already been given in detail elsewhere (5). The results thus obtained 

 serve as a check on those given by the method below. 



The addition to the soil of any partial sterilisation agent results 

 in changes of which the three chief are (a) an initial reduction in the 

 numbers of putrefactive bacteria, with a subsequent increase in numbers 

 and activity ; (b) the partial or complete inhibition of nitrifying organ- 

 isms, thus leading to accumulation of the ammonia produced by 

 break-down processes, and (c) a similar inhibition of the larger soil 

 protozoa. With the two latter, somewhat related effects on "soil 

 pests" might possibly be associated. 



During this work it was evident that the various soils differed 

 greatly in response to treatment and that the conventional methods 

 failed to give any index to this relative responsiveness. Since the 

 desired changes, chiefly of a biological nature, could only be due to an 

 alteration in the reaction of the soil solution, it was obviously necessary 

 to obtain some gauge of the absorptive power of the soil for lime. 



'■ This term is used with due reservation. Although the view has been advanced by 

 van Bemmelen (1) and Baumann and Gully (2) that the phenomena of "soil acidity" 

 may be explained on a purely physical basis, this has been severely criticised bj' Rindell (3) 

 and Tacke and Siichting (4) and the authors consider that it would be somewhat premature 

 to abandon the term "acidity." It is therefore used in these pages as convenient to 

 indicate "apparent acidity," "lack of basicity," or in this case "lime requirement"; 

 "neutralisation" may be interpreted as the correction of this condition. 



