LIMESTONE 



From eight plots on Hoos Field, where barley is grown every 

 year, the following losses of calcium carbonate have occurred: 



TABLE 28. LOSSES OF CALCIUM CARBONATE FROM Hoos FIELD, ROTHAMSTED, 



FROM 1865 TO 1905 



The average of the eight plots on Hoos Field shows for 40 years 

 an average annual loss of 800 of calcium carbonate per acre. The 

 ammonium salts have not markedly increased the average loss on 

 this field above that from the nitrate plots or the untreated land. 



The investigations reported also include Agdell Field and Little 

 Hoos Field, both of which have lost calcium carbonate in about the 

 same amount as Broadbalk and Hoos. 



Practice based upon these results would require an application 

 of two tons per acre of ground limestone about every five or six 

 years, in order to replace the regular losses. 



The loss of calcium carbonate from soils is largely due to leach- 

 ing. The soil waters contain carbonic acid (H 2 CO 3 ) formed by the 

 absorption of carbon dioxid (CO 2 ) from the atmospheric air and 

 from the soil air. This carbonic acid has power to react with cal- 

 cium carbonate and form calcium bicarbonate, CaH 2 (CO 3 ) 2 , which 

 is soluble in water, thus: 



H Os 



Ca 





< >C= 

 ^(y 







H O\ /> 



>C=0 = Ca< 

 K0' ^O 



=0 



H- 



