1905.] 



On the Retention of Bases by the Soil. 



21 



induced by the use of ammonium salts is less than half that required for the 

 absorption and subsequent nitrification of the ammonia; (2) where sodium 

 nitrate or (3) where farmyard manure is applied, the rate of loss of calcium 

 carbonate is below that of unniatmred land. 



Further evidence that there must be under normal conditions some action 

 at work protecting or renewing the bases of the soil may be gathered from 

 the continued fertility of many soils containing but a trace of calcium 

 carbonate. The following analyses may be quoted of soils that have fallen 

 under the personal observation of one of us, soils which, despite their very 

 low content of calcium carbonate, have continued to give crops under arable 

 cultivation for a long period. 



Table XL — Calcium Carbonate per cent, in various Soils. 



Formation. 



London 

 clay. 



London 

 clay. 



aault 

 clay. 



Weald 

 clay. 



Bagshot 

 sand. 



Thanet 

 beds. 



Woburn Experimental Farm, 

 Stackyard Field. Barley. 



Locality. 



Wanboro', 

 Surrey. 



Ashtead 

 Common. 



Alder 

 Holt. 



Staple- 

 hurst, 

 Kent. 



Bisley, 



Woodnes- 

 borough. 



1876. 



1903. 

 Plot 2a. 



1903. 

 Plot 3. 



1903. 

 Rotation. 



1st depth ... 

 2nd depth ... 



p. c. 

 0-065 

 0-084 



p. c. 

 0-002 

 nil 



p. c. 

 0-04 

 0-16 



p. c. 

 0-037 

 0-012 



p. c. 

 0-008 

 0-016 



p. c. 

 0-018 

 0-010 



p. c. 

 0-087 

 0-066 



p. c. 

 051 

 0-044 



p. c. 

 0-070 

 0-042 



p. c. 

 0-089 

 0-071 



Another striking case is afforded by the Stackyard Field on the farm of the 

 Royal Agricultural Society at Woburn, which has been under experiment 

 since 1876. Table XI also shows a series of determinations of calcium 

 carbonate in the soil of this field taken at the beginning of the experiments 

 and in 1902. The amount of calcium carbonate present is exceedingly small, 

 barely determinable in fact, yet the plots continue to yield normal crops, 

 except those which have been manured with ammonium salts. The latter 

 in recent years have become almost sterile, showing an acid reaction to litmus 

 paper and refusing to grow wheat or barley unless they first receive a dressing 

 of lime* 



Now in all these cases, however low the proportion of calcium carbonate 

 may be, the action of the percolating water must remove some of it, and the 

 recurring process of nitrification also demands a base. Yet the small quantity 

 of base available does not disappear entirely so as to render the soil unfertile, 

 unless some specially calcium carbonate consuming material, like the 

 ammonium salts, is employed as a manure. The continued fertility of such 



* See J. A. Voeleker, ' Journ. Roy. Agri. Soc., 5 3rd Series, vol. 10, 1899, p. 585, and 

 vol. 62, 1901, p. 272. 



