N_(x)O emissions in response to the irrigation lower limits under different irrigation modes in a lettuce field

Irrigation has a significant impact on N_(x)O(N_(2)O and NO)emissions from cultivated land,yet the N_(2)O or NO emission among the irrigation lower limits under different irrigation modes has not been well compared.In an irrigated lettuce field,three DR(drip irrigation)lower limits were designed,including 75%(DR1),65%(DR2)and 55%(DR3)field capacity,and one FI(furrow irrigation)lower limit(65%field capacity).The N_(2)O and NO emission fluxes and soil nitrogen(N)forms were determined,and the linear correlation between these indicators was analyzed.Results showed that under the same irrigation regime,the N_(2)O and NO emissions from furrow irrigation treatment increased by 36.8%and 45.2%respectively compared to that from drip irrigation treatment.The cumulative N_(2)O and NO emissions under DR3 were 30.2%and 28.6%higher than under DR1,respectively.Moreover,DR1 was also the lowest among the four treatments in soil-N concentration.The N_(2)O and NO emission fluxes were more correlated to soil NH_(4)^(+)-N(r=0.88 and 0.76)or NO_(2)^(-)-N(r=0.90 and 0.80)concentration than soil-N and soluble organic N,indicating that N_(2)O and NO were mainly produced by the soil nitrification process.When the irrigation regime was the same,N_(2)O and NO emissions were lower with drip irrigation than with furrow irrigation.Besides,drip irrigation with small quota but high frequency reduced N_(2)O and NO emission compared to that with large quota but low frequency.