中国主要旱地农田N_2O背景排放量及排放系数特点

【目的】收集中国已发表的旱地农田N_2O排放田间监测文献并建立数据库,以此为基础解析中国主要旱地农田(小麦地、玉米地、蔬菜地)的N_2O背景排放值(不施肥情况下土壤的N_2O排放量)和排放系数(EF)及影响因子,为估算区域温室气体清单和提出相应的减排策略提供数据支持。【方法】利用亚组归类和回归分析等方法对主要类型旱地农田N_2O背景排放量的影响因子(如土壤全氮含量和土壤碳氮比)及影响EF的因子(如氮肥用量及肥料类型——硝化抑制剂和缓控释肥)进行分析。【结果】(1)中国旱地农田N_2O背景排放量为0.70—3.14 kg N_2O-N·hm~(-2);小麦地和夏玉米地的N_2O背景排放量和蔬菜地的N_2O日背景排放量均随土壤全氮含量增加而增加,并随土壤碳氮比的增加而降低,灌溉促进小麦地N_2O背景排放量增加;(2)EF随着无机氮肥用量的增加而增加,不同作物种植类型农田的EF大小依次为蔬菜地(0.61%—1.13%)夏玉米地(0.50%—0.68%)春玉米地(0.35%—0.40%)小麦地(0.22%—0.36%);夏玉米地的EF是小麦地的2倍左右;(3)使用不同种类硝化抑制剂后氮肥的EF均有不同程度的降低,EF降低了34%—60%,EF降低程度依次为:DCD+HQ(58.9%)NBPT+DCD(52.9%)DMPP(51.1%)NBPT(44.1%)吡啶(39.5%)DCD(38.9%);硝化抑制剂降低EF的效果在不同旱地农田的表现为:小麦地(60.0%)蔬菜地(50.6%)春玉米地(39.6%)夏玉米地(34.7%);(4)与常规尿素相比,不同类型缓控释肥使得EF降低了15.9%—78.9%,降低次序依次为:长效碳酸氢铵(78.9%)聚合物包膜尿素(59.8%)脲甲醛(53.4%)树脂包膜尿素(44.9%)硫磺包膜尿素(30.6%)钙镁磷肥包膜尿素(15.9%);缓控释肥降低EF的效果在不同农田表现为:蔬菜地(78.4%)春玉米地(58.2%)小麦地(49.2%)夏玉米地,控释肥在降低夏玉米地EF的作用较小。【结论】旱地农田N_2O排放主要受土壤养分状况(全氮含量和碳氮比)和管理措施(灌溉和施肥)及其他因素的共同影响,应依据不同气候生态区的气候和土壤特点以及作物类型并考虑氮肥用量和类型采取针对性的减排措施,以有效降低农田N_2O排放。

Characteristics of Background Emissions and Emission Factors N2O from Major Upland Fields in China

【Objective】Published literatures regarding to N₂O emissions from upland fields in China were collected to establish a dataset. The established database was used to analyze the N₂O background emissions (emission from soil without fertilization), emission factors (EFs) and associated factors influencing the N₂O emissions from major upland fields (for example wheat fields, maize fields and vegetable fields) in China. The results will provide supports for estimating regional N₂O emission inventory and provide appropriate mitigation strategies.【Method】Subgrouping analysis and regression analysis were used to analyze the factors which influence N₂O background emissions (for example the soil nitrogen content and C﹕N ratio of the soil) and EFs (for example the nitrogen application level and fertilizer types such as nitrification inhibitors and slow release or controlled release fertilizers).【Result】(1) The N₂O background emissions from upland fields ranged between 0.70 and 3.14 kg N₂O-N·hm^-2. Either N₂O background emissions from wheat and summer maize fields or daily N₂O background emissions from vegetable fields increased with increasing soil total N (TN) while decreased with the increasing of soil C﹕N ratio. Irrigation could promote the N₂O background emissions from wheat fields. (2) EFs increased with increasing N application rate and its value was 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 were two times higher than those from wheat fields. (3) Nitrification inhibitors could 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 (38.9%). The effects of different nitrification inhibitors on EF decline were 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) Compared with normal urea, slow release or controlled release fertilizers decreased EF to an 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 release or controlled release fertilizers on decreasing EFs varied in 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 release or controlled release fertilizers on decreasing EFs were lower in summer maize fields than in other croplands.【Conclusion】N₂O emissions are influenced by many factors including soil properties (i.e. soil TN content and C: N ratio), management practices (i.e. irrigation and fertilization) and other factors. In order to reduce N₂O emissions, it is critical to take appropriate practices specific to oriented climate, soil and cropping regimes and combined with appropriate rational nitrogen fertilizer application rate and type.