Soluble Constitiienfst hi Alia rial Soil. 57 



ClieiJiical lUMiiures, especially solul>le phosphatic ones, should 

 not be applied in any quantity to soils poor in Imnius, except in 

 conipany with farmyard manure or some form of humus. 



The soil is a changeaible matrix, whose percenrap:e snluiiilitv 

 in water and acid varies appreciably at different depths tlir()U<j;h- 

 out the year, and also underp-oes >^easonal changes as a whole, 

 especially under the action of chemical manures. The apparent 

 losses from the soil after heavy manuring are many times 

 greater than the ash contained in the crop, and also gi-eater than 

 the amount added to the soil by any of the chemical manures 

 used excepting lime. 



The oxidation and nitrification of humus in the soil is more 

 favoured by air-slaked lime tlian by the direct application of 

 quicklime, so long ais the latter retains any alkalinity injurious 

 to nitrifying micro-organisms. 



Postscript. 



Since the above was written, Mr. Hall has drawn my atten- 

 tion to the fact that Norman Taylor, in Maclvor's " Chemistry 

 of Agi'iculture," 1879, p. 224, suggested that the superficial 

 limestone deposits common in the Mallee may have been pro- 

 duced by the continued drarwing up of chalk in solution by 

 Ciupillary action from the moister layers below. This ex- 

 planation was adopted by Howchin for the desert limestones 

 around Adelaide, and was extended by Gregory (" Geography 

 of Victoria," 1903, p. 93) to the hard siliceous superficial cherts 

 or quartzite beds, and also to the ironstones of superficial gold 

 deposit>'. Recent research has, however, show-u that iron bac- 

 teria may play a most important part in the formation of iron 

 deposits wherever water is present, and such deposits will, in 

 the first instance, be superficial. In any case, the data obtained 

 by me are insufficient to do more than establish the fact that 

 uuiterial may ri^e to the surface in dry weather, but say nothing 

 as to whether wet weather may not waish it down again to an 

 equally great extent. The alkaline ash left after bush fires 

 would certainly tend to carry silica downwards again as soon 

 an anv rain fell. 



