Long-term effect of no-tillage on soil CO2 emissions during the fallow period between winter and summer crops

Soil CO₂ emissions are a critical component of the carbon cycle, serving as a key indicator of soil fertility and health. Tillage practices significantly influence soil organic matter accumulation, making the monitoring of soil CO₂ emissions crucial in the context of Carbon Farming. The Mediterranean region, identified as a climate change hotspot, faces alterations in rainfall and temperature patterns that not only affect crop yields but also impact the soil carbon cycle. In Mediterranean agriculture, a common practice is the rotation of winter (e.g., durum wheat) and summer (e.g., maize) crops, typically involving a nine-month fallow period between the harvest of the winter crop (around July) and the sowing of the summer crop (around April). Despite its importance, this fallow period remains underexplored in studies of soil CO₂ emissions.

This study quantifies soil CO₂ emissions, temperature, and moisture during the fallow period in a Mediterranean winter-summer rotation system, examining the effects of long-term tillage intensity. The research was conducted on a long-term experimental trial established in 1994 in Agugliano, Central Italy. The site features silty-clay soil (pH 8.3) with an average annual rainfall of 820 mm and a mean temperature of 15.3 °C. The long-term trial involves a split-plot design that includes three tillage levels (conventional tillage at 0–40 cm, reduced tillage at 0–10 cm, and no-tillage) and three nitrogen levels (0, 90, and 180 kg N/ha/year). This study focuses on conventional tillage (CT) and no tillage (NT) with no nitrogen fertilization to isolate tillage effects. Soil CO2 emissions were measured biweekly from July 2022 to March 2023 using a portable infrared gas analyser. Concurrently, soil temperature and moisture at 0–10 cm depth were recorded.

Results revealed that soil CO₂ emissions in NT closely followed precipitation patterns during summer, showing distinct CO₂ pulses, while emissions in winter were negligible due to low temperatures despite higher soil moisture. In spring, rising temperatures led to significantly higher emissions in NT compared to CT. Positive correlations between CO₂ emissions and soil temperature, and negative correlations with soil moisture, were observed. Cumulative CO₂ emissions during the fallow period were 0.35 and 0.55 t/ha for CT and NT, respectively.

These findings highlight the importance of extending soil CO₂ monitoring beyond the crop-growing season to the fallow period, especially in no-tillage systems. These practices are crucial for accurate carbon accounting and assigning credits in carbon markets.