Effects of irrigation methods and salinity on CO₂ emissions from farmland soil during growth and fallow periods

Drip irrigation and brackish water irrigation are considered to be the two main ways to alleviate the current shortage of agricultural freshwater resources and have been widely used in countries around the world. Our purpose is to evaluate the effects of different irrigation methods (flood irrigation and drip irrigation) and irrigation water salinities (1.1 g·L^-1, 2.0 g·L^-1, 3.5 g·L^-1, and 5.0 g·L^-1) on the soil CO₂ emissions during the growth and fallow periods of spring maize. Therefore, a two-year field experiment was conducted in Hetao Irrigation District in China from 2017 to 2019. The results showed that compared with flood irrigation, drip irrigation significantly decreased the soil CO₂ emissions in the growth period. After irrigation with a salinity of 5.0 g·L^-1, the soil moisture was the highest because the plant water absorption was inhabited by soil salt, and the soil CO₂ emissions were also promoted during the growth period. Irrigation method and irrigation water salinity had no effect on the soil CO₂ emissions in the fallow period. Soil temperature, moisture and inorganic nitrogen content were the main factors affecting the daily CO₂ emission flux. The soil CO₂ emissions during the growth period accounted for more than 83.93% of the annual soil emissions. Based on the goal of saving freshwater resources, ensuring soil safety, reducing soil CO₂ emissions and increasing the size of the carbon pool, adoption of drip irrigation with 2.0 g·L^-1 brackish water could be adopted to ensure the sustainable development of local agriculture.