N2O emissions from controlled-release and conventional N-fertilizers applied to red-yellow soil in Okinawa, Japan

In Okinawa, Japan, controlled-release N fertilizers (CRFs) are promoted to reduce labor and to increase fertilizer use efficiency. However, N 2 O emissions from N fertilizer applied to the widely prevalent Kunigami mahji (red-yellow soil), a local soil in the region, have not been examined so far. We conducted two laboratory experiments during winter and spring to compare N 2 O emissions between CRF and standard fertilizer (ammonium sulfate: AS) in kunigami mahji . Two seasons were selected to explore the effects of moisture and temperature on N 2 O emissions in relation to N fertilization. For each experiment, three soil chambers were used, each containing 1.4 kg of soil: one served as a control, and the other two received 1 g of nitrogen from either a linear-release-type CRF with 42 % N or AS with 21 % N. Over 9 weeks, N₂O emissions from the headspace of each chamber were measured every minute for 20 min, followed by 70 min of ventilation, in a continuous 90-minute cycle repeated throughout the study. Soil moisture, soil temperature, NO, and NO 3 -N and NH 4 -N in leachate were also analyzed. In Exp A (winter), nitrification was dominant, and N 2 O emission from CRF (emission factor, EF, 0.4 %) was 88 % lower than that from AS (EF 3.9 %). In Exp B (spring), denitrification was dominant, and N 2 O emission from CRF (EF 1.9 %) was 53 % lower than that from AS (EF 4 %). The frequently lower water-filled pore space (WFPS) in Exp A than in Exp B facilitated higher NO emission from AS than from CRF. Due to the consistently high WFPS in Exp B, most of the NO 3 − in the soil was reduced to N 2 O and N 2 . N is more readily available in AS than in CRF, facilitating higher cumulative leaching of NH 4 -N from AS. However, in both experiments, AS was denitrified more than CRF, producing more N 2 O and resulting in lower leaching of NO 3 -N. Our results highlight that choosing the appropriate form of fertilizer and good management of soil moisture content can reduce N 2 O emissions and leaching of NO 3 − and NH 4 + . • Controlled-release N fertilizer emits low N 2 O and NO in red-yellow soil. • Irrigation events regulate N₂O production by influencing nitrification and denitrification. • Ammonium sulphate was more denitrified than controlled-release N fertilizer.