Effect of crop residue C:N ratio on N₂O emissions from Gray Lowland soil in Mikasa, Hokkaido, Japan

Abstract

We studied the effect of crop residues with various C:N ratios on N₂O emissions from soil. We set up five experimental plots with four types of crop residues, onion leaf (OL), soybean stem and leaf (SSL), rice straw (RS) and wheat straw (WS), and no residue (NR) on Gray Lowland soil in Mikasa, Hokkaido, Japan. The C:N ratios of these crop residues were 11.6, 14.5, 62.3, and 110, respectively. Based on the results of a questionnaire survey of farmer practices, we determined appropriate application rates: 108, 168, 110, 141 and 0 g C m⁻² and 9.3, 11.6, 1.76, 1.28 and 0 g N m⁻², respectively. We measured N₂O, CO₂ and NO fluxes using a closed chamber method. At the same time, we measured soil temperature at a depth of 5 cm, water-filled pore space (WFPS), and the concentrations of soil NH⁺ ₄-N, NO⁻ ₃-N and water-soluble organic carbon (WSOC). Significant peaks of N₂O and CO₂ emissions came from OL and SSL just after application, but there were no emissions from RS, WS or NR. There was a significant relationship between N₂O and CO₂ emissions in each treatment except WS, and correlations between CO₂ flux and temperature in RS, soil NH⁺ ₄-N and N₂O flux in SSL and NR, soil NH⁺ ₄-N and CO₂ flux in SSL, and WSOC and CO₂ flux in WS. The ratio of N₂O-N/NO-N increased to approximately 100 in OL and SSL as N₂O emissions increased. Cumulative N₂O and CO₂ emissions increased as the C:N ratio decreased, but not significantly. The ratio of N₂O emission to applied N ranged from −0.43% to 0.86%, and was significantly correlated with C:N ratio (y = −0.59 ln [x] + 2.30, r ² = 0.99, P < 0.01). The ratio of CO₂ emissions to applied C ranged from −5.8% to 45% and was also correlated with C:N ratio, but not significantly (r ² = 0.78, P = 0.11).

Key words:

• C:N ratio
• emission fraction
• N₂O
• residue
• soil

ACKNOWLEDGMENTS

This work was financially supported by the Global Environmental Research Program of the Ministry of the Environment of Japan (No. S-2). The authors thank Akane Kagemoto and Yuu Hirose for help with collecting data, and Takeshi Morimoto for permission to use their onion fields.