Potassium (K) exchange isotherms (quantity-intensity technique, Q/I) and K values derived from the Q-I relationship provide information about soil K availability. | Turk J Agric For 30 (2006) 213-222 © TÜB‹TAK Potassium Exchange Isotherms as a Plant Availability Index in Selected Calcareous Soils of Western Azarbaijan Province, Iran Abbas SAMADI Soil Science Department, Urmia University, . Box 165, Urmia, 57134, . IRAN Received: Abstract: Potassium (K) exchange isotherms (quantity-intensity technique, Q/I) and K values derived from the Q-I relationship provide information about soil K availability. This investigation was conducted to study the relationships among K Q/I parameters, available K extracted by 1 N NH4AOc (exchangeable K plus solution K), potassium saturation percentage (K-index, %), and the properties of 6 different calcareous agricultural soils. In addition, the relationship of tomato plant yield response to the K requirement test based on K exchange isotherms was investigated. The Q/I parameters included readily exchangeable K (∆K0), K specific K sites (KX), linear potential buffering capacity (PBC ), and energy of exchange of K (EK). The results of X-ray diffraction analysis of the oriented clay fractions indicated that some mixed clay mineral, some chlorite/illite clay minerals, along with palygorskite and kaolinite were present in the soils. The soil solution K activity ratio at equilibrium (AR0) ranged from to -1 0 -1 (moles l ) . The readily exchangeable K (∆K ) was between and (cmolc kg soil), which represented an average of 51% of the exchangeable K (Kex). There was a significantly positive relationship between ∆K0 and NH4AOc-extractable K (r = 98, P (Sparks and Liebhardt, 1981). The AR0 values have significant relationships with labile K (∆K0) and NH4AOc-extractable K (Table 3). There was no relationship between AR0 and the ability of any of the studied soils to supply K over an extended period of K time (PBC ). This result is in agreement with that obtained by Alafifi (1996) for the calcareous soils of the United Arab Emirates. The labile K (∆K0) values
