Regulated effect of fertilization and irrigation on greenhouse gas emissions in salt-affected soil: meta-analysis

Understanding the impact of different agricultural practices on greenhouse gas (GHG) emissions in salt-affected soils is crucial for the adoption of best practices aimed not only at reducing the salt content of the soil and improving crop productivity but also at preserving the environment. A meta-analysis of 72 peer-reviewed published studies was conducted to obtain the central trend in CO₂ and N₂O emissions in response to different fertilization and irrigation practices on salt-affected soils. The results showed that high nitrogen (N) fertilizer rates (>200 kg N ha^-1) increased CO₂ and N₂O emissions by 44% and 83%, respectively, compared to low N rates (<200 kg N ha^-1). The combination of organic fertilizer and N reduced CO₂ emissions by 63% and N₂O emissions by 62% compared to those under the single application of organic fertilizer. Irrigation levels below a 60% field capacity (FC) reduced CO₂ emissions by 44% and N₂O emissions by 85%, while irrigation above a 100% FC increased CO₂ emissions by 24% and N₂O emissions by 47% compared to those under 100% FC irrigation. Nitrogen application at a rate below 200 kg N ha^-1 combined with an irrigation level below an 80% FC reduced CO₂ emissions by 2.5% and N₂O emissions by 75% compared to those under 100% FC irrigation. Positive relationships were obtained between soil salinity and GHG emissions, while CO₂ emissions decreased with increasing soil pH under fertilization practices. These results show that deficit irrigation, reduced use of nitrogen fertilizers, and the combined application of nitrogen and organic fertilizers are all practices potentially capable of reducing the greenhouse gas emissions from salt-affected soils.