Distribution characteristics of nitrous oxide, methane and carbon dioxide along soil profile in typical vegetable fields

The concentrations of nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂) at 7 cm, 15 cm, 30 cm and 50 cm soil depths under bare fallow, rotation field?Ⅰ (rotation of celery-tung choy-baby bok choy-amaranth) and rotation field?Ⅱ (rotation of choy sum-celery-tung choy-bok choy) were monitored using a special in situ soil gas collection device and gas chromatography to explore the distribution characteristics of N₂O, CH₄ and CO₂ in soil profiles. The results showed great variations in annual concentrations of N₂O, CH₄ and CO₂ within the 0-50 cm soil depth with respective values of 0.63 1 657.0 μL(N₂O)L^-1, 0.872.5 μL(CH₄)L^-1 and 0.4136.6 mL(CO₂)L^-1. N₂O concentrations under rotation?Ⅰ?and rotation?Ⅱ increased with increasing soil depth. Also N₂O concentration under bare fallow increased with increasing soil depth within the 030 cm soil layer, while it decreased with increasing depth within the 3050 cm soil layer. Average N₂O concentrations of two vegetable rotational fields were significantly higher than that of bare fallow. Different N fertilizers application to the two vegetable rotational fields did not significantly change N₂O concentration for the same soil layer. The orders of both CH₄ and CO₂ concentrations in soil profile were 50 cm > 30 cm > 15 cm > 7 cm. N fertilizer application had no significant effect on CH₄ concentration. Average CH₄ concentration under the two vegetable rotations in the 015 cm soil depth was higher than that under bare fallow. However, CH₄ concentration at the 1550 cm soil depth was higher under field rotation Ⅰ but lower under field rotation Ⅱ than that under bare fallow. CO₂ concentration had a clear seasonal variation. Average CO₂ concentration under the two vegetable rotations was lower than that in corresponding soil layers under bare fallow, except for the 50 cm soil depth under field rotation Ⅰ. The results suggested that soil N₂O, CH₄ and CO₂ concentrations of vegetable rotational fields with high nitrogen input and frequent tillage had greater temporal and spatial variability. The effect of nitrogen application on N₂O was stronger than that on CH₄ and CO₂. Nitrogen application and tillage slightly affected the distribution of CH₄ concentration in the soil. CO₂ concentration was significantly affected by soil temperature and tillage. Other factors affected the distribution of N₂O, CH₄ and CO₂ in the soil can be the focus of further research.