Soil CO2 emissions during the winter–summer crop rotation fallow period: Influence of tillage, nitrogen fertilization, and weed growth in a long-term field trial

Abstract

Soil respiration is a key component of the carbon cycle, yet it remains understudied during fallow periods, particularly in Mediterranean cropping systems where fallows can exceed nine months. As the carbon credit market emerges, accurately quantifying CO₂ emissions year-round has become increasingly important. This study assessed soil respiration and its abiotic and biotic drivers, such as soil temperature and water content, weed biomass and composition, under two different tillage management, long-term conventional tillage (CT) and no-tillage (NT), combined with two nitrogen levels (0 and 180 kg N ha⁻¹ yr⁻¹). Monitoring was conducted during two fallow periods (2022–2023 and 2023–2024) between durum wheat harvest and maize sowing. Soil temperature and water content followed typical Mediterranean trends, with summer heat peaks and higher winter moisture; NT plots had significantly higher average temperatures and winter soil moisture than CT, regardless of fertilization. Soil CO₂ emissions were low and similar across treatments in winter but diverged in warmer seasons. In 2022–23, NT showed significantly higher emissions than CT (up to +65 %), while in 2023–24, only NT0 exceeded CT180 (+48 %). Emissions were positively correlated, although weakly, with temperature and negatively with moisture, especially under NT. Soil cover, dominated by Poaceae, fluctuated seasonally and was consistently greater in NT, with notable differences in species composition. These results emphasize the relevance of fallow-period emissions in carbon budgeting and the potential role of spontaneous vegetation in carbon dynamics. Incorporating such insights into carbon farming frameworks will be essential for improving the accuracy and integrity of climate-related agricultural policies.