Manganese toxicity to peanuts in autoclaved soil

The interveinal leaf chlorosis occurring in Argentine peanuts growing in autoclaved soil is the result of manganese toxicity. The toxic level of manganese results from two mechanisms: the direct release of manganese complexed with the organic fraction of the soil, and the killing of microorganisms that normally transform available manganese into higher oxides. Propylene oxide treatment of soil resulted in a gradual increase in available manganese but selectively blocked microbial conversion of divalent Mn to a nonavailable state. Methyl bromide had no measureable effect.