Diurnal and seasonal soil CO2 flux patterns in spring maize fields on the Loess Plateau, China

Carbon dioxide flux from the soil to the atmosphere is an important component of terrestrial C cycling, and accurate estimates of CO2-C fluxes are crucial for estimating C budgets. A field study was conducted (i) to examine the diurnal and seasonal soil CO2 flux pattern in spring maize fields on the Loess Plateau, and (ii) to determine the effects of soil characteristics affected by various cultivation practices on CO2 flux from the soil surface to the atmosphere. Soil surface CO2 flux was determined with an LI-8100 Automated Soil Flux System, and related environmental factors were also measured, including near-ground air temperature and relative humidity, soil moisture (0-15 cm), soil temperature (at depths of 5, 10, 15, and 20 cm), and leaf area index. Diurnal soil CO2 flux showed a single peak between 12-00 h and 16-00 h, and reached a minimum in the early morning, at about 4-00 h. During the crop's growing season, soil CO2 flux increased during the rapid vegetative growth stages, reached its maximum during the peak reproductive stages, and then declined as the plants senesced. Time series analysis showed that the temporal dynamics of the CO2 flux were more closely related to air temperature than to soil temperature; this may be because a substantial portion of the CO2 originated from surface residues. The time-averaged mean soil CO2 flux for different cultivation practices over the growing season was ranked as follows: plastic film mulching (3.980 mmol m(-2) s(-1)) > corn straw mulching (3.464 mmol m(-2) s(-1)) > supplementary irrigating (3.157 mmol m(-2) s(-1)) > rain-fed (2.371 mmol m(-2) s(-1)) > bare ground (1.934 mmol m(-2) s(-1)). Different cultivation practices affected plant and microbial activities, and soil hydrothermal conditions, and caused different patterns of soil surface CO2 flux in spring maize fields on the Loess Plateau.