N₂O and CO₂ emissions following clover and cellulose incorporation into a New Zealand pastoral soil

Abstract

Clover (Trifolium repens L.) and clover + different proportions of cellulose were incorporated into soil and the nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions measured. Ground, dried clover shoots and cellulose were mixed to carbon: nitrogen (C: N) ratios of ~9 (‘clover only’), 20, 30 and 40. Soil samples were incubated at water–filled pore space (WFPS) of 86% and 20°C. Over 42 d, N₂O emissions from the controls averaged 9 mg/kg soil (6 g total N/kg soil), indistinguishable from the ‘clover only’ (1.5 g N incorporated/kg soil) and ‘C: N 20’ treatments. Corresponding N₂O emissions from the ‘C: N 30’ and ‘C: N 40’ treatments averaged nearly 50% greater (P <0.05) and these two treatment effects were indistinguishable. Over 42 d, CO₂ emissions from the controls averaged 4 g/kg soil. There was a linear C (incorporation rate) ‘dose effect’ on CO₂ emissions (0.15 g CO₂/g C, R² = 0.80) with no difference between clover and clover + cellulose. Over 145 d, CO₂ emissions from the controls averaged 17 g/kg soil and the C ‘dose effect’ was 0.38 g CO₂/g C (R² = 0.98). Incorporating different plant materials into soil affected the N₂O and CO₂ emissions differently.