Oct. 14, 1918 Fertilizer Potash Residues in Hagerstown Silty Loam 79 



demonstrated that only after years of normal crops have been removed 

 is there any evidence of crop benefit by reason of potash applications. 



The amounts of soluble potash in the soil that was dressed with po- 

 tassic fertilizer are, no matter how weak the solvent used, relatively 

 much greater than are found in the untreated soil. This fact, together 

 with the composition of the crops grown on the respective lands, war- 

 rants the conclusion that the potash dressings remain, at least in part, 

 readily available for some years after the application. The excess 

 soluble in water corresponds to 1.4 times the annual addition; in carbo- 

 nated water, 2.6 times; in weak solution of a neutral salt, 5.2 times; 

 and in weak, warm acid, 6.3 times. 



It is a curious coincidence that the excess of potash dissolved by hot, 

 strong acid from the soil dressed with potash lacks very little of being 

 equal to the amount of this element added, 1881-1916, less the excess 

 quantity removed from plot 4 in the crops harvested (1,800-430= 1,370 

 pounds). That this closeness of agreement is merely a coincidence must 

 be evident from what has already been remarked concerning the large 

 efifects upon the strong acid extraction of soil potash that are observed 

 when the time or temperature conditions are slightly changed. Frear 

 and White {4, p. 187) have reported, from analyses of the sod lands ad- 

 jacent to and intersecting the tiers of plots under the general series of 

 experiments, that while the Association method of acid treatment re- 

 moves somewhat over 8 per cent of the potash of these sod-land surface 

 layers, Hilgard's method, which requires a 5-day instead of a lo-hour 

 treatment, increases to 22.7 per cent the proportions of the total potash 

 removed. 



Finally, it should be noted that, although the crops harvested from 

 plot 4 removed only two-ninths of the fertiHzer potash applied, only 

 three-eighteenths of the quantity applied remains in such condition that 

 it can be readily dissolved by warm, weak acid. These quantities leave 

 eleven-eighteenths of the applied amounts to be otherwise accounted for. 

 The figures for potash soluble in strong acid do not indicate that much 

 of this potash, except what the harvested crops took away, has been re- 

 moved from the surface soil. Most of it remains there in rather diffi- 

 cultly soluble condition. In other words, the residual potash tends to 

 assume, in large part, a condition of relatively slow availability. Con- 

 cerning the time relations of this change, little is known. Gilbert (5) 

 remarked a similar change in the solubility of the residues of fertilizer 

 potash in the loam soil at Rothamsted. 



SUMMARY 



A-companson, as to the condition of the potash in a Hagerstown silty 

 loam soil which has in the past 36 years received, in 18 equal biennial 

 dressings, 1,800 pounds of fertilizer potash, with that in a neighboring 



