Kinetics of Soil Potassium Release Under Long-Term Imbalanced Fertilization in Calcareous Soils

Knowledge on potassium ion（K~＋） release from soils makes K fertilizer recommendation more efficient and profitable.Kinetics of K~＋release under continuous fertilization of no fertilizer（CK）, urea（N）, triple superphosphate（P）, and urea ＋ triple superphosphate（NP） without K fertilizer was investigated in calcareous（chloritic and kaolinitic） soils on the Miandarband Plain in Kermanshah Province of Iran.The results showed that the kinetics of K~＋release included an initial reaction and a slow reaction.The phosphateand NH_4~＋-induced K~＋release followed the same rate process during the rapid（2–192 h） and slow release periods（192–1 090 h）.There were no significant differences in the cumulative K~＋released from the chloritic and kaolinitic soils among all the treatments.The cumulative K~＋released was positively correlated with P adsorption capacity for the chloritic（r = 0.461, P 〈 0.05） and kaolinitic soils（r = 0.625, P 〈 0.01）, and negatively correlated with K fixation potential for the chloritic（r = 0.720, P 〈 0.01） and kaolinitic soils（r =-0.513, P 〈 0.01）.There was a significant（P 〈 0.001） interactive effect of K fixation potential × P adsorption capacity on the cumulative K~＋released for both soil groups.The initial release rate（IRR） index（a·b, where a and b are the rate coefficients of the power function equation） for the chloritic soils was significantly（P 〈 0.05） higher under applications of P and NP than N and CK.The IRR index values among different fertilization treatments were in the order of NP = P 〉 N = CK for the chloritic soils, and N =P 〉 NP 〉 CK for the kaolinitic soils.This study showed that K fixation potential and P adsorption capacities controlled K~＋release from soils.This information will be helpful for precise fertilizer recommendations for the studied soils.