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Effect of Fertilizer Nitrogen on the Release of Soil Nitrogen¹

ABSTRACT

Some explanations which have been suggested to account for the stimulating effect of inorganic fertilizer nitrogen on the mineralization of organic soil nitrogen are examined; and new experimental evidence pertinent to their evaluation is presented.

Ionic exchange between fixed and exchangeable ammonium, and between exchangeable ammonium and amino-N was shown to be negligible. Rates of exchange resulting from biological activity were increased as a result of increasing the level of fertilizer N applied.

The stimulating effect was observed in soils receiving no organic amendment and in which no plants were grown indicating that it cannot be attributed solely to the activity of rhizosphere microflora. Osmotic effects appear to be a contributing factor.

¹ Contribution from the Department of Soils and Plant Nutrition, University of California, Davis. This work was supported by the National Science Foundation.

² Professor of Soil Microbiology.

Received for publication April 16, 1965. Accepted for publication June 30, 1965.