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A pot experiment was performed to estimate the effect of maize (Zea mays L.) straw biochar application on nitrous oxide (N 2 O) and methane (CH 4 ) emissions, N 2 O emission factors and vegetable yield through cultivation of choy sum (Brassica rapa L. ssp. chinensis) and amaranth (Amaranthus mangostanus L.) for 99 days in 2011 at Nanjing, China. Eight treatments were established as follows: control (CK), 100% urea nitrogen (N) (Urea), urea and manure N at 5:5 (UM1) or 7:3 (UM2) combination, biochar incorporation with urea at 20 Mg ha À1 (UB1) or 40 Mg ha À1 (UB2) and biochar incorporation at 30 Mg ha À1 with UM1 (UM1B) or UM2 (UM2B). UB1, UB2, UM1B and UM2B significantly decreased N 2 O emission by 77% to 86%, while UM1 and UM2 did not show significant N 2 O emission difference in comparison with Urea. CH 4 emissions were not affected by biochar amendment or manure application. On average, UM1B and UM2B significantly enhanced vegetable production by 32, 48 and 28% as compared to Urea, average UM1/UM2 and average UB1/UB2, respectively. N 2 O-N emission factors with biochar application were 0.4-0.7%, while those without biochar being 2.5-3.2%. Comprehensively considering vegetable yield, N 2 O emission, CH 4 emission and N 2 O-N emission factor, the most effective combination in this study was biochar at 30 Mg ha À1 when applied with chemical N fertilizer and manure. In conclusion, biochar application greatly reduced N 2 O emissions and N 2 O-N emission factors while maintaining vegetable production.

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