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The ridge–furrow rainwater harvesting (RFRH) planting mode is widely used in arid and semi-arid areas to solve the problems of agricultural water shortage and low productivity. However, the impact of film mulching on the stability of soil carbon pools makes this planting mode vulnerable to the risk of increased soil carbon emissions and carbon pool losses. In order to clarify the relationship between soil carbon emissions and hydrothermal factors, as well as the regulatory effect of biochar application on soil carbon sequestration and reduced emissions under this planting mode, we set up a biochar application experiment. The effects of the biochar application (at 10 Mg ha−1 biochar and 20 Mg ha−1 biochar) on the soil water dynamics, soil temperature changes, CO2-C and CH4-C flux dynamics, grain yield, carbon emission efficiency, and the net ecosystem carbon budget in wheat fields under the RFRH planting mode were investigated, with no biochar application as the control. The results showed that applying biochar increased the soil water content, soil average temperature, cumulative CH4-C uptake, wheat grain yield, and carbon emission efficiency by 3.10–12.23%, 0.98–3.53%, 59.27–106.65%, 3.51–16.42%, and 18.52–61.17%, respectively; reduced the cumulative CO2-C emissions by 7.51–31.07%; and increased the net ecosystem carbon budget by 2.91 Mg C ha−1 to 6.06 Mg C ha−1. The results obtained by equation fitting showed that in wheat fields under RFRH, the CO2-C emission fluxes had negative and positive exponential relationships with the soil water content and soil temperature, respectively, while the CH4-C uptake fluxes had no significant correlation with the soil water content and had an inverse U-shaped quadratic function relationship with soil temperature. Overall, these results suggest that the application of biochar to wheat fields under RFRH can improve grain yield, farmland carbon emission efficiency, and the net ecosystem carbon budget, and change wheat fields from a carbon source to a carbon sink. These results can provide a theoretical basis and technical support for efficient, green, and sustainable production in farmland in arid and semi-arid areas.

Studying carbon dioxide fluxes in wheat fields is becoming increasingly important. The dry, semi-humid area in China is an important wheat production area, but the variations in carbon dioxide fluxes in wheat fields and the mechanisms associated with the carbon dioxide flux response to meteorological factors and water–nitrogen management have rarely been studied systematically in this area. Thus, we conducted a monitoring experiment in order to clarify the responses of CO2-C fluxes to meteorological factors and water-and-nitrogen management in wheat fields in this dry, semi-humid area, and modeled the relationships between CO2-C fluxes and meteorological factors under different water-and-nitrogen managements. Four water-and-nitrogen treatments were tested in wheat fields: rain-fed (no water and nitrogen added), irrigation (150 mm water added), rain-fed plus nitrogen application (225 kg ha−1 nitrogen added), and irrigation plus nitrogen application (150 mm water and 225 kg ha−1 nitrogen added). The CO2-C fluxes and meteorological indicators were monitored and analyzed, before fitting the relationships between them. The direct and total effects of precipitation, air temperature, and water vapor pressure on CO2-C fluxes in wheat fields were all positive, and their total effect coefficients were more than 0.7 and significant. Irrigation and nitrogen application increased the CO2-C fluxes in wheat fields by 6.82–14.52% and 51.59–55.94%, respectively. The fitting results showed that partial least squares regression models of the relationships between meteorological factors and CO2-C fluxes in wheat fields under different treatments were all effective, with R2Y (cum) and Q2 (cum) values around 0.7. Overall, these results suggest that precipitation, air temperature, water vapor pressure, and water and nitrogen addition have positive effects on CO2-C fluxes from wheat fields in dry, semi-humid areas. The partial least squares regression method is also suitable for modeling the relationships between meteorological factors and CO2-C fluxes. These results may provide a scientific basis for predicting and regulating CO2-C fluxes in wheat fields in dry, semi-humid areas, and provide a methodological reference for ecosystem carbon dioxide flux simulation studies.

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