تأثیر لجن فاضلاب بر جذب فسفر و فسفر قابل استفاده در برخی از خاک‌های آهکی

Organic manures can affect phosphorus (P) sorption characteristics (PSC) and its availability in soils. Information about effect of sewage sludge (SL) on PSC in calcareous soils of Hamadan province is limited. The objective of this research was to study the effect of SL on PSC and available P in 10 calcareous soils. The soil samples were incubated with and without 1.5 % SL for 5 months at field capacity at 25 ±1 סC . After incubation, available P was determined by Olsen method. Furthermore, 2.5 g samples were shaken with 25 mL 0.01 M CaCl2 containing 0 to 30 mg P L-1 as KH2PO4. After equilibration, suspensions were centrifuged and P concentration was determined in clear extracts. The results showed that SL application increased available P. The mean available P value increased by 37.6 %. Available P in untreated and SL-treated soils ranged from 8.1 to 22.1 and 14.8 to 28.0 mg kg-1, respectively. Sorption data in the all samples were well described by Freundlich and linear isotherm, whereas sorption data in all SL-treated soils did not adequately fit to the Langmuir isotherm. The constants of sorption isotherms were lowered by SL application. The mean sorption maxima, binding energy and maximum buffering capacity values decreased by 38.85, 21.34 and 38.90 % respectively. The mean distribution coefficient, Freundlich n and the mean buffering capacity (slope of linear model) values decreased by 21.7, 16.0 and 6.1 %, respectively. The results of this study showed that application of SL decreases standard phosphorus requirement. Moreover PSC results indicated that use of sewage sludge might increase the risk of P transfer to surface water.