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|Title:||Evolution of Dinitrogen and Nitrous Oxide From Soils Treated With Nitrogen-15-Labeled Fertilizer|
|Author(s):||Mulvaney, Richard Lesley|
|Department / Program:||Agronomy|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Although it was demonstrated nearly a century ago that soil contains denitrifying microorganisms capable of reducing nitrate (NO(,3)('-)) to dinitrogen (N(,2)) and nitrous oxide (N(,2)O), the significance of denitrification under field conditions is still largely unknown because of difficulties associated with its measurement. These difficulties arise from the fact that one of the products (N(,2)) is the major constituent of air.
Recent work in our laboratory has led to the development of a procedure that permits analysis of natural atmospheric samples for N(,2) evolved during denitrification in soils treated with ('15)N-labeled fertilizer. This procedure involves the use of liquid N(,2) and commercial O(,2) traps for purification of the gas sample and measurement of the ratios, r = ('29)N(,2)/('28)N(,2) and r' = ('30)N(,2)/(('28)N(,2) + ('29)N(,2)), with a dual-inlet ratio mass spectrometer.
The objectives of the work reported were: (i) to develop a mass spectrometric procedure for determination of ('15)N-labeled N(,2)O which could be used in conjunction with the procedure previously developed for determination of ('15)N-labeled N(,2), and (ii) to use these procedures to study the evolution of N(,2) and N(,2)O from ('15)N-fertilized soil cores subjected to wetting and drying cycles.
The procedure developed for determination of ('15)N-labeled N(,2)O involves dilution of this N(,2)O with a known amount of unenriched N(,2), reduction of the N(,2)O to N(,2) in a heated tube containing reduced copper, and determination of r and r' with a dual-inlet ratio mass spectrometer. This procedure is accurate and precise; it permits measurement of ('15)N-labeled N(,2)O without interference by CO(,2); it allows calculation of the average ('15)N enrichment of the N pool from which this N(,2)O was derived; and it permits N(,2)O analysis of an atmospheric sample previously analyzed for ('15)N-labeled N(,2).
Studies of N(,2) and N(,2)O evolution from intact soil cores treated with ('15)N-labeled KNO(,3) or (NH(,4))(,2)SO(,4) and periodically treated with water to simulate rainfall indicated that N(,2) and N(,2)O evolved from soils originate largely through denitrification of NO(,3)('-) under anaerobic conditions and that evolution of these gases follows an overall cycle associated with the wetting and drying of the soil. Very little, if any, N(,2) and N(,2)O was evolved when the soil moisture content was well below field capacity. Evolution virtually ceased when the soil was saturated with water, and it subsequently increased as the soil dried, with more N(,2) usually being evolved than N(,2)O. Maximal evolution occurred 2 to 9 days after the water had been applied, and evolution then decreased and eventually ceased.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.
|Date Available in IDEALS:||2014-12-16|