Effects of Organic Carbon, Active Calcium Carbonate, and Clay on Phosphorus Sorption Properties in Some Calcareous Soils of Kerman Province

Phosphorus availability in soils is controlled by sorption/desorption reactions. These reactions are also affected by the physical and chemical properties of the soil. In this research, effects of organic carbon, active calcium carbonate and clay on the phosphorus sorption behavior of calcareous soils were studied along Negar-Lalezar and Baft Orzouyeh transects in Kerman Province, Iran. The phosphorus sorption in soil was determined using batch experiment and Langmuir, Freundlich and Van Hay isotherms. The results showed that, based on the coefficient of determination (0.978) and standard error of estimate (0.027), Langmuir model fitted well with experimental data. Maximum sorption of phosphorus (qmax) and maximum buffering capacity of P increased when the active calcium carbonate increased. Results showed that qmax increased from 655 to 1025 mg.kg-1, and the maximum buffering capacity of P increased from 114 to 243 L.kg-1 when calcium carbonate increased from 7.68% to 18.25%. However, qmax decreased from 701 to 535 mg.kg-1 and maximum buffering capacity of P decreased from 90 to 44 L.kg-1 with increasing organic carbon in the studied soils (from1.74% to 7.8%). Using the equation of Van Hay, the required standard phosphorus calculated at a concentration of 0.3 mg P.L-1 showed a significantly positive correlation with clay (r = 0.80**) and active calcium carbonate (r = 0.77**) contents, but significantly negative correlations with organic carbon (r = -0.63*) and available phosphorus (r = -0.61*). The maximum buffering capacity and the required standard phosphorus were found in the soils of Orzouyeh and Negar regions due to their highest percentage of active calcium carbonate and clay. However, in the soils of Lalezar and Baft regions, due to the presence of more organic carbon and less active calcium carbonate, the lowest standard phosphorus requirement was obtained. It could be concluded that phosphorus sorption in soils is influenced by soil properties such as clay, active calcium carbonate, and organic carbon contents.