Models for the field based toxicity of Cu and Zn salts to wheat in eleven Australian soils and comparisons to laboratory -based models.

Abstract

Relationships that can model and predict the phytotoxicity of metals according to soil physicochemical properties have recently been developed using laboratory phytotoxicity data. This paper presents the first relationships for field-based phytotoxicity data. Bread wheat (Triticum aestivum L.) was grown at eleven Australian field sites at which soil was spiked with copper (Cu) and zinc (Zn) salts. Toxicity was measured as inhibition of plant growth at 8 weeks and inhibition of grain yield at harvest. The EC10, EC20 and EC50 (grain yield) values for added Cu salt ranged from approximately 130 to 1130, 155 to 1560 and 210 to 5700 mg Cu/kg, respectively. The corresponding values for 8 week plant growth were 3 to 1100, 36 to 1130 and 220 to 2070 mg Cu/kg respectively. The EC10, EC20 and EC50 (grain yield) values for added Zn salt ranged from approximately 90 to 4760, 130 to 4775 and 260 to 4790, and mg Zn/kg, respectively. The corresponding values for 8 week plant growth were 17 to 2765, 75 to 3120 and 160 to 12 900 mg Zn/kg, respectively. Field and laboratory-based phytotoxicity data for short-term plant growth were not related for Cu but were for Zn, while there were no relationships between short-term (8wk) field-based biomass toxicity values and field-based harvest grain yield toxicity values. Field-based Cu toxicity (EC10 and EC20) for both endpoints was best modelled by relationships based on pH (measured in CaCl2) and the logarithm of organic carbon content while Zn toxicity (EC10, EC20 and EC50) for both endpoints was best modelled using pH and the logarithm of cation exchange capacity. Overall, the inclusion of background Cu and Zn concentrations in the relationships did not improve the ability of the relationships to describe the toxicity. The best relationships estimated toxicity within a factor of two of the measured values or produced estimates that were protective. Previously derived relationships derived for laboratory-based phytotoxicity data could not accurately model field-based phytotoxicity data.