Evaluating N₂O emissions and carbon sequestration in temperate croplands with cover crops: insights from field trials

<p>Cover crops (CCs) are acclaimed for enhancing the environmental sustainability of agricultural practices by aiding in carbon (C) sequestration and reducing losses of soil mineral nitrogen (SMN) after harvest. Yet, their influence on nitrous oxide (<span class="inline-formula">N₂O</span>) emissions – a potent greenhouse gas – presents a complex challenge, with findings varying across different studies. This research aimed to elucidate the effects of various winter CCs – winter rye (frost-tolerant grass), saia oat (frost-sensitive grass), and spring vetch (frost-sensitive legume) – compared to a bare fallow control on SMN dynamics, <span class="inline-formula">N₂O</span> emissions, and C sequestration. These effects were determined by measuring SMN dynamics and <span class="inline-formula">N₂O</span> emissions in field experiments. The effects of CCs on soil C sequestration over a 50-year period were predicted by soil organic C (SOC) models using measured aboveground and belowground CC biomass. While CCs efficiently lowered SMN levels during their growth, they slightly increased <span class="inline-formula">N₂O</span> emissions compared to bare fallow. In particular, winter frost events triggered significant emissions from the frost-sensitive varieties. Moreover, residue incorporation and tillage practices were associated with increased <span class="inline-formula">N₂O</span> emissions in all CC treatments. Winter rye, characterized by its high biomass production and nitrogen (N) uptake, was associated with the highest cumulative <span class="inline-formula">N₂O</span> emissions, highlighting the influence of biomass management and tillage practices on N cycling and <span class="inline-formula">N₂O</span> emissions. The CC treatment resulted in a slight increase in direct <span class="inline-formula">N₂O</span> emissions (<span class="inline-formula">4.5±3.0</span>, <span class="inline-formula">2.7±1.4</span>, and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">3.1</mn><mo>±</mo><mn mathvariant="normal">3.8</mn><mspace width="0.125em" linebreak="nobreak"/><mrow class="unit"><mi mathvariant="normal">kg</mi><mspace linebreak="nobreak" width="0.125em"/><msub><mi mathvariant="normal">N</mi><mn mathvariant="normal">2</mn></msub><mi mathvariant="normal">O</mi><mo>-</mo><mi mathvariant="normal">N</mi><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">ha</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="122pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="e65564e6ffe09ed8f8f419c46bd84065"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-11-489-2025-ie00001.svg" width="122pt" height="16pt" src="soil-11-489-2025-ie00001.png"/></svg:svg></span></span> for rye, oat, and vetch, respectively) compared to the fallow (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">2.6</mn><mo>±</mo><mn mathvariant="normal">1.7</mn><mspace linebreak="nobreak" width="0.125em"/><mrow class="unit"><mi mathvariant="normal">kg</mi><mspace width="0.125em" linebreak="nobreak"/><msub><mi mathvariant="normal">N</mi><mn mathvariant="normal">2</mn></msub><mi mathvariant="normal">O</mi><mo>-</mo><mi mathvariant="normal">N</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">ha</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="122pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="148d1da385bc02e394c04dd3d4223c24"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-11-489-2025-ie00002.svg" width="122pt" height="16pt" src="soil-11-489-2025-ie00002.png"/></svg:svg></span></span>) over the entire trial period (18 months). However, the potential of non-legume CCs to reduce indirect <span class="inline-formula">N₂O</span> emissions compared to fallow (<span class="inline-formula">0.3±0.4</span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.2</mn><mo>±</mo><mn mathvariant="normal">0.1</mn><mspace linebreak="nobreak" width="0.125em"/><mrow class="unit"><mi mathvariant="normal">kg</mi><mspace linebreak="nobreak" width="0.125em"/><msub><mi mathvariant="normal">N</mi><mn mathvariant="normal">2</mn></msub><mi mathvariant="normal">O</mi><mo>-</mo><mi mathvariant="normal">N</mi><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">ha</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">a</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="140pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="72e7097d5182e0b560823bdc8d1956b5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-11-489-2025-ie00003.svg" width="140pt" height="16pt" src="soil-11-489-2025-ie00003.png"/></svg:svg></span></span> for rye and oat, respectively) and their contribution to C sequestration (120–150 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M18" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">kg</mi><mspace width="0.125em" linebreak="nobreak"/><mi mathvariant="normal">C</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">ha</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">a</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="65pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="0d5dee1caffb7a62d26638443b1b7069"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-11-489-2025-ie00004.svg" width="65pt" height="15pt" src="soil-11-489-2025-ie00004.png"/></svg:svg></span></span> over a period of 50 years when CCs were grown every fourth year) might partially counterbalance these emissions. Thus, while CCs provide environmental benefits, their net impact on <span class="inline-formula">N₂O</span> emissions requires further research into optimized CC selection and management strategies tailored to specific site conditions to fully exploit their environmental advantages.</p>