Effects of nitrogen fertilizer, soil temperature and moisture on the soil-surface CO2 efflux and production in an oasis cotton field in arid northwestern China.

In several studies of agricultural ecosystems, researchers have focused on the soil-surface carbon dioxide (CO 2 ) effluxes, but the nature of CO 2 production in the soil profile and its influencing factors remain unclear. In this study, the soil-surface CO 2 effluxes in an oasis cotton field were measured using the chamber method, and the CO 2 concentrations were used to estimate the CO 2 production in different layers of the soil profile using the gradient method. The soil CO 2 concentrations increased with increasing soil depth, whereas CO 2 production decreased with increasing soil depth. Both soil-surface CO 2 effluxes and CO 2 production in the 0–40 cm layers exponentially increased with increasing temperature. Irrigation temporarily reduced the soil-surface CO 2 effluxes by 19–63% through inhibiting CO 2 production in the 10–40 cm layer but did not affect the CO 2 production in the 0–10 cm layer. CO 2 production mainly occurred in the 0–10 cm layer, and this cumulative production accounted for 63–67% of the total production throughout the soil profile (0–40 cm). The application of nitrogen (N) fertilizer enhanced the rate of CO 2 production in the 0–20 cm layer by increasing the root biomass and soil mineral N content. A positive correlation was detected between the soil-surface CO 2 efflux and soil NO 3 − content in 2015, but no significant correlations were found between the soil-surface CO 2 efflux and soil NH 4 + contents in any treatment. A higher soil-surface CO 2 efflux was observed under high soil temperature and a certain soil moisture range (0.21–0.23 cm 3 cm − 3 ). An analysis of the soil profile revealed higher CO 2 production rates detected in the 0–10 cm layer under high soil temperature and moisture conditions, but higher rates were observed under high soil temperature and low soil moisture conditions in the 10–20 cm layer. Therefore, our results suggest that the effects of fertilization, soil temperature and moisture on CO 2 production vary depending on the soil depth. These findings might improve our understanding of the mechanisms underlying soil respiration in soil profiles. [ABSTRACT FROM AUTHOR]