CO₂ And N₂O Emission Characteristics And Impact Factors Infarmland Under Biogas Slurry Irrigation

In China,more biogas slurry from the anaerobic digestion of livestock breeding wastewater has been applied to soil irrigation. It is beneficial for the recycling of livestock breeding wastewater. however, inappropriate irrigation caused many environmental problems. Recently, there are many reports on the effect of biogas slurry irrigation on soil, crops and groundwater quality. However, less reports has been found in greenhouse gas emissions using biogas slurry as fertilizer and irrigation water. Thus, the objectives of this field experiment were to investigate the impact of biogas slurry irrigation on CO2 and N2 O emissions in corn-wheat rotation system, to monitor the soil characteristics and to determine the crop yields. Specifically, soil moisture, soil NO3--N, soil NH4 +-N, soil dissolved organic carbon in the 0~5 cm soil and crop yields were analyzed in the growth period of winter wheat and summer maize. The emission fluxes of greenhouse gas from soil after biogas slurry irrigation in winter wheat-summer corn rotation system were discussed.1) The daily and weekly characteristics of CO2 and N2 O emissions after biogas slurry irrigation were investigated. The CO2 and N2 O emissions were increased significantly after biogas slurry irrigation. Daily CO2 and N2 O fluxes were consistent with the daily temperature variation, which were low at night and high during the day. The average fluxes were closed to the emissions of 08:00-11:00 am, which were the most representative sampling time. Significant positive correlations(P <0.05) among gas emissions, temperature of 5cm soil and temperature of surface soil were observed in the first 24 hours after irrigation. The result also proved that there was no significant difference among three treatments on the 7th days after irrigation, which indicated that the first week was the most important monitoring period after the application of biogas slurry on the soil.2) The variation trends of CO2 and N2 O emissions in soil of winter wheat and summer maize rotation system were dertermined after biogas slurry irrigation. During the whole monitoring period, the variations of CO2 and N2 O fluxes were not changed. Among all the treatments, four emission peaks of CO2 were observed separately in the wintering stage, returning green stage, elongation stage and grouting stage of wheat season, which were important growth periods to the wheat. And three peaks of CO2 were observed during maize season. All the factors including the differences of irrigation, fertilization, temperature and vigorous root activitie could result in the CO2 and N2 O emission peaks. The N2 O emissions peak appeared immediately after the biogas slurry irrigation, and dropped to the average level in short time. Compared with conventional fertilization, irrigation with 2:1 biogas slurry did not increase the accumulation of CO2 and N2 O emissions. In addition, the treatment showed the same crop yield with the traditional fertilization, when the irrigation ratio of biogas slurry and water was 2:1. It was significantly higher than the treatment of contrast. The soil NO3--N, NH4 +-N and soil DOC were increased after biogas slurry irrigation in short term, which indicated that N2 O emission fluxes were mainly determined by the soil DOC, NO3--N and WFPS, while CO2 emission fluxes were mainly affected by soil DOC.In conclusion, the CO2 and N2 O emissions of virous treatments irrigated with 2:1 biogas slurry from livestock breeding wastewater were not increased, Where the optimal irrigation irrigated with 2:1 biogas slurry three times guaranteed yield, model guaranteed the crop yield with twice irrigations in wheat season(winter period, turning green) and once in season maize season(corn planting), when the volume ratio of biogas slurry and water was 2:1,which is a reasonable mode. In this study, the peaks of CO2 and N2 O emissions appeared in a week after fertilization, irrigation and, rainfall. Thus, more sampling frequency was suggested to conduct in the first 7 days after fertilization, irrigation and rainfall, otherwise less sampling in other time.The results from this study provided theoretical basis for assessing the effects of biogas slurry irrigation on CO2 and N2 O emissions, and exploring the contribution of breeding/planting coupling process to greenhouse gas emissions. Especially, it can provide the scientific foundation for the government to make policies on greenhouse gas reduction and carbon and nitrogen management in soil.