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Phytotron Experiments to Evaluate the Effect of Growing Plants on Denitrification¹

ABSTRACT

The amount and availability of plant rhizosphere carbon deposits and their influence on microbial denitrification in soil are not clearly defined. To evaluate this possibly important facet of fertilizer N loss from agricultural soils a study was conducted to simultaneously quantify the carbon fixed by plants and the fate of fertilizer nitrogen applied to the soil during a plant growing season. Corn (Zea mays) or wheat (Triticum aestivum) was grown in a phytotron under a continuous supply of ¹⁴CO₂ in ¹⁵N fertilized soil. The results of the studies show that denitrification was not stimulated in soils planted with corn or wheat compared to unplanted soil. About 60% of the root biomass carbon could be found in the soil as rhizodeposited carbon at the termination of the experiments. Only 5 to 7% of this carbon was, however, extractable with water or 2 M Na₂SO₄. This suggests that even though a sufficient quantity of carbon was deposited in the soil by the plants that the carbon was not available for denitrification.

¹ Contribution from the Federal Agricultural Research Center, Braunschweig, Federal Republic of Germany and USDA-ARS, P. O. Box E, Fort Collins, CO 80522.

² Research Chemist, Institute for Plant Nutrition & Soil Science, Federal Agricultural Research Center, Braunschweig, Federal Republic of Germany, research chemist, USDA-ARS, P.O. Box E, Fort Collins, CO 80522, and research microbiologist, Inst. of Soil Biology, Federal Agricultural Research Center, Braunschweig, Federal Republic of Germany, respectively.

Received for publication September 13, 1984. Accepted for publication January 7, 1985.