INFLUENCE OF AMMONIUM NITROGEN ON NITROGEN FIXATION IN PADDY SOILS

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Abstract
We studied the influence of ammonium sulfate on heterotrophic nitrogen fixation in four paddy soils under two water treatments, employing acetylene reduction assay. In alluvial, laterite, and acid saline (Karapadam) soils amended with cellulose, more nitrogen fixation occurred under nonflooded conditions (60 percent water-holding capacity) than under flooded conditions. In submerged soils, nitrogen fixation decreased with increasing concentrations of ammonium sulfate; under nonflooded conditions, this inhibition was more pronounced. The alterations in the acetylene reduction activities were attributed to the differential degree of organic matter decomposition under the two water regimes. The maximum acetylene reduction was noticed during the 9 to 12-day incubation irrespective of water regime. Low concentrations (5 to 20 ppm) of added N stimulated nitrogen fixation, though higher concentrations were inhibitory. Nitrogen fixation in acid soils was lower than in alluvial and laterite soils. We studied the influence of ammonium sulfate on heterotrophic nitrogen fixation in four paddy soils under two water treatments, employing acetylene reduction assay. In alluvial, laterite, and acid saline (Karapadam) soils amended with cellulose, more nitrogen fixation occurred under nonflooded conditions (60 percent water-holding capacity) than under flooded conditions. In submerged soils, nitrogen fixation decreased with increasing concentrations of ammonium sulfate; under nonflooded conditions, this inhibition was more pronounced. The alterations in the acetylene reduction activities were attributed to the differential degree of organic matter decomposition under the two water regimes. The maximum acetylene reduction was noticed during the 9 to 12-day incubation irrespective of water regime. Low concentrations (5 to 20 ppm) of added N stimulated nitrogen fixation, though higher concentrations were inhibitory. Nitrogen fixation in acid soils was lower than in alluvial and laterite soils. © Williams & Wilkins 1981. All Rights Reserved.