328 How LONG DOES LiME LAST IN THE SOIL? [SEPT., 



where organic matter like farmyard manure decays, although 

 humic acids are produced which combine with carbonate of lime 

 in the soil, yet a still further stage of decay is brought about by 

 other bacteria, and the material is still further oxidized to car- 

 bonate of lime again. Plant residues also contain salts like calcium 

 oxalate which are resolved by soil bacteria into carbonate of 

 lime. Thus the investigations demonstrate that a number of 

 processes are normally going on in the soil which re-create the 

 carbonate of lime consumed by nitrification and similar pro- 

 cesses ; the only loss of carbonate of lime which is not com- 

 pensated for being its direct solution in rain-water containing 

 carbonic acid, followed by percolation into the drains or the 

 subsoil. When, however, the original stock of carbonate of lime 

 in the soil is very small this loss by solution becomes greatly 

 reduced and is negligible, so that the soil may retain a fairly 

 healthy condition under ordinary farming. 



It by no means follows, however, that a soil apparently 

 healthy and showing no sign of approaching sterility will not 

 be greatly benefi*:ed by a dressing of lime and chalk. The data 

 are insufficient yet: to enable us to fix the danger limit, but 

 probably it lies between one-half and one-quarter per cent, and 

 as soon as the carbonate of lime in the soil falls below that 

 limit the productiveness declines in various directions. 



Putting aside the manner in which lime neutralizes actual 

 acidity in the soil, with its resulting sterility, the beneficial 

 effects of lime are as follows : — 



(i) It improves the texture of the soil by coagulating the. 

 finest particles of the clay and rendering the land drier and 

 more friable. Drainage goes on more readily, the land is warmer, 

 and it is more readily worked to a good tilth. It is difficult to 

 exaggerate the value of this action of lime on the heavier soils ; 

 it often means that it is possible to secure a seed bed when the 

 unlimed land is still too wet to work, and the character of the 

 root crop, particularly swedes, depends more on securing a good 

 tilth than on manuring. A good example of the value of lime 

 in this connection may be gathered from the Rothamsted 

 experiments. In former years one of the fields, Geescroft, was 

 used for experiments upon beans and oats ; the land, hov/ever, 

 lay so wet, and was so difficult to work in the spring, that during 



