Nitrous oxide emissions in nonflooding period from fallow paddy fields

The study was conducted to investigate the N2O emissions and dissolved N2O in the leachate during the nonflooding period in nongrowing paddy fields. Three kinds of paddy soils were repacked to soil columns and were supersaturated with water initially and dried gradually in a greenhouse to attain the N2O emissions flux during the incubation. Soils with the texture of silty clay-loam (Q and H) produced cracks during the drying of soil, but soil with the texture of silty loam (X) did not form the cracks. Cracked soils had similar amount of N2O emissions, and the mean N2O flux was 1,280.9 and 1,133.3 μg/(m2·h) from Q and H soil, respectively, during the incubation; whereas the mean N2O flux from noncracked X soil was 426.3 μg/(m2·h), i.e., significantly different from cracked soils. From cracked soils, the diurnal N2O emissions reached two peaks at 14:00 and 2:00, but such emissions peaked only at 2:00 from noncracked soil. The dissolved N2O concentrations in leachates from noncracked soil columns were greater than those from the cracked soil columns, and it indicated that the preferential flow might not affect the amounts of dissolved N2O in leachates during soil cracking. Supersaturated dissolved N2O in the leachate was potential source of N2O emissions. Fallow paddy fields have big risks of N2O emissions during nonflooding periods.