Effect of low nitrogen application and soybean intercrop on soil greenhouse gas emission of sugarcane field

This study discussed the effect of different sugarcane intercropping patterns and nitrogen dosages on soils greenhouse gas emission and the related impact on crops yield. The study further strengthened the theoretical basis for measuring agriculture-based greenhouse gas emission. It analyzed emission fluxes of greenhouse gases (CO₂, N₂O and CH₄) in sugarcane//soybean intercropping systems with crops line ratios of 1∶1 (SB1) and 1∶2 (SB2), monocropped sole sugarcane(MS)under two nitrogen levels (N2, 525 kg·hm^-2 and N1, 300 kg·hm^-2) and monocropped soybean under zero nitrogen supply using the static chamber/gas chromatographic technique during the crop growth season. Results showed that compared to the sugarcane monoculture, cumulative emissions of CO₂ and N₂O in SB2 under low nitrogen dose (SB2-N1) respectively decreased by 35.58% and 56.36%. Also cumulative CH₄ emission increased by 7.02%. Soils in different cropping patterns and nitrogen dosages served as sources of CO₂ and N₂O, sink of CH₄ during crop growth season. After nitrogen application, CH₄ absorption rate decreased while CO₂ and N₂O flux rates increased. CO₂ emissions (kg·hm^-2·a^-1) under MS-N1, SB1-N1, SB2-N1, MS-N2, SB1-N2, SB2-N2 and MB treatments were 5 096.89, 6 422.69, 3 283.20, 4 103.29, 4 475.84, 4 775.31 and 4 780.35, respectively. Cumulative N₂O emissions (kg·hm^-2·a^-1) under MS-N1, SB1-N1, SB2-N1, MS-N2, SB1-N2, SB2-N2 and MB treatments were 4.61, 5.11, 2.15, 3.13, 3.72, 5.60 and 3.11, respectively. Also cumulative CH₄ emissions (kg·hm^-2·a^-1) under MS-N1, SB1-N1, SB2-N1, MS-N2, SB1-N2, SB2-N2 and MB treatments were 13.68, 21.78, 12.72, 5.53, 11.36, 4.77 and 9.97, respectively. Land equivalent ratio (LER) values in sugarcane//soybean intercropping systems exceeded 1.0 during 2009 and 2012. The study showed that SB2 cropping system was the best one under low nitrogen conditions.