Optimizing ammonium acetate procedure for determining available potassium in Iranian calcareous soils, testing the concentration and contact time

Ammonium acetate (NH4C2H3O2) is the extractant mostly used by the local soil laboratories in Iran when determining available potassium (Kava) in calcareous soils. To optimize the procedures for determining soil available potassium (Kava), two individual experiments were carried out.For this purpose, the effect of two NH4OAc concentrations (i.e., 1 M and 0.1 M NH4OAc) and  the efficiency of two extraction procedures (i.e., 30 min shaking on the orbital shaker and keeping the mixture overnight (12 h) without shaking) were investigated. Calcareous soils (1234 samples) from different parts of Iranian provinces were collected. The results revealed that in most soils, the decrease in the NH4OAc concentration from 1 to 0.1 M had no significant effect on the Kava concentration. There was a significant and positive correlation between potassium concentrations of 1 and 0.1 M NH4OAc extractants, although, a significant deviation was observed for some soils. The regression equation between the two extractants was y = 0.97 x + 8.43 (R2 = 0.97 and SEE = 36.5), which overlaps with the 1:1 line. Therefore, to save the chemicals and reduce analysis costs, 0.1 M NH4OAc can be used instead of 1 M NH4OAc. Results obtained from the second experiment clearly showed that shaking the mixture for 30 min was as effective as keeping it overnight without shaking to 30 min with shaking in extracting soil available potassium.