1906.] How LONG DOES LiME LAST IN THE SOIL? 325 



larities in distribution of material like chalk, spread roughly by 

 hand, renders great exactitude in the conclusions impossible, but 

 the results from the various fields are in substantial agreement. 

 Calculated over various periods of from 38 to 32 years, we 

 obtain the following rate of loss of carbonate of lime per acre 

 per annum on the unmanured land : — Broadbalk Field (con- 

 tinuous wheat), 800 lb,; Hoos (continuous barley), i,coo lb. ; 

 Agdell (rotation), 930 lb. ; Little Hoos (mixed farming), i ,050 lb. 

 —figures which might at the outside require reducing by 20 per 

 cent, to allow for a possible consolidation of the soil during the 

 long period for which it has been cropped continuously without 

 manure. Speaking generally, we may conclude that by natural 

 causes alone the rain water will remove from an arable soil con- 

 taining originally more than i per cent, of carbonate of lime 

 about eight hundred to a thousand pounds per acre per annum, 

 which is equivalent to about half as much freshly burnt or quick 

 lime. When the amount of carbonate of lime in the soil is much 

 less than i per cent, the rate of loss will be considerably reduced, 

 though no data exist from which the diminution could be 

 estimated. These losses are almost wholly due to the solubility 

 of carbonate of lime in water containing carbonic acid ; the 

 pure rain water as it falls cannot dissolve carbonate of lime, but 

 after picking up some of the carbonic acid, which is always 

 present in the soil gases in large quantities, it becomes capable 

 of dissolving out the carbonate of lime. 



It should be noted that these results refer to arable land 

 receiving no manure, and carr3nng in consequence only a small 

 crop every year; whether the loss of carbonate of lime would be 

 reduced with the smaller percolation through the soil, which would 

 follow where larger crops were grown, or if the land were in grass, 

 cannot be settled from the data in our possession. " Lime sinks 

 in the soil" is a common farming maxim, but this conclusion is 

 based upon frequent observations of a layer of chalk or lime a few 

 inches, or even a foot or so, below the surface of old grass land. 

 Such sinking of lime, &c., in grass land is, however, brought about 

 by quite distinct causes, chiefly by the bur^'ing action of earth- 

 worms, which are always bringing the fine soil up to the surface. 

 The action of earthworms has been investigated by Darwin, 

 who found that the rate at which they bring the mould to the 



