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Nitrogen Immobilization in Flooded Soils¹

ABSTRACT

Nitrogen immobilization in flooded soils amended with straw was measured by following incorporation of tagged inorganic N into the soil organic fraction. Increases in tagged organic N were found to be highly correlated with net immobilization as measured by decrease in mineral nitrogen in the soil. Since most of the soils used contained clay minerals capable of ammonium fixation, apparent immobilization figures were corrected by subtraction of clay-fixed ammonium.

In comparisons of nitrogen immobilized under different soil conditions it was found that values obtained in flooded soils were intermediate between those obtained under aerobic and anaerobic conditions. The nitrogen factor, or additional N immobilized, per unit weight of straw, was found to vary with quantity of straw added, nitrogen content of the straw, and nature of the soluble nitrogen supplied, but in no case was it negligible. Rice straw (Oryza sativa L.) containing 0.47% N immobilized an additional 0.51% N in a flooded soil, and another sample of rice straw containing 1.17% immobilized 0.43% N.

¹ Contribution from the Department of Soils and Plant Nutrition, University of California, Davis. The research of this project was conducted in cooperation with the Tennessee Valley Authority.

² Professor of Soil Microbiology and Laboratory Technician, respectively.

Received for publication April 25, 1969. Accepted for publication October 14, 1969.