EFFECT OF SULFATE OF AMMONIA ON SOIL. 83 



A third method, taking a solution of calcium sucrate, was also used. 

 Ten grams of soil were shaken with 50 cubic centimeters of the solution, 

 filtered after two hours and an aliquot titrated. Two strengths of the 

 caleium-sucrate solution were used, — a saturated solution and another 

 one-tenth as strong. The absorption of calcium was the same with both 

 solutions and on both the limed and unlimed areas. The absorption was 

 much greater than \vith either of the two previously mentioned methods. 

 The unlimed end absorbed at the rate of 26,660 pounds of calcium oxide 

 per acre, while the limed end absorbed at the rate of 23,850 pounds per 

 acre. The greater absorption of the calcium from the sucrate solutions is 

 due to the greater concentration of calcium in these solutions. The 

 Veitch method does not measure the true absorptive capacity of the soil, 

 but measures the absorption up to the point of alkaUnity of the soil. That 

 the soil can absorb more calcium after the point of alkalinity is reached is 

 shown by the results obtained by the other methods. With the caleium- 

 sucrate solution the Umit of the amount of calcium which the soil can 

 absorb seems to have been reached, as with an increase in the concentra- 

 tion no increase in the amount of calcium absorbed is noted. 



It is of interest to compare the results obtained by the above methods 

 vnth the calcium oxide equivalent obtained with the Hopkins method of 

 determining soil acidity. With this method a marked difference between 

 the hmed and unhmed areas of plot 6 is found. The unUmed area has a 

 much higher calcium oxide equivalent than the hmed area. The calcium 

 oxide equivalent of the hmed end is 631 pounds of calcium oxide per acre, 

 while the unhmed gives an equivalent of 4,976 pounds per acre. 



This "acidity," however, is not due to the presence of free acids, either 

 soluble or insoluble in water, but is probably due to the presence of iron 

 and aluminimn salts. When the soils are shaken up with the normal 

 potassium-nitrate solution, as the method calls for, an action resembhng 

 a double decomposition takes place between the iron and aluminium 

 compounds and the potassium nitrate, with the formation of the easily' 

 hydrolyzable iron and aluminium nitrates which go into solution. When 

 the aliquot is titrated the titration shows the amount of nitric acid present 

 in combination with iron and aluminium, as is evidenced by the heavy 

 flocculent precipitate which forms during the titration. In order to de- 

 termine if nitrates of iron and aluminium hydrolyze readily, known solu- 

 tions of those salts were made up and titrated. It was found that the 

 entire quantity' of nitric acid present could be titrated. 



Summarizing the results obtained by the different methods, we find 

 that the soil absorl^s increasing amounts of calcium from increasing con- 

 centrations of calcium solutions, and that the limed and unlimed plots 

 absorb practically like amounts of actual calcium. 



