EFFECT OF SULFATE OF AMMONIA ON SOIL. 75 



125 pounds of potash. The only organic matter added has been in the 

 form of crop residues and catch crops plowed under. Hydrated hme was 

 applied to one-half of the field at the rate of 3,000 pounds per acre in 1909, 

 and again in 1913, when the rate of application was 4,000 pounds. The 

 apphcation was made crosswise of the plots so that every plot was half 

 limed and half imlimed. 



The first soil samples were taken from these plots in 1912, just before 

 the fertilizers were appHed and after the land had been plowed. The 

 second set of samples was taken in the spring of 1913, immediately after 

 the lime had been applied and harrowed in, but before the apphcation of 

 any fertilizers. The soils were taken to the laboratory as soon as sampled, 

 thoroughly mixed and air-dried. In subsampling, the soil was passed 

 through a sieve having seven holes to the linear inch. No finer sieve was 

 used, as it was desired to have the soil in as nearly actual field condition as 

 possible. 



The crops growTi in the years previous to the sampling (1911 and 1912) 

 were corn with clover sown in the corn during the fall. The crops were 

 the same both years, as the clover made a poor catch in 1911 and was 

 plowed under. 



Method of Investigation. 



A large part of the investigation was carried on with different strengths 

 of ammonium-sulfate solutions. The four strengths used most were one- 

 tenth normal (N/10), normal (N), two and one-half times normal (2,^ N) 

 and five times normal (5 N). 



Unless otherwise stated the soil was treated as follows: 150 grams of 

 air-dried soil were treated with 750 cubic centimeters of the ammonium- 

 sulfate solution. The mixture was allowed to stand, with frequent shak- 

 ings, for two hours, and then filtered through an miwashed filter paper. 

 In every case the filtrate was perfectly clear but j^eUow, the intensity of 

 the color varying between the limed and unlimed soils and with the strength 

 of the solution used. The solutions were all neutral to htmus and phe- 

 nolphthalein. 



The solutions were analyzed for the amount of ammonia absorbed, and 

 for the iron and aluminium, calcium, sodium, potassium, sulfates, chlo- 

 rides and nitrates removed. 



Absorption of Ammonia. 

 The ammonia was determined by the magnesimn oxide method. ^ From 

 1 to 10 cubic centimeters of the solutions were used for a determination, 

 depending on the concentration of the solution. Table II. gives the 

 amounts in milhgrams of the anmionia absorbed by 100 grams of air-dried 

 soil. 



» Bui. 107, Bureau of Chem., p. 9, 1910 edition. 



