218 POWER OF THE SOIL TO ABSORB SALTS [chap. 



soil will be considered later (p. 253). Dyer has examined 

 the soils of the Rothamsted wheat plots which had then 

 been continuously manured in the same way for fifty 

 years, with the view of tracing the fate of the mineral 

 manures applied. The following table shows a com- 

 parison of the amounts of potash soluble in strong hydro- 

 chloric acid, in lbs. per acre, found in the top 9 inches 

 of soil from four of the plots; one (No. 11) received 

 nitrogen and phosphates, but no potash, every year, the 

 others were variously manured, but all received 200 lbs. 

 per acre of sulphate of potash. Estimates are also given 

 of the total amount of potash applied as manure and 

 removed in the crops over the whole period, so that in 

 the last two columns a comparison can be made between 

 the actual surplus of potash in the manured over the 

 unmanured soils, and the surplus calculated from the 

 differences between the potash added in the manure 

 and removed in the crops : — 



On the whole, about one-half of the estimated surplus 

 of potash received by the manured plots still remains in 

 the top 9 inches of soil. 



Dyer further estimated the proportions of potash in 

 the same soils which was soluble in a I per cent, solu- 



