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 

 calcium-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 with either of the two previouslj^ mentioned methods. 

 The unhmed end absorbed at the rate of 26,660 pounds of calciimi oxide 

 per acre, while the Umed end absorbed at the rate of 23,850 poimds 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 measm-es the absorption up to the point of alkalinity 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 calcium- 

 sucrate solution the hmit 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 calciimi 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 limed and unhmed areas of plot 6 is found. The unlimed area has a 

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

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

 while the unlimed 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 aluminium salts. When the soils are shaken up with the nonnal 

 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, wdth the fonnation of the easily 

 hydrolyzable iron and aluminium nitrates which go into solution. When 

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

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

 fiocculent precipitate which fonns during the titration. In order to de- 

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

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

 entire quantitj^ of nitric acid present could be titrated. 



Summarizing the results obtained by the different methods, we find 

 that the soil absorbs increasing amounts of calcium from increasing con- 

 centrations of calcimn solutions, and that the hmed and unlimed plots 

 absorb practically like amounts of actual calcium. 



