“…During the past few years, laboratory studies have contributed signifi cantly to our understanding of the mechanisms by which N2O is produced in soils and have indicated that N2O is produced in soils by several mechanisms. Production of N2O has been found to occur during dissimilatory nitrate reduction by non-denitrifying soil microorganisms (Smith and Zimmerman, 1981;Smith, 1982), during chemodenitrification of ni trite in soil Smith and Chalk, 1980a;Christianson and Cho, 1983;Ghoshal, 1983), and during oxidation of ammonium by soil microorganisms (Yoshida and Alexander, 1970;Ritchie and Nicholas,1972;Blackmer,1978,1980;Blackmer et al, 1980;Goreau et al, 1980;Smith and Chalk, 1980b;Lipschultz et al, 1981).…”