418 MICROBIOLOGY OF SOIL 



as silicates, carbonates, phosphates, humates, sulphates, etc. In 

 humid climates the carbonates are being continually removed from 

 weathered rock material, as is plainly shown by the composition of 

 drainage waters. The losses become much greater in cultivated soils- 

 thanks to the humus and the microorganisms present in them. The 

 absolute amounts lost from year to year will depend on the proportion 

 of lime and magnesia in the soil, the mechanical composition of the 

 latter, its content of humus and the methods of tillage and fertilization. 

 According to Hall the soils of the experiment fields at Rothamsted, 

 containing about 3 per cent of calcium carbonate, are losing lime at the 

 rate of 362 kg. to 453 kg. (800 to 1,000 pounds) per acre 'annually. In 

 certain sections of Scotland where liming has been practised for a long 

 time the farmers estimate the loss of lime from the land at 6 bushels 

 per acre, annually; that is, approximately at the rate of 226 kg. to 

 272 kg. (500 to 600 pounds). In New Jersey, New York, Pennsylvania 

 and other eastern states farmers who use lime more or less regularly 

 apply i ton of it at the beginning of each five-year rotation. This would 

 provide for an annual loss of 181 kg. (400 pounds) per acre. The loss of 

 lime and magnesia is increased under intensive methods of agriculture. 

 When animal manures and green manures are employed, microbial 

 activities are stimulated, the production of carbon dioxide is encouraged 

 and the loss of the soluble calcium bicarbonate made greater. The 

 removal of lime is hastened even to a more striking extent when 

 ammonium salts are applied to the land. The resulting nitrification 

 and loss of lime are illustrated by the following equation: 



(NH 4 ) 2 SO 4 +,2CaCO 3 + 4 O 2 = Ca(NO 3 ) 2 + CaSO 4 + 4H 2 O+ 2 CO 2 



As was already indicated, the loss of calcium and magnesium car- 

 bonate from the soil is effected largely through the activities of bacteria 

 and of other microorganisms. At the same time microorganic life is 

 responsible for the restoration of varying amounts of carbonates. It 

 has been demonstrated that, in the weathering of the complex silicates, 

 carbonates and silicic acid may be formed in considerable quantities. 

 In the presence of decaying organic matter and the consequent evolu- 

 tion of carbon dioxide the formation of carbonates from silicates may 

 be extensive enough to balance the losses. Similarly, calcium carbonate 

 may be formed in the soil from humates and from the calcium salts of 

 simpler organic acids. They may be formed, also, through the activi- 



