viii.] POTASH 253 



Thus the use of ammonium salts increases the 

 normal loss of calcium carbonate experienced by the 

 soil (due to solution as bicarbonate), and the amount 

 removed increases with the larger applications of 

 ammonium salts. Taking the mean of these and other 

 results obtained at Rothamsted, 200 lbs. of ammonium 

 salts causes a removal of about 120 lbs. calcium 

 carbonate, whereas the amount calculated from the 

 equation given above would be about 160 lbs. That 

 the loss from the plots receiving sodium nitrate and 

 dung is less than from the unmanured plot, is due, in 

 the former case, to the base left in the soil by the growth 

 of plants which derive their nitrogen from sodium nitrate, 

 and in the latter, to calcium carbonate formed by 

 bacterial action from organic calcium salts in the dung. 



The Absorption of Potash. 



In all respects the absorption of potash follows the 

 same laws as that of ammonia : i.e., caustic potash 

 is absorbed directly, but with sulphate, nitrate, and 

 chloride of potash the adsorption of the base is 

 accompanied by an attack of the acids set free upon 

 the calcium or other bases in the double silicates of 

 the soil, so that the solution is left neutral. In the 

 ordinary way potash is retained and calcium sulphate, 

 nitrate, or chloride, appear in the water draining 

 through the soil. Voelcker found in laboratory experi- 

 ments with small quantities of soil that potassium 

 carbonate was more freely absorbed than sulphate, 

 and that clays, marls, and pasture soils were more 

 effective in retaining potash than light loams or sands, 

 which latter had but little absorbing power. 



The following table shows some of the results 

 obtained when potash and soda salts were compared : 



