HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Stanford, G. Articles by Dzienia, S. Search for Related Content PubMed Articles by Stanford, G. Articles by Dzienia, S. Agricola Articles by Stanford, G. Articles by Dzienia, S.

Denitrification Rates in Relation to Total and Extractable Soil Carbon¹

ABSTRACT

Denitrification rates were studied under near-anaerobic conditions in 30 soils of diverse origin that differed widely in pH, organic C contents, and other characteristics. Soils with added NO₃-N were submerged in water and containers were sealed to prevent further oxygen intake during incubation. Disappearance of NO₃-N and production of NH₄-N were determined at 1-day intervals or longer over a 10-day period. Since soils were not shaken during incubation, denitrification rates were influenced by diffusion of nitrate from the liquid to the soil layer. In most soils, amounts of NO₃-N declined exponentially with time of incubation. Thus, under the experimental conditions, the loss of nitrate was depicted better by log NO₃-N vs. time (t, hours) than ppm NO₃-N vs. t. The apparent first-order rate constants (k), denoting the fractional loss of NO₃-N/hour, ranged from about 0.001 to 0.04 hour^-1. Correlations of k with total soil organic C and with soil "glucose-C," extracted by boiling soils for 1 hour in 0.01M CaCl₂, were highly significant. However, the extractable glucose-C (an index of readily decomposable C sources) provided a more reliable basis for predicting k than did total organic C. The regression of k on glucose C (X) for 30 soils is as follows: k = 0.188X – 0.00093, (r² x 100 = 82%). For the corresponding regression involving total organic C, r² x 100 = 69%. Within 24 to 48 hours, appreciable amounts of Mn appeared in solution and usually continued to increase with time. Reduced Fe did not appear until most of the NO₃-N had disappeared. After 48 hours of incubation, the multiple regression of Mn (Y), in solution, on NH₄-N produced (X₁) and initial soil pH (X₂), with associated statistics, was as follows: Y = 13.8 + 3.5X₁ – 13.5X₂ (R = 0.77), r_Y1.2 = 0.48. Values are significant at the 1% level.

¹ Contribution from the Plant Physiology Institute and the Agricultural Research Service, USDA, Beltsville, Maryland 20705.

² Research Soil Scientist and Biologist Lab Technician, ARS, USDA, Beltsville, Md., and IREX Scholar (International Research and Exchanges Board), Academi of Agriculture, Inst. of Soil and Plant Cultivation, Szczecin, Poland.

Received for publication August 2, 1974. Accepted for publication November 26, 1974.