90 MASS. EXPERIMENT STATION BULLETIN 165. 



it has a slight solvent action on potassium in the absence of lime is shown 

 in the percolation experiment, where more is removed from the unlimed 

 plots than from the hmed. This may be more beneficial than harmful, as 

 it will make more potash available for the use of plants. 



(e) The use of ammonium sulfate probably does not cause the accumu- 

 lation of sulfates in the soil, as is indicated by the marked removal of sul- 

 fates from the sulfate plots in aU of the experiments. All of the soil 

 extracts were neutral to indicators, showing that no free soluble acids 

 were present in the soil. The absence of free acids is further shown bj'' 

 the amounts of calcium absorbed. Using different calcium solutions, no 

 difference in the amount of calcium absorbed is found between the 

 limed and unhmed ends. If a free acid or acids were present in the soil 

 from the unlimed areas, these soils should have absorbed a greater 

 amount of hme than the soils from the limed areas of the plots. 



Whether the action of the ammoniimi sulfate in the soil is one of double 

 decomposition between the ammonimn sulfate and calcium carbonate, or 

 in its absence some other salts, or whether the ammonia is first absorbed 

 physically, and the sulfuric acid thus set free reacts with the calcium, is 

 still a matter of dispute. While the results obtained do not prove either 

 of these theories to be correct, they seem to indicate that it maj^ be a com- 

 iDiuation of these two that takes place. 



The similarity between the absorption of annnonia and the absorption 

 of dyes is evidence that the ammonia is held by physical rather than chem- 

 ical forces. That it is not purely a chemical exchange is shown by the in- 

 creased amounts absorbed with the increased concentrations of the' solu- 

 tions used, and, as Voelcker and others have shown, all of the ammonia is 

 never absorbed from a solution, no matter how dilute. That some chem- 

 ical reaction takes place is shown by the amounts of calcium removed. 

 The amounts removed reach a definite limit, above which none is removed, 

 when the soil is shaken with a normal ammonium-sulfate solution. 



What takes place in soil fertilized with ammonimn sulfate may be as 

 follows: the first reaction to take place is the physical absorption of the 

 ammonia, thus setting free sulfuric acid. If, after the soil has absorbed 

 aU the aimnonia it is capable of holding, some ammonium sulfate remains, 

 double decomposition takes place. In both cases the first salt to be at- 

 tacked is probabty the calcium carbonate, and it is only in the al^sence of 

 this salt that the iron and almninium compounds are attacked. It is to 

 these salts of iron and aluminium that the infertility of the plots continu- 

 ously fertilized with sulfate of ammonia appears to be due. 



