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.

Key Words:

• carbon dioxide
• direct emission
• indirect emission
• methane
• nitrous oxide