Phytotoxicity and microbial respiration of Ni‐spiked soils after field aging for 12 yr

To assess the impact of Ni toxicity in soils after long‐term field aging, a coarse‐textured soil was spiked with Ni salt at 100, 200, and 400 mg kg −1 Ni concentrations. These soils were aged in the field along with an unspiked (control) soil under natural conditions for 12 yr, after which total soil Ni was measured and tests of Ni extractability by 0.01 M CaCl 2 and diethylenetriaminepentaacetic acid (DTPA) were done. Soybean assays and soil respiration tests were performed to determine residual Ni toxicity of the aged contaminated soils. The greatest loss of Ni after 12 yr of aging occurred from the soil spiked with the highest Ni level, but substantial loss of Ni occurred from the lower Ni levels as well. Loss was attributable to leaching as the fraction of readily extractable (by 0.01 M CaCl 2 ) Ni diminished with long‐term aging. Readily extractable and DTPA‐extractable Ni increased with increasing soil spiking levels, but only the latter was linearly proportional to total Ni. Phytotoxicity to soybeans ( Glycine max L.) in the field was initially high at all levels of added Ni but diminished over the 12 yr of aging. A greenhouse soybean assay with the 12‐yr aged soils confirmed toxicity to be statistically significant at all Ni addition levels and dose‐dependent, with 0.01 M CaCl 2 ‐extractable Ni >5 mg kg −1 shown to be measurably phytotoxic to soybeans. Phytotoxicity may have been caused at least in part by the observed inhibition of Mn, Fe, Cu, and Zn uptake by soil Ni. Soil respiration was increasingly inhibited as levels of added Ni increased from 100 to 400 mg kg −1 . Environ Toxicol Chem 2018;37:1933–1939. © 2018 SETAC