Prediction of future carbon footprint and ecosystem service value of carbon sequestration response to nitrogen fertilizer rates in rice production

There is concern for variations of the carbon footprint (CF) and ecosystem service value of carbon sequestration (ESVCS) related to nitrogen (N) fertilizer rate in rice production under future climate change. To explore possible future ecological effects of N fertilizer rate, a DeNitrificationDeComposition (DNDC) model combined with Representative Concentration Pathway (RCP) projections (RCP 4.5 and RCP 8.5) were used to predict the CF and ESVCS of rice production. The model was validated by a two-year field experiment, and then seven N fertilizer levels (0, 75, 150, 190, 225, 300, and 375 kg N/ha) were set for prediction from 2015 to 2050. The validation results indicated a good fit between the DNDC-simulated and observed data of GHG emission and rice yield. Under RCP 8.5, the mean CF was 4.58.7% higher and the average ESVCS was 3.67.4% lower than those under RCP 4.5. The effects of N fertilizer rate on CF and ESVCS were consistent between the two climate change scenarios. In both RCPs, it was found that CF and ESVCS were mainly influenced by N fertilizer rate due to the latter's effect on CH4 emissions and crop carbon fixation. CH4 was the main contributor to CF during 20152050, accounting for 43.958.3% of the total CF. Agricultural inputs were also large contributors to CF, and N fertilizer increased the indirect GHG emissions by 24.6122.2% compared with no N fertilization treatment. Among the studied N fertilizer rates, 190 kg N/ha was the optimal rate, obtaining the lowest CF and highest ESVCS. These results indicate that, under future climate change, an N fertilizer rate of 190 kg N/ha could achieve a trade-off between high yield, reduction of CF, and improvement of ESVCS in rice production.