A NEW SOIL TEST METHOD FOR THE DETERMINATION OF PLANT-AVAILABLE CADMIUM IN SOILS

A new soil test procedure using 1M NH4Cl was developed for the extraction of plant-available cadmium (Cd) from soils. Five grams of soil is weighed into a 50-mL polyethylene vial to which 30 mL, of 1M NH4Cl solution is added. The soil suspension is then shaken on a horizontal shaker for 16 h at 25 degrees C at 180 cycles per min. The suspension is then centrifuged at 2,500g for 5 min and the supernatant filtered through a 0.45 mu m nitrocellulose filter under vacuum. Cadmium in the extract is then determined at 228.8 nm on a graphite furnace equipped atomic absorption spectrophotometer. A highly significant correlation was observed between the natural logarithm (In) of 1M NH4Cl-extractable Cd in soils and the Cd content in the grain of durum wheat (Triticum turgidum var. durutn L.) grown on the same soils (r = 0.974, p = 3.8 x 10(-7)). In comparison with several commonly used extractants, such as ABDTPA, CaCl2, NH4OAc, and NH4NO3, the 1M NH4Cl- extracted Cd from soils was found to be a better index of Cd availability.