EFFECT OF SULFATE OF AMMONIA ON SOIL. 89 



the others. When the experiment was discontinued the seedUngs in the 

 extracts from the hmed end of plot 1 and plot 8 were the best, with the poor- 

 est in the extracts from the unlimed ends of plots 6 and 8. As the clo^'er 

 seedhngs did not make much growth they were omitted in the second 

 series and only barley was used. Barley was chosen, as it has been found 

 to be more sensitive to toxic substances than rye seedhngs. The filtered 

 extracts were also omitted, as no difference was noticeable between the 

 filtered and unfiltered extracts in the first series. 



As in the first series the second was continued four weeks. At the end 

 of the first week no differences were noticeable in the tops, but the roots 

 in the extract from the unhmed end of plot 6 again showed the stunted and 

 thickened appearance. At the end of two weeks the tops in the extracts 

 from the unhmed ends of the plots began to wilt, the tips of the leaves 

 turning white. Wlien the experiment was discontinued the seedlings in 

 the extracts from the hmed ends of the plots appeared just about ahke, 

 while in the extracts from the imhmed ends the poorest were the seedhngs 

 in the extract from plot 6. The seedhngs were weighed green, but the 

 weights did not show the differences which were apparent to the eye. 



When iron and aluminimn compounds were found in the soil it was 

 thought that these might have a toxic influence on plants, so culture work 

 was undertaken, using these salts. The results of this experiment have 

 already been pubhshed.^ It is only necessary to state that iron and alu- 

 minium salts are very toxic to clover seedhngs, and that in dilute solutions 

 calcium carbonate can overcome the toxicity. 



Summary and Conclusions. 



The results of the experiments show that — 



(a) The absorption of ammonia from sulfate of ammonia solutions by 

 the soils studied increases with the increase in the concentration of the 

 armnonium-sulfate solution used. This increase is not strictly proportional 

 to the increase in the concentration of the ammonium-sulfate solutions. 

 The soils from two plots pre\'iously fertihzed with ammonium sulfate 

 without hme absorb less ammonia than do the other soils. This shows 

 that the continued use of ammonium sulfate has caused some change in 

 the soil. 



(6) The absorption of dyes by these soils is veiy similar to the absorp- 

 tion of ammonia. More dye is absorbed from the more concentrated so- 

 lution than from the lesser concentration. The two unlimed sulfate plots 

 also absorb less than do the others, showing that their absorptive powers 

 have been lessened. 



(c) Ammonium sulfate has a solvent action on the calcium in the soils, 

 and depletes the soil of this element. This is shown by the ammonium- 

 suKate extracts and also by the drainage water anal5^ses. 



(d) Ammonium sulfate seems to have no solvent action on sodium or 

 potassium in the soil in the presence of sufficient quantities of Ume. That 



» Bui. 161, Mass. Exp. Sta., 2d part. 



