H. 13. HuTCHiNsox AND K. MacLennan 



99 



These results possess several points of interest. In the first place 

 the returns in plant growth are almost directly proportional to the 

 lighter dressings of carbonate supplied. Little difference is evident 

 between the yields resulting from the application of the lower equivalent 

 doses of oxide and carbonate until the requirements of the soil are 

 satisfied, i.e. the neutral point' — the slightly lower value with 0-10 per 

 cent, of oxide being due to an exceptional variation in the duplicates, 

 the other value being 8-20 grms. as against 8-27 grnis. with carbonate. 



Cui've 4. 



•09 -18 -SR Ti >.fm l-i^ 



per cent. Lime applied (in terms of C'aCUj) 



Tlie Ftolative Eifect of Calcium Oxide and Carbonate on Plant Growth 

 in an acid Soil (Wohurn), Crop, Barley. 



Secondly, the specific action of the oxide only becomes evident with 

 0-6 per cent, while the next higher dressing with this compound produces 

 a relative depression. These two high dressings were, in fact, made 

 on the results of the titration method described in the first part of 



^ This is of considerable practical importance; the view is often expressed, and great 

 stress has been laid upon it in the United States, that carbonate of lime (chiefly gromid 

 limestone) is the only form of lime that can be safely used in practice, on account of the 

 tendency of caustic lime to " bum up " the soil. The results obtained by us in labora- 

 tory and pot culture experiments appear to denote that until the reaction of the soil is 

 fully corrected, various decomposition changes proceed with similar rapidity with either 

 form of lime. It is only when excess quantities of oxide are employed — and this appears 

 to have been the case in several American and English experiments — that a sudden 

 liberation of soluble nitrogen compounds occurs in the soil, and local circumstances then 

 determine whether this plant food is assimilated by the first crop or is subject to leaching 

 during the following rainy season. If the latter takes place a heavily limed plot is liable 

 to become impoverished to a greater extent than less heavily or even unUmed soils, and 

 by decreased fertility in subsequent years tends to give support to the prevalent view of 

 the "burning" action of the caustic form. 



7—2 



