Abstract:

In order to explore nitrogen fertilizer management measures of low carbon production in north China, the typical summer maize field was used as the study object. The treatments included four nitrogen fertilizer rates: N0(0 kg/hm²), N1(100 kg/hm²), N2(150 kg/hm²) and N3(200 kg/hm²). The net carbon effect of different nitrogen application rates on summer maize farmland ecosystem was evaluated through statistical analysis of the test data of soil greenhouse gas emissions, indirect carbon emissions from agricultural inputs, and crop carbon sequestration. The results showed that soil CO₂ and N₂O emissions increased with the nitrogen application rate, while the CH₄ uptake decreased with the nitrogen rate increase. The carbon equivalent of total soil emissions from treatment N1, N2 and N3 increased by 14.91%, 24.19%, and 29.67% compared with that of N0, respectively. Nitrogen fertilizer input, reaching 135.27-270.55 kg/hm², contributed to a high proportion of the indirect emissions. Nitrogen application also promoted the accumulation of crop carbon sequestration, while the carbon content of net primary productivity of N0, N1, N2 and N3 reached 1965.56, 3125.68, 4345.55 and 4663.64 kg/hm², respectively. The carbon flow in agricultural system indicated that all the treatments were carbon sinks. The net carbon effect of N0, N1, N2 and N3 was 258.33, 1034.99, 2032.82, and 2192.16 kg/hm², respectively, and the carbon sustainable index reached 0.15, 0.50, 0.88 and 0.89, respectively. In summary, 200 kg/hm² nitrogen application can be recommended as an appropriate input, because it deserves more carbon sequestration in exchange for less carbon consumption, showing a higher net carbon effect.

Key words: summer maize, nitrogen application rate, farmland ecosystem, greenhouse gases, net carbon effect