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.