Manganese concentrations in soil and wheat crops were monitored over time in the field.

• Six sites in north-east Victoria on acid duplex soils were sampled monthly to monitor manganese concentrations in soil and weed crops in relation to changing seasonal conditions.
• Cool and/or moisture conditions were associated with exchangeable manganese of less than 50 ppm.
• High concentrations of exchangeable manganese (120 – 250 ppm) were associated with waterlogging or prolonged hot dry conditions.
• The rate of increase in exchangeable manganese was greatest under waterlogged conditions in winter there was a lack of more than one month before significant increases were observed.
• Manganese concentrations in wheat tops reached 800 – 1200 ppm at the 3 sites most severely waterlogged during 1981.
• At the better drained sites the concentrations were less than 400 ppm.
• It seems that high levels of exchangeable manganese during summer have little effect on subsequent wheat crops.
• Waterlogging may result in increased concentrations of plant manganese but perhaps only in young plants or after prolonged exposure, by which time other effects of waterlogging may already have severely limited growth.