Effects of chicken manure and peat on Cr(VI) uptake in a soil–plant system: Cr fractionation and plant physiological responses

Abstract This study was conducted to investigate the effects of natural organic soil amendments (chicken manure (CM) and peat (PE)) on Cr(VI) uptake in a soil–plantsystem. CM and PE (20 mg/kg) were added to soil with 100 mg/kg Cr(VI). Pharbitis purpurea (P. purpurea) was planted in the treated soil. The fractionation of Cr(VI) in soil was analyzed after 7, 21 and 35 days, and plants were collected on the 35th day for determination of Cr(VI) concentration and plant growth physiological indexes. The results showed that Cr(VI) accumulation in P. purpurea was most significantly reduced by CM to only 67.1% of the control group (CK) (394.8 mg/kg). Conversely, the PE treatment promoted Cr(VI) accumulation in the plants, which was 1.13 times higher than that in the CK. CM reduced Cr(VI) accumulation in P. purpurea by decreasing the bioavailable Cr(VI) fractions in the soil to 65.5% of those of the CK. In addition to chemical fractionation, the plant and its physiological conditions also affected Cr(VI) uptake. PE amendment significantly promoted plant physiology and growth, with the biomass and root length of P. purpurea being 2.10 and 2.16 times higher than those of the CK, respectively. Therefore, Cr(VI) uptake is a balance of reduced bioavailability and enhanced plant growth. CM decreased Cr(VI) mobility in the soil and then alleviated Cr(VI) stress on the plant, whereas PE increased the Cr(VI) stress tolerance of the plants and improved their absorption ability. Both PE and CM can be used as efficient soil amendments for Cr(VI)-contaminated soil.