施肥方式对紫色土农田生态系统N2O和NO排放的影响

依托紫色土施肥方式与养分循环长期试验平台(2002年—),采用静态箱-气相色谱法开展紫色土冬小麦-夏玉米轮作周期(2013年10月至2014年10月)农田生态系统N_2O和NO排放的野外原位观测试验。长期施肥方式包括单施氮肥(N)、传统猪厩肥(OM)、常规氮磷钾肥(NPK)、猪厩肥配施氮磷钾肥(OMNPK)和秸秆还田配施氮磷钾肥(RSDNPK)等5种,氮肥用量相同小麦季130 kg(N)×hm~(-2),玉米季150 kg(N)×hm~(-2)],不施肥对照(CK)用于计算排放系数,对比不同施肥方式对紫色土典型农田生态系统土壤N_2O和NO排放的影响,以期探寻紫色土农田生态系统N_2O和NO协同减排的施肥方式。结果表明,所有施肥方式下紫色土N_2O和NO排放速率波动幅度大,且均在施肥初期出现峰值;强降雨激发N_2O排放,但对NO排放无明显影响。在整个小麦-玉米轮作周期,N、OM、NPK、OMNPK和RSDNPK处理的N_2O年累积排放量分别为1.40 kg(N)×hm~(-2)、4.60 kg(N)×hm~(-2)、0.95 kg(N)×hm~(-2)、2.16kg(N)×hm~(-2)和1.41 kg(N)×hm~(-2),排放系数分别为0.41%、1.56%、0.25%、0.69%、0.42%;NO累积排放量分别为0.57 kg(N)×hm~(-2)、0.40 kg(N)×hm~(-2)、0.39 kg(N)×hm~(-2)、0.46 kg(N)×hm~(-2)和0.17 kg(N)×hm~(-2),排放系数分别为0.21%、0.15%、0.15%、0.17%、0.07%。施肥方式对紫色土N_2O和NO累积排放量具有显著影响(P0.05),与NPK处理比较,OM和OMNPK处理的N_2O排放分别增加384%和127%,同时NO排放分别增加3%和18%;RSDNPK处理的NO排放减少56%。表明长期施用猪厩肥显著增加N_2O和NO排放,而秸秆还田有效减少NO排放。研究表明,土壤温度和水分条件均显著影响小麦季N_2O和NO排放(P0.01),对玉米季N_2O和NO排放没有显著影响(P0.05),土壤无机氮含量则是在小麦-玉米轮作期N_2O和NO排放的主要限制因子(P0.01)。全量秸秆还田与化肥配合施用是紫色土农田生态系统N_2O和NO协同减排的优化施肥方式。

Effects of fertilization regimes on N2O and NO emissions from agro-ecosystem of purplish soil

Nitrous oxide (N₂O) and nitric oxide (NO) emissions from agro-ecosystem of purplish soil were measured (starting from October 2003) in a long-term purplish soil fertilization platform (established in 2002) using closed static-chamber and gas chromatography systems. Single synthetic nitrogen fertilizer (N), pig manure (OM), regular synthetic nitrogen, phosphorus and potassium fertilizer (NPK), pig manure combined with synthetic NPK fertilizer (OMNPK) and returned crop residues combined with synthetic NPK fertilizer (RSDNPK) under the same total nitrogen rate were set, and N₂O and NO emissions from croplands of purplish soil were monitored under these fertilization regimes. No fertilizer treatment (CK) was used as control in the calculations of the emission coefficients. The results showed large fluctuations in emission rates of N₂O and NO, with N₂O and NO peak emissions at the early stage of fertilization. N₂O emission was enhanced by heavy rainfall, but rainfall had no significant effect on NO emission. For the whole wheat-maize rotation period, cumulative annual emissions of N₂O in N, OM, NPK, OMNPK and RSDNPK treatments were 1.40, 4.60, 0.95, 2.16 and 1.41 kg(N)·hm^-2; and with emission coefficients of 0.41%, 1.56%, 0.25%, 0.69% and 0.42%, respectively. The cumulative emissions of NO in N, OM, NPK, OMNPK and RSDNPK treatments were 0.57, 0.40, 0.39, 0.46 and 0.17 kg(N)·hm^-2; and with emission coefficients of 0.21%, 0.15%, 0.15%, 0.17% and 0.07%, respectively. Fertilizer application regimes significantly (P< 0.05) influenced cumulative N₂O and NO emissions. Compared with conventional NPK fertilizer, pig manure amendment stimulated N₂O and NO emissions, with increases of 384% and 3% for OM and 127% and 18% for OMNPK, respectively. Returned crop residues combined with regular synthetic NPK fertilizer decreased NO emission by 56%. The application of pig manure (OM) increased N₂O and NO emissions, whereas returned crop residues plus regular synthetic NPK fertilizer (RSDNPK) decreased NO emission. The research also showed that both soil temperature and moisture conditions significantly influenced N₂O and NO emissions during wheat season (P< 0.01), but not during maize season (P> 0.05). However, soil inorganic nitrogen content was the main limiting factor for N₂O and NO emissions during the whole wheat-maize rotation year (P< 0.01). Returned crop residues plus regular NPK fertilizer was recommended as the optimal fertilization regime for simultaneous mitigation of N₂O and NO emissions.