Effect of soil water content on denitrification during cover crop decomposition

Experiments were conducted to assess the effects of soil water content on d enitrification during hairy vetch (Vicia Villosa) decomposition. Hairy vetc h plants were grown from seed to maturity in soil cores. Before and after k ill, simulated rainfall was applied to cores weekly and leachate was analyz ed for NO3- and NH4+. Denitrification incubations (ca. 48 h duration) were conducted 3, 17, 31, and 45 days after kill using the acetylene block metho d. Soil water content was varied systematically to give a range of percent water-filled pore space (WFPS) values from field capacity (60%) to saturati on (100%), Little denitrification occurred on Day 3 (<2 mg N2O-N), Substant ial denitrification occurred on Days 1.7, 31, and 45, with maxima of 44, 27 , and 30 mg N2O-N produced in saturated cores, respectively, accounting for approximately 60 to 75% of the total inorganic N (NO3- + NH4+ N2O) present in cores. There was an apparent linear relationship between denitrificatio n and soil water content (WFPS), with a threshold for denitrification at ca . 60% WFPS, Cumulative N lost from cores during four denitrification incuba tions ranged from 1 to 48 Kg N ha(-1), depending on percent WFPS, Rates of N mineralization were relatively linear after denitrification incubations ( 55 days). Cumulative N mineralized from unsaturated cores was ca, 190 Kg N ha-L through 120 days after kill, These data indicate that substantial quan tities of vetch-N may be lost during decomposition.