Effects of liming and selected heavy metals on ammonium release in waterlogged agricultural soils

Abstract

Many farmlands are periodically flooded or ponded by excessive precipitation resulting in changes to soil chemical and biochemical properties. In this study, one set (eight treatments with four replications) of field-moist surface soils (0–15 cm) and their air-dried counterparts obtained from a long-term liming experiment were incubated at 30 °C under waterlogged conditions for 10 days, and the amounts of net NH4+-N released (soluble and exchangeable) were determined after extraction with 4 M KCl. Another set of three surface soils were used to evaluate the effect of six heavy metals on the NH4+-N release under waterlogged conditions. Results showed that increasing the liming rate from 0 to 17,930 kg ha−1 effective calcium carbonate equivalent increased the average soil pH from 4.98 to 7.06, averages of the amounts of NH4+-N released ranged from 1.6 to 5.2 mg N kg−1 field-moist soil, and the corresponding amounts released in air-dried soils ranged from 18.9 to 32.9 mg N kg−1 soil. This increase of the amount NH4+-N released in air-dried soil samples is presumably due to a slaking effect. At 5 mmol kg−1 soil, all six heavy metals inhibited the NH4+-N released. The relative effectiveness of the heavy metals in inhibition of the NH4+-N released varied among the three soils. Lead(II) was the most effective inhibitor of NH4+-N release in Clarion and Harps soils and Cd(II) in Harps soil. Cobalt(II), Cu(II), and Cd(II) were the least effective inhibitors of NH4+-N release in Clarion, Harps, and Okoboji soils, respectively.