Influence of added manganese on nitrification in a low-manganese soil

Summary

Nitrification was studied in a Leefield sand, sufficiently low in Mn to produce severe Mn deficiency in soybeans. The soil was treated with 100 μg/g NH₄ ⁺-N, 0, 10, 100 and 1000 μg/g Mn, and incubated at field capacity for six weeks at 30°C. Weekly determinations of (NO₃ ^-+NO₂ ^-)-N and NH₄ ⁺-N revealed that nitrification was not increased above the control level by any of the Mn rates. In the control, the decrease in soil pH associated with nitrification caused an increase in extractable Mn from 0.12 to 1.56 μg/g during the experimental period. The 1000 μg/g rate of Mn completely inhibited nitrification for the first five weeks of the experiment, but nitrification began to occur during the sixth (last) week. It is postulated that Mn was being converted to unavailable forms such that by the sixth week the level of active Mn had been reduced sufficiently to permit nitrification to begin. re]19760512