Dissolved N2O, CH4, and CO2 emissions from subsurface-drainage in a structured clay soil cultivated with onion in Central Hokkaido, Japan

Abstract

In the soil system, the greenhouse gases (N2O, CH4 , and CO2 ) are produced by microbes or root respiration. These gases diffuse into the atmosphere directly. At the same time, they leach into ground water after their dissolution into drainage water. The dissolved gases are secondarily emitted after drainage water is discharged to the ground surface. From April 2000 to March 2001, we measured these greenhouse gas emissions through subsurfacedrainage in a gray lowland soil in central Hokkaido, Japan. Direct emissions of N2O, CH4, and CO2 from the soil surface were also measured. The concentration of each gas was several orders higher than the concentration equilibrated with ambient air. The CH4 concentration ranged from 1.0 to 113 µg CH4-C L−1 and was lower in the growing season (May–October) due to oxidative soil conditions. The N2O concentration ranged from 19.3 to 189 µg N2O-N L−1 and was higher in the growing season. The increase in the N2O concentration was probably due to an increase in the denitrification process in the soil profile. There was no significant relationship between the concentration of dissolved N2O and the NO3 concentration. The CO2 concentration ranged from 15.5 to 30.7 µg CO2-C L−1 and was higher in the snow season (November–March). Relatively higher indirect emissions of all the gases (dissolved concentration × flow rate of the subsurface-drainage) were observed in the snowmelt season (April) and after heavy rain. The annual indirect emissions through the subsurface-drainage were calculated to be 0.747 kg N2O-N ha−1 , 0.115 kg CH4-C ha−1, 132 kg CO2-C ha−1, which corresponded to 4.6, 58, and 2.5% of direct emissions, respectively.