Comparision of Different Methods of Gypsum Determination in Selected Soils from Isfahan

Gypsum affects many physical, chemical and mineralogical properties which in turn influences management, classification and sutability of the soils. This is the reason why accurate measurement of gypsum in soil is very important. In most of the soil science laboratories, the method of acetone ,in spite of its too much limitation, is being used as a standard method. The purpose of this research was to compare different gypsum determination methods and to find the most suitable one. The study areas include Jafarabad of Borkhar and Sepahanshahr.Soil samples were collected from different horizons of the studied profiles and seven samples with a wide range of gypsum content were selected. Gypsum content of the soil samples were determined by methods of acetone, sodium carbonate, resin, calcium and magnesium difference, diluted extracted sulfate, ammonium carbonate, sodium citrate and hydrochloric acid. To calculate the recovery percentage of the methods, after adding a certain amount of gypsum with known purity percentage to the soil samples, gypsum content was determined again by above mentioned eight methods. To evaluate the suitability of the methods, in addition to the recovery percentage of the methods, coefficient of variability and extent of proximity of the regression line to the 1:1 line were used. The results revealed that among the used methods, the method of sodium carbonate is the most accurate one. Resin method is ranked as the second best method and can be used in non-saline soils as another accurate method for determination of gypsum content. Sodium citrate and hydrochloric acid methods for different amounts of gypsum and ammonium carbonate method for gypsum content up to 30% are third in rank as far as their accuracy is concerned. Acetone, calcium magnesium difference and diluted extracted sulfate methods are not sufficiently accurate, because of low solubility of gypsum in water which is used as an extractant. In general, the most important determinant of accuracy of the methods is extractants of the gypsum among which the sodium carbonate has the highest efficiency.