THE EFFECT OF FLOODING ON NITROUS OXIDE EMISSIONS FROM AN ORGANIC SOIL

Abstract

To determine the effect of flooding of Pahokee muck (a drained, cultivated Histosol) on nitrous oxide emissions from the soil, we measured field N2O fluxes and N2O produced in soil samples incubated under controlled laboratory conditions. During the first 5 days of flooding of a field that had previously been cropped to sweet corn (Zea mays L. rugosa), the NO3--N levels declined from 68 to <0.1 microgram nitrogen per cubic centimeter. Similarly, the N2O flux decreased from 174 g N/ha/d prior to flooding to approximately 0 after flooding. Comparing the flux values and the N2O concentrations in the flood water suggested that the flooded field may have acted as a sink for atmospheric N2O. In laboratory-incubated samples of the preflood and flooded soils, the potential denitrification rates increased from 16.2 μg N/cm3/day prior to flooding to 31.2 μg N/cm3/d after flooding. Whereas N2O was the major product of denitrification in soil samples collected prior to flooding, very little N2O accumulated in samples collected from the flooded field. Nitrous oxide was readily reduced in the flooded soil in the presence of NO3--N and NO2--N concentrations of 100 and 3 mg/liter, respectively.