84 Lime Requirement of Certn'ni Soih 



Danish " Inline Committee," Christensen and Larsen correlated the 

 results of the examination of a number of soils by this and other 

 methods with the results of field trials. Those obtained with the 

 ammonium chloride method are given below. 



The probable "lime requirement" limit is thus about 0-16-0-20 %, 

 but of the total number of cases there remain about 40 % in which 

 little guidance is given by the method. 



The Determination of Soil "Acidity." 



(o) Qualitative Methods. 



The simple and commonly adopted test for soil acidity is that with 

 litmus paper, in which a strip of neutral paper is interposed for upwards 

 of 15 minutes between two masses of the moist soil to be tested. For 

 rough work in the field the method possesses a certain amount of value — 

 the production of a red tint generally being an indication of acid soil 

 conditions. On the other hand, however, the failure to give any colour 

 change does not necessarily mean that the soil would not respond to 

 an application of lime. The Craibstone soil largely used in our experi- 

 ments failed to react to this test, but responded distinctly to treatment 

 with carbonate both in laboratory and pot culture experiments. A 

 refinement of the method has been introduced by Christensen and 

 Larsen (18), who used neutral litmus solution and classified the soils 

 according to the tint produced in the test. In the test, 1 c.c. of a neutral 

 litmus solution and 20 c.c. of distilled water are placed in test tubes of 

 about 40 c.c. capacity; -5 grms. of soil are then added, shaken up. and 

 allowed to stand until the following day. According to the tint produced, 

 the soils may be grouped into acid, weakly acid, neutral and alkaUne 

 types. Of the soils tested by these investigators, 26 were found to be 

 acid or weakly acid in reaction and of these only one failed to respond 

 to treatment in the field ; of 50 soils found to give a neutral reaction, 

 58 per cent, still responded to treatment and 14 per cent, were doubtful, 

 thus supporting the view expressed above with regard to this test. 



Loew (19) employed a method based on the liberation of iodine from 

 potassium iodide added to the soil and the production of a blue colour 

 with starch, while Daikuhara (20) suggests the following test: 5 grms. 

 of the soil are placed in a test tube and a 10 % solution of potassium 

 nitrite (chemically pure, and especially free from carbonate) is added 

 drop by drop until the soil is moderately moistened ; the mouth of the 



