Nitrous oxide and carbon dioxide emission responses to litter incorporated in a grassland soil

Abstract

While the Intergovernmental Panel on Climate Change (IPCC) guidelines include the possibility of N₂O emissions from crop residues, they do not include grazed pasture or supplementary feed litters. To quantify the relative greenhouse gas (GHG) emissions from pasture litter, ground shoots of clover (Trifolium repens L.), ryegrass (Lolium perenne L.) and maize (Zea mays L.) were incorporated into soil at 1.5, 1.0 and 0.6 g nitrogen (N) (~12.8 g carbon (C), on average) kg⁻¹ soil, respectively. A 42 d incubation at 20°C and either 86% (field capacity) or 54% water-filled pore space (WFPS) was performed. During the first 2 d, 92–95% of the N₂O was emitted. At 86% WFPS, N₂O emissions were 2–3% of the incorporated N with no litter species differences. At 54% WFPS, N₂O emissions were 1.7% > 0.7% = 0.5% of herbage N applied, for clover, ryegrass and maize, respectively (P <0.001). At 86% and 54% WFPS, carbon dioxide (CO₂) emissions averaged 32% and 21%, respectively, with no litter species differences after 38 d. Over 14 d, N₂O emissions expressed as CO₂–eq were 67 and 59% for clover, 59 and 31% for ryegrass and 52 and 18% for maize at 86% and 54% WFPS, respectively, of the total (CO₂+N₂O) greenhouse gas budget. Emissions of N₂O corresponded with the biochemical composition of the litter. At either WFPS, the decomposition rates did not differ due to species. The potential for pasture litter to contribute to N₂O emissions from clover-ryegrass pastures warrants further study in situ.