PHOSPHORUS 173 



of Scotland, where liming has been practised for some time, the loss 

 is from 500 to 600 pounds. In this country, where liming is necessary, 

 the farmers usually provide for a loss of 400 pounds an acre annually. 

 Bacteria are also responsible for the restoration of varying 

 amounts of carbonates.' In the weathering of complex silicates, 

 carbonates and silicic acid may be formed in considerable quantities : 



CaAl 2 Si 2 O 8 + CO 2 + 2H 2 O = Al 2 Si 2 O 5 (OH) 4 + CaCOs 



According to Nadson, soil bacteria may cause the formation of 

 calcium carbonate from calcium sulphate through the reacting of 

 ammonium carbonate formed in the decay of protein substances 

 with calcium sulphate: 



(NH 4 ) 2 CO 3 + CaSO 4 = (NH 4 ) 2 SO 4 + CaCO 3 



Or even after the sulphate has lost its oxygen through the action of 

 reducing bacteria, calcium carbonate may be formed through the 

 action of carbon dioxid and water on the calcium sulphid : 



CaS + CO 2 + H 2 O = CaCO 3 +. H 2 S 



Denitrifying bacteria may act on calcium nitrate with the forma- 

 tion of calcium carbonate: 



2Ca(NO 3 ) 2 + 2CO 2 - 2CaCO 3 + 2N 2 + 5O 2 



Calcium carbonate may also be formed in the soil due to the 

 action of bacteria upon humates and calcium salts of simpler organic 

 acids : 



(RCOO) 2 Ca = CaCOs + RCOR 



Cunningham has demonstrated that Azotobacter chroococcum is 

 capable of growing in solution of calcium oxalate with the formation 

 of calcium carbonate, as were also six other types of organisms 

 isolated by him. The presence of oxygen is essential for the process. 

 He considers that an equilibrium is set up by which the withdrawal 

 of calcium carbonate is balanced by the results of another set of 

 reactions which restores the base to the soil. This enables many 

 soils which contain only very small quantities of lime to retain their 

 neutral reaction and so to produce fair crops. This, however, is not 

 always the case, as is witnessed by the acid soils occurring in many 

 agricultural districts. 



Phosphorus. Phosphorus occurs mainly in the form of the calcium, 

 iron, or aluminum phosphate; in any soil the quantity soluble is 

 small. Moreover, as soluble phosphorus compounds are applied to 

 the soil they become fixed as insoluble compounds. Hence, the loss 

 through leaching of this element from the soil is small under any 

 conditions. 



