Abstract: Studies of the activities of soil nitrate reductase, nitrite reductase and hydroxylamine reductase in maize growing season and their relationship with soil water content, NO₃^--N content and N₂O emission under fertilization showed that these three denitrifying enzymes had a significant seasonal variation and were influenced by soil water content and fertilization. The relationship between soil denitrifying enzymes, soil water content and N₂O emission were further investigated, which indicated that the activities of soil denitrifying emzymes could be an index to distinguish the ways of N₂O Oproductions in upland field.

Key words: Denitrifying enzymes, NO₃^--N, Soil water content, N₂O