Measurement and Interaction of Soil Phosphorus, Cadmium, and Zinc using Quantity-Intensity Desorption Isotherms

Phosphorus (P), cadmium (Cd), and Zinc (Zn) are closely related in the agricultural environment. Information about P, Cd, and Zn desorption quantity intensity (Q/I) relationships in soil is useful for environmental evaluations and for studying those elements. The objectives of the methodological study were to develop and to propose an anion-exchange resin membrane disk method to determine soil P desorption Q/I relationships. The objectives of the P, Cd, and Zn interaction study were to determine the effect of P and Zn treatments on Zn and P availability and to estimate the influence of Cd and Zn treatments on Zn and Cd availability using desorption Q/I isotherms. In the methodological study, soil samples were enriched which four P concentrations applied as KH2P04 solution, incubated at field capacity, and then equilibrated with different amounts of bicarbonate (HCO3-) - saturated anion-exchange resin membrane disks connected into a chain and resin beads in a mesh bag . After equilibration, resin extractable Pas a quantity factor (Q) and soil solution Pas an intensity factor (I) were determined. The amounts of P extracted by the resin membranes from the soils were similar to those extracted by the resin bead bags even though the exchange capacity of resin membrane was much lower than that of the resin bead bag. The equations of Q=a+bIC and Q=aI-0.1 +bln (I+l) +c plotted very similar curves and were suitable to describe P desorption Q/I curves and to determine buffering power (IBPol) . The resin membrane dis k method is closely related to the resin bead bag method, and the resin membrane behaves in a similar manner to the resin bead. In the P, Cd, and Zn interaction study, soil samples were enriched with different concentrations of P, Cd, and Zn as KH2PO4. CdCl2, and ZnSO4 solutions, and incubated at field capacity. Zinc enrichments only affected availability of Pin Egan soil, which contains higher amounts of clay, organic matter, and exchangeable Fe. The influences of P or Cd treatments on Zn availability were varied, whereas the effects of Zn treatments on Cd availability were more uniform. The Zn buffering capacity, BCzn, as affected by P treatments ranged from 202 to 4480 and were lowest in the Egeland soil that involved lowest soil pH, amounts of clay minerals, organic matter, CEC, and exchangeable Fe, whereas the BCzn values were highest in the calcareous Glenham soil. The BCzn values as affected by Cd treatments ranged from 145 to 4480, decreased with increasing Cd enrichments in Egan and Egeland soils, and increased with Cd enrichments in Glenham and Maddock soils. The changes of DTPA-extractable Zn (Q) and water-extractable Zn (I) were found to be dependent upon soil properties, especially, soil pH. The Cd buffering capacity, BCcd, affected by Zn treatments ranged from 206 to 2256, and decreased with increasing Zn enrichments in all soils. In the calcareous Glenham soil, Zn is relatively more available than Cd, whereas in Egan, Egeland and Maddock soils, availability of Cd is higher than that of Zn