Optimizing drip irrigation and nitrogen fertilization regimes to reduce greenhouse gas emissions, increase net ecosystem carbon budget and reduce carbon footprint in saline cotton fields

The arid and semi-arid regions of northwest China play a crucial role in ensuring the national cotton production. Soil water potential (SWP)-based deficit irrigation is potentially an effective irrigation strategy in maintaining agricultural productivity in these regions. However, the impact of various SWP thresholds and nitrogen application rates on carbon balance and environmentally friendly economic benefits in cotton systems remains unclear. A two-year field experiment was conducted to investigate the effects of three SWP thresholds (W1, W2 and W3: −30, −20 and −10 kPa) and three nitrogen rates (F1, F2 and F3: 200, 300 and 400 kg ha−1) on greenhouse gas (GHG) emissions, seed cotton yield, carbon storage, and economic benefits in drip-fertigated saline cotton fields. The results showed that increasing nitrogen rate significantly increased N2O emission, while higher irrigation level reduced the soil's capacity to absorb CH4. Moreover, increasing irrigation level and nitrogen rate led to higher soil CO2 emission. The W3F3 obtained the highest seed cotton yield, ranging from 6529.6 to 6804.6 kg ha−1. Nitrogen application increased soil organic carbon storage by 5.6–12.5 %, whereas excessive nitrogen fertilization resulted in significant losses in soil inorganic carbon, ranging from 20.7 % to 34.9 %. The W2F2 enhanced net ecosystem carbon budget accumulation by increasing the input efficiency of carbon and reducing GHG emissions, and excessive GHG emissions limited the net ecosystem carbon budget of high-fertilization treatments. Meanwhile, the increased fertilizer and environmental costs reduced net ecosystem economic benefit. Fertilizer was identified as the major contributor to the ecosystem carbon footprint, accounting for more than 22.9 %. In conclusion, the W2F2 not only obtained the optimal soil carbon sequestration and carbon balance in the system, but also generated economic profits comparable to those of the high-fertilization treatments while producing lower direct GHG emissions. These findings highlight the significance of rational drip irrigation and nitrogen fertilization in maintaining high productivity and carbon sustainability in saline cotton fields.