A global meta-analysis of nitrous oxide emission from drip-irrigated cropping system

Drip irrigation is a useful practice to enhance water and fertilizer nitrogen (N) use efficiency. However, the use of drip irrigation to mitigate nitrous oxide (N₂ O) emissions in agricultural systems globally is uncertain. Here, we performed a global meta-analysis of 485 field measurements of N₂ O emissions from 74 peer-reviewed publications prior to March 2021, to quantify the fertilizer-induced N₂ O emission factor (EF) of drip irrigation and examine the influencing factors of climate, crop, soil properties, and source and rate of fertilizer N application. The results showed that drip irrigation reduced (p < 0.05) N₂ O emissions by 32% and 46% compared to furrow and sprinkler irrigation systems, respectively. The overall average EF with drip irrigation was 0.35%, being two-thirds lower than the IPCC Tier I default value of 1% (kg N₂ O-N/kg added fertilizer N). The EF was not significantly affected by climate, crop, soil texture, soil organic carbon content, and pH. The EF was also not significantly (p > 0.05) affected by synthetic N fertilizer source despite a lower numerical value with enhanced efficiency than conventional fertilizers. The EF increased significantly (p < 0.001) with N addition rate in a binomial distribution. Using the IPCC default EF overestimated N₂ O emissions inventories for drip-irrigated cropping systems by 7614 and 13,091 Mg per year for China and the globe, respectively. These results indicate that drip irrigation should be recommended as an essential N₂ O mitigation strategy for irrigated crop production.