Denitrification, organic matter and redox potential transformations in Cambisols

Twogreenhouse gases: N2O and CO2 as well as Corg and redox potential transformation were investigated. Four- teen Cambisols (0-10 cm) developed from sand, silt, loess, loam and clay characteristic for Poland were incubated under flood conditions in closed flasks at 20°C temperature for 7 days. Ac- cording to denitrification activity the soils were divided into two groups - of lower (I) and higher (II) activity. Production of nitrous oxide lasting 3-5 days was followed by its absorption in the case of three soils out of fourteen. The total N2O amount reached from 3-91% of the initial nitrate - N content and was positively cor- related with the Corg content. Diurnal N2O production was posi- tively correlated with Corg and diurnal CO2 emission. The N2O ab- sorption rate for the three soils was 0.16 mg N2O-N kg -1 day -1 , 20.6 mg N2O-N kg -1 day -1 and 3.3 mg N2O-N kg -1 day -1 in sandy, loamy and in the clay soil, respectively. The diurnal fluxes of carbon dioxide ranged from 1.24 to 9.96 mg of CO2-C kg -1 d -1 and from 26.8 to 144 mg of CO2-C kg -1 for I and II group, respectively. Diurnal carbon dioxide production showed a high positive cor- relation with Corg. The soils investigated were characterised by a very wide range of redox potential measured for the maximal cu- mulative N2O emission from +417 to +233 mV. The beginning of N2O emission from the light textured soils was observed above 400 mV while from the heavier textured soil below 400 mV. N2O emis- sion was correlated with soil redox potential. Keywords : N 2O emission, N2O absorption, redox po- tential, soil respiration, CO2:N2O ratio