Nitrous oxide emissions from a grass seed crop rotation with tall fescue (Festuca arundinacea L.) on sandy loam soil

Nitrous oxide (N 2 O) emissions may contribute significantly to the carbon footprint of grass seed production systems. However, N 2 O emissions depend on soil conditions and climate, and therefore region-specific documentation is needed. This study quantified N₂O emissions from an experimental crop rotation with first-year (GS1) and second-year (GS2) tall fescue ( Festuca arundinacea L. ), sugar beet (SuB), and spring barley undersown with the grass seed crop (SBus). Nitrous oxide emissions from fertilised and unfertilised field plots were measured with static chambers during spring 2022, and between autumn 2022 and early spring 2024. Without disturbance of the surrounding soil, diffusion probes were installed to 5, 10, 20 and 50 cm depth in all treatments to investigate sources of N 2 O, and soil was sampled to monitor soil mineral N dynamics. Cumulative N₂O emissions varied among rotation stages and years. Fertilised SuB produced higher annual emissions (3.8 kg N₂O-N ha⁻¹) than the other crops, although in part this was derived from residues of the previous crop (GS2). Nitrous oxide emission factors (EFs) for N fertilisers in spring 2022 ranged from 0.12% (GS2) to 0.84% (SuB), while in the 2023 growing season the annual EFs varied from −0.12% (SBus) to 1.16% (SuB), and the average annual N 2 O EF for the crop rotation was 0.46%. Yield-scaled N 2 O emissions were similar between crops with respect to emissions during spring, but annually grass seed crops had higher yield-scaled N 2 O emissions reflecting the higher N input across the year. Soil N 2 O concentration profiles varied between crops and seasons, with higher concentrations near the soil surface after fertilisation in spring, while in other periods, N 2 O accumulation at depth in the soil indicated residue decomposition. In both years the spring period, where most of the N fertiliser was applied, was dominated by a negative water balance, and this may explain why the N 2 O emission level was comparable to that expected for a dry climate.