Analyses On Emission Factors And Effect Factors Of N₂O And CH₄ From Main Cropland Soils In China

CH4 and N2O are two major greenhouse gases after CO2, farmland is an important source of CH4 and N2O emissions, thus it has important meaning for global warming and climate change to reduce agricultural CH4 and N2O emissions. Published literatures regarding to N2O emissions from upland fields and CH4 and N2O from paddy fields in China are collected to establish a dataset. Through those methods of Subgrouping analyses, regression analyses and factorial analysis and so on, respectively the established database is used to analyze the N2O background emissions, emission factors (EFs) and associated factors influencing the N2O emissions from major upland fields (for example wheat fields, maize fields and vegetable fields), the CH4 and N2O daily emissions, global warming pootential (GWP) and associated factors influencing the CH4 and N2O emissions from paddy fields in China. The results shall provide support for estimating regional N2O emission inventory and providing appropriate mitigation strategies. The main results from this study are presented as follows:1. The results of characteristics of background emissions and emission factors of N2O from major upland fields shows:(1) The N2O background emissions from upland fields range between 0.70 kgN2O-N·hm-2 and 3.14 kgN2O-N·hm-2. Either N2O background emissions from wheat and summer maize fields or daily N2O background emissions from vegetable fields increase with increasing soil total N (TN) while decrease with the increasing of soil C:N ratio. Irrigation can promote the N2O background emissions from wheat fields.(2) EFs increase with increasing N application rate and its value is ranked in the following order: vegetable fields (0.56%-0.61%)>summer maize fields (0.50%-0.68%)>spring maize fields (0.35%-0.40%) > wheat fields (0.22%-0.36%). EFs from summer maize fields are one times higher than those from wheat fields.(3) Nitrification inhibitors can decrease N2O EF by 34%-60% ranking in the order:DCD+HQ (58.9%)>NBPT+DCD(52.9%)>DMPP(51.1%)>NBPT(44.1%)>Pyridine (39.5%)>DCD (39%). The extent of different nitrification inhibitors on EF decline are varied in different fields ranking in the order: wheat fields(60.0%)>vegetable fields(50.6%)>spring fields(39.6%)>summer maize fields(34.7%).(4) Slow-released or control-released fertilizers decrease EF to the extent between 15.9% and 79% ranking in the order:long-effect ammonium bicarbonate (78.9%)> Polymer-coated urea (59.8%)> Urea formaldehyde (53.4%)> Resin-coated urea (44.9%)> Sulfur-coated urea (30.6%)> Calcium-magnesium-phosphate-coated urea (15.9%). The decline effects of different slow-released or control-released fertilizers on decreasing EFs vary in the different fields ranking in the order:vegetable fields (78.4%)> spring maize fields (58.2%)> winter wheat fields (49.2%)> summer maize fields. The effect of slow-released or control-released fertilizers on decreasing EFs are lower in summer maize fields than in other croplands.2. The analysis results of the CH4 and N2O daily emissions and globle warming potential (GWP) from paddy fields in China showed that:(1) CH4 daily emissions and GWP of CH4 under fertilizer and water management both are increased with increasing soil organic matter (SOM) from early paddy fields, late paddy fields and single harvesting paddy fields;(2) CH4 daily emissions under different type paddy fields are ranked in the following order:single harvesting paddy fields (0.78-6.19 kg CH4·hm-2 d-1)>late paddy fields (double cropping) (0.52-3.80 kg CH4·hm-2 d-1)> early paddy fields (1.02-3.45 kg CH4·hm-2 d-1)> late paddy fields (rice-wheat rotation)(0.48-1.86 kg CH4-hm-2 d-1); Compared CH4 daily emissions from early and late paddy fields of double cropping paddy fields indicate that later more than former under fertilizer management; GWP of CH4 and N2O from late paddy fields are more than early paddy fields across all water managements; rice-wheat rotation can reduce the emissions of CH4 and N2O;(3) CH4 daily emissions in different fertilizer types from early paddy fields, late paddy fields and single harvesting paddy fields are ranked in the following order:Straw turnover> Chemical nitrogen fertilizer with organic manure> Chemical nitrogen fertilizer ≈Biochar; Compared with straw turnover, compare chemical nitrogen fertilizer with organic manure and biochar find that applying biochar can reduce CH4 emissions significantly;(4) Controlling water management model (Long-term flooding:CF; Flooding-Aeration-Rehydration-Dry fall:F-D-F; Flooding-Aeration-Alternating wet and dry-Dry fall:F-D-F-M; Control irrigation:CI) can reduce greenhouse gas emissions significantly from rice paddies, and controlling water management properly can reduce comprehensive GWP of CH4 and N2O significantly shows:CF>F-D-F> F-D-F-M>CI, and GWP of CH4 from early paddy fields, late paddy fields and single harvesting paddy fields are ranked in the following order:CF>F-D-F>F-D-F-M>CI, GWP of N2O are ranked in the following order:CF<F-D-F<F-D-F-M<CI;In summary, N2O and CH4 emissions from agricultural soil are influenced by many factors commonly, agricultural management activities (water and fertilizer management, fertilizer amount, fertilizer types) play a major role in agricultural greenhouse gases emissions which are influenced by soil nutrient conditions (soil SOM content and C:N ratio) and climatic conditions (crop growth period, temperature and precipitation in growth period); management practices (i.e. fertilizer and water management), rotation system and other factors instead of univariate. In order to obtain a more accurate inventory of greenhouse gas emissions and propose effective classification mitigation policy, it is critical to take appropriate practices specific to oriented climate, soil conditon and cropping regimes and combined with appropriate rational nitrogen fertilizer application rate and type and water management.