Mineral Manure with and without Potash. 157 



reversed. There is an average produce of nearly one-fourth 

 less hay, and of over one-fourth less nitrogen and mineral 

 matter taken up, on plot 8 without than on plot 7 with potash, 

 so that the falling off in the produce on the exclusion of potash 

 was very great. The number of species remained about the 

 same on the two plots, but the percentage of Leguminosse has 

 greatly diminished since the exclusion of potash. Without 

 the potash the grasses became more leafy, less dense, and 

 showed much less tendency to mature. The great difference 

 in the amount of the total leguminous herbage on the two 

 plots is due to the marked increase of the surface-rooting 

 Lathyrus pratensis with the potash, and its greatly reduced 

 growth without it. Of the deep-rooting and hardy Lotus 

 comic ulat us there was the more without the potash. 



Excepting only silica and soda, less of every mineral con- 

 stituent potash, lime, magnesia, phosphoric acid, sulphuric 

 a^id was taken up on plot 8 without potash than on plot 7 

 with the potash. In the dry substance the percentage of 

 potash was less than two-thirds as high on plot 8 as on 

 plot 7, though it was still much higher than on the 

 unmanured plot, as also was the percentage of phosphoric 

 acid. 



The falling off in the total weight of produce, and in the 

 description and character of development of the herbage on 

 plot 8, must be attributed to the deficiency of available 

 potash. 



An interesting line of inquiry is suggested as to whether on 

 plot 8 the potash taken up by the herbage was derived from 

 the residue of the potash applied during the first six years, or 

 was furnished directly by the soil. That certain soils do, as 

 a matter of fact, retain a residue of supplied potash, and in a 

 slowly available condition, for very many years, is con- 

 clusively proved by evidence of very different kinds. Thus, 

 in the Rothamsted experiments, in which wheat has been 

 grown continuously for many years on the same land, the 

 effects of the residue of potash supplied more than twenty- 



