Does the use of different nitrogen fertilizers reduce greenhouse gas emissions in corn-ryegrass succession in floodplain soils?

Floodplain soils are being cultivated with rainfed crops such as corn ( Zea mays L.) and ryegrass ( Lolium multiflorum L.). Although the cultivation of these crops reduces methane (CH 4 ) emissions, the use of nitrogen fertilizers associated with the particular conditions of these soils may be contributing to higher nitrous oxide (N 2 O) emissions. Therefore, this study aimed to evaluate greenhouse gas (GHG) emissions and global warming potential associated with different N sources in a corn–ryegrass succession cultivated under rainfed conditions in floodplain soil with low organic matter content. The field experiment was conducted over three growing seasons in Planosol, under the corn-ryegrass succession. The treatments consisted of control (no N), common urea, calcium ammonium nitrate (CAN), and urea+NBPT, with rates of 160 and 80 kg N ha −1 , respectively, used for corn and ryegrass, both applied to broadcast. The accumulated fluxes and emissions of N 2 O and CH 4 , the soil parameters attributed to the emissions, the partial global warming potential (pGWP), yield-scaled GHG emission (YpGWP), emission factor (EF), grain/biomass yield of crops and N use efficiency (NUE) were evaluated. The CAN presented high N 2 O emissions, 38.5% higher than the other treatments. CAN presented average pGWP values ​​​​​​around 67.8% higher than urea and urea+NBPT. In 2024 ryegrass, urea+NBPT presented the lowest pGWP, being similar to the control. The EF presented 66% of values above the IPCC estimate of 1.6% of applied N. Although all N sources increased N 2 O emissions relative to the control, urea and urea+NBPT resulted in lower YpGWP than CAN in floodplain soils. • Calcium ammonium nitrate (CAN) increased N₂O emissions by 38.5% compared to other N sources. • Urea and urea+NBPT reduced yield-scaled GHG emission (YpGWP) by 40.5% compared to CAN. • Emission factors exceeded the IPCC standard (1.6%) in 66% of cases.