Emission Characteristics Of Greenhouse Gases From Winter Wheat-Summer Maize Rotation Under Biogas Slurry Irrigation

With the rapid development of intensive and large-scale livestock breeding industry,the scale of irrigating farmlands by biogas slurry is growing.While achieving sewage waste resource utilization,unreasonable irrigation has brought serious environmental problems.A large number of studies have been carried out on biogas slurry irrigated farmland,but mostly focused on the study of soil,groundwater and crop,there are less studies on soil greenhouse gas emissions,especially it is short of biogas slurry quantitative irrigation about farmland greenhouse gas emission.In this experiment,six different biogas slurry irrigation models were set up,that was,blank control treatment CK,conventional fertilization treatment CF,irrigated twice 2:1 biogas slurry treatment(T1),irrigated three times 2:1 biogas slurry treatment(T2),irrigated four times 2:1 biogas slurry treatment(T3),irrigated five times 2:1 biogas slurry treatment(T4),positioning field test and static box-gas chromatography methods are used,to reaserch the emission characteristics of main greenhouse gases CO2,N2O and CH4 after irrigation which dairy farm biogas slurry replacing the total fertilize,in the North China Plain under the typical winter wheat-summer maize rotation system.Simultaneously,the dynamic changes of weather conditions(precipitation and atmospheric temperature),soil physical and chemical properties(soil ammonium nitrogen,nitrate nitrogen and soluble organic carbon),soil urease activity and crop grain yield were monitored,and the emission flux of CO2,N2O,CH4 and the correlation of each soil factor were analyzed.The most reasonable biogas slurry irrigation model was put forward,by weighing crop yield,greenhouse gas emissions and soil factors.The following test results were got:1.The seasonal emission law of soil CO2 was not changed by biogas slurry irrigation,the emission flux of CO2 in the field was 1.39-23.82 kg CO2-C ha-1·d-1;The CO2-C cumulative emissions of CK,T1,T2,T3,T4 and CF were 1985.13,2424.55,2576.42,2759.88,2893.79,2797.65 kg-ha-1,the order was T4>CF>T3>T2>T1>CK,there was no significant difference in CO2-C accumulation between the treatments of soil biogas slurry and chemical fertilizers.2.N2O emission flux maximum appeared after biogas slurry irrigation in T2,T3,T4,and the difference with conventional fertilization treatment(CF)reached a significant level;In addition to T4 and conventional fertilization treatment(CF),in the winter other treatments showed N2O negative emissions phenomenon;T3 and T4 treatments did not result in a significant increase in soil N2O cumulative emissions,while T1 and T2 treatments reduced the N2O cumulative emissions significantly,compared with conventional fertilization treatments(CF).3.The biogas slurry did not change the law of soil CH4 emission,but it would increase the soil CH4 emission flux.Biogas slurry irrigation would lead to higher discharge peak of soil CH4,but in the corn season were in negative emission levels;In the whole rotation cycle,the CH4 cumulative emissions of all treatments were negative,and the soil was the sink of CH4.The CH4 cumulative absorption was different,and the order of size was CK>T2>T1>CF>T3>T4.4.The addition of biogas slurry would increase the content of soil NH4+-N and NO3--N in a short time.The biogas slurry significantly increased the content of soil soluble organic carbon,and this effect was cumulative.Both biogas slurry and conventional fertilization increased the activity of soil urease,and the soil urease activity increased with the increase of irrigation times.5.The grain yield of wheat was reduced by 27.56%in T1(Wheat season irrigation biogas slurry once and corn season irrigation biogas slurry once),while the other three biogas slurry treatments did not result in the grain yield reduction,compared with conventional fertilization;The four biogas slurry treatments did not reduce the grain yield of corn,compared with the conventional fertilization.The N2O-N emission from the four biogas slurry treatments was 70.39,44.32,62.77 and 76.54 g for per tonne crop grain.6.The correlation analysis showed that the soil CO2 emission flux was positively correlated with soil DOC and atmospheric temperature.The soil N2O emission flux was positively correlated with soil DOC and NO3--N content;The soil CH4 emission flux was positively correlated with soil NH4+-N and soil water content,but negatively correlated with atmospheric temperature;And there was a significant positive correlation between soil urease activity and soil NO3--N content.In this study,under the experimental conditions,the four treatments biogas slurry irrigation modes,T2(the wheat season irrigation biogas slurry twice and corn season irrigation biogas slurry once)could ensure the crop yield while reducing CO2 and N2O emissions,increased the soil CH4-C fixation,and increased the soil DOC content,therefore,T2 was the most reasonable irrigation mode.