134 Fertilisers [pt. in 



war, and the products are likely to be obtainable in 

 immense quantities in the future^ 



In its general action sulphate of ammonia differs but 

 little from nitrate of soda, and the choice between them 

 is mainh' one of price and convenience. It possesses, 

 however, certain characteristic features which some- 

 times assumes considerable importance. 



When applied to the soil it reacts with the calcium 

 carbonate, giving rise to calcium sulphate and am- 

 monium carbonate. The calcium sulphate washes out 

 in the drainage-water, but the ammonium carbonate 

 does not, bemg absorbed by some of the reactive con- 

 stituents of the soil (p, 21). The ammonium carbonate 

 becomes nitrified by bacterial action, and presumably 

 is changed to calcium nitrate through interaction with 

 more calcium carbonate. Thus the complete change re- 

 quires that one molecule of ammonium sulphate should 

 react with two molecules of calcium carbonate, thus : 



(NH4)2S04 4- 2CaC03 + 8O2 



- CaSO^ + Ca(N03)2 + 4H2O + 2CO2. 



On this basis a dressing of 132 lbs. of ammonium 

 sulphate {i.e., one molecular weight) involves the re- 

 moval from the soil of 200 lbs. of calcium carbonate. 

 Now actual analyses at Rothamsted show that only one 

 half of this quantity, i.e., only 100 lbs., is removed, 

 and further experiment has shown that the calcium 

 nitrate is not whoUy retained by the plant but the cal- 

 cium is left in the soil and re-converted into carbonate^. 



There still remains, however, a loss of 100 lbs. of cal- 

 cium carbonate for each 132 lbs. of ammonium sulphate 

 applied, and on soils deficient in lime this becomes very 



^ Hall and Miller, Proc. Roy. Soc, 1905, 77 b, I 32. 



