Changes in Characteristics Related to Copper Release in Wheat (Triticum aestivum. L) Rhizosphere in Some Calcareous Soils

Rhizosphere is a small zone with chemical، physical، and biological properties different from those of the bulk soil. Information regarding the kinetics of Cu release in the rhizosphere soil is scant. Throughout this research، kinetics of Cu release was investigated in wheat crop rhizosphere vs. non-rhizosphere in 10 calcareous soils by use of rhizobox and in greenhouse conditions. Extracts from rhizosphere and non-rhizosphere soil samples were obtained through successive extraction with DTPA-TEA for 1 to 504 h at 25±1 oC. The available Cu was assessed using chemical extractants (DTPA-TEA، AB-DTPA and Mehlich 3). The results indicated that the level of Cu extracted by chemical extractions from the rhizosphere was lower than those extracted from the nonrhizosphere soils. Also، the level of cumulative released Cu from the rhizosphere was significantly (P<0. 05) lower than that in the non-rhizosphere soils. In the rhizosphere soil، the released Cu ranged from 4. 88 to 10. 66 mg kg-1 while in the non-rhizosphere soils it ranged from 6. 38 to 12. 08 mg kg-1. The results also indicated that parabolic diffusion; first order and power function equations could be employed to describe the kinetics of Cu release. In addition، the rate of Cu release from the rhizosphere soils was also lower than that from the non-rhizosphere soils. In the rhizosphere and non-rhizosphere soils، the characteristics of Cu release were significantly correlated (P<0. 05) with Cu extracted when using chemical extractants. Moreover rate constant coefficient in parabolic diffusion was significantly correlated (P<0. 05) with concentration of Cu in wheat shoot in the rhizosphere area of soils. The results illustrated that characteristics of Cu release in the rhizosphere are different from those in the non-rhizosphere area in soils.