Nitrous oxide emissions and emission factors in hairy vetch-maize sequences: The role of vetch termination timing on nitrogen synchronization

Abstract

Nitrous oxide (N₂O) emissions from agricultural soils represent a major environmental concern and require sustainable nitrogen (N) management strategies. The timing of hairy vetch (Vicia villosa Roth) termination was investigated to improve N synchronization and to assess its potential to replace fallow as an alternative N source for maize (Zea mays L.) without increasing N2O emissions compared to urea, while maintaining productivity. An experiment was conducted over two seasons to assess N2O emissions (43 measurements per season) and soil N dynamics in fallow/maize and vetch/maize sequences with two termination timings. Cumulative N₂O emissions in vetch/maize sequence ranged from 0.59 to 1.77 kg N₂O-N ha⁻¹ , while in fallow/maize ranged from 0.55 to 1.18 kg N₂O-N ha⁻¹ . Nitrogen fertilization increased emissions by 4.5–17.6 %, while the use of vetch before maize increased them by 9.6–48.5 % compared to fallow/maize sequence. Reducing the interval between vetch termination and maize sowing from ~31 days (early termination) to ~10 days (late termination) improved N synchronization by 13 %. Late vetch termination and N-fertilized fallow showed similar N₂O emissions, with improved synchronization reducing emissions by 13–21 % compared to early termination. Regression trees identified soil temperature, ammonium, and water-filled pore space (WFPS) as key drivers of N₂O emissions during the fallow or vetch period, whereas nitrate and WFPS became the dominant factors during the maize season. Furthermore, the first emission factors for hairy vetch (< 0.17 %) were reported, which were significantly lower than the IPCC default (1 %). These findings offer critical insights into refining greenhouse gas inventories and optimizing vetch management to reduce emissions while maintaining or enhancing maize productivity.