Manganese in soils: speciation and toxicity to plants.

Abstract

Manganese speciation andt toxicity of Mn to barley was assessed in three soils. A 50 percent yield reduction occurred at a shoot concentration of circa 4000 mg/kg, which was reached at a soil solution of circa 500 mg Mn/L or total Mn concentration in soil between 500 (low pH) and 2500 mg/kg (high pH soil). Waterlogging had no effect on Mn speciation in the low pH soil (pH 4.7) where Mn was mainly as MnII, but reduced the Mn oxidation state, from MnIII/IV to MnII, and increased the solubility of Mn in the soils with pH>6 at background Mn. However, in soils spiked with MnCl2, the added Mn remained for a large part as MnII, even under aerobic conditions, explaining why waterlogging had little effect on the toxicity of Mn