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.