Long term response and adaptation of farmland water, carbon and nitrogen balances to climate change in arid to semi-arid regions

Climate change poses a challenge for resource utilization and environmental pollution issues caused by agricultural production, especially in arid to semi-arid regions. Farmland water, carbon and nitrogen (WCN) balances are closely related to these resource and environmental issues. Thus, the Agro-Hydrological & chemical and Crop systems simulator (AHC) was used to assess the response of WCN balances to climate change in a spring wheat farmland of arid Northwest China and to propose adaptation strategies. Five Global Climate Models from the Coupled Model Intercomparison Project 6 and two Shared Socioeconomic Pathways (SSP1-2.6 and SSP5-8.5) were used to establish scenarios with the AHC model to simulate farmland WCN balances for the 2025–2100 period. Various irrigation amounts and nitrogen fertilization rates were tested as compensation strategies. Results indicated that precipitation showed an increasing trend, thus percolation increased and soil water consumption decreased from 2025 to 2100. However, for the carbon budget, although the soil CO₂ emissions tend to decrease, the net primary production (NPP) was also significantly reduced, which resulted in declining the net ecosystem carbon budget (NECB) under future climatic conditions. In addition, higher temperature and increased precipitation enhanced soil inorganic nitrogen leaching and N₂O emissions but reduced NH₃ volatilization from 2025 to 2100. Overall, the soil total nitrogen loss was increased over time, whereas crop nitrogen uptake (CNU) was significantly reduced. In relation to the SSP1-2.6 scenario, the SSP5-8.5 scenario accelerated the increase rates of soil water percolation and total nitrogen loss over time, as well as the decrease rates of CNU and NPP over time. The negative effects caused by climate change can be mitigated by reducing irrigation and increasing nitrogen fertilization. For the SSP1-2.6 scenario, 30% irrigation reduction and 30% nitrogen fertilization increase can effectively decrease soil water percolation and the related nitrogen losses while CNU, NPP and NECB increase in relation to the current management (240 mm irrigation and 200 kg ha^–1 nitrogen fertilization). For SSP5-8.5 the strategy with 45% irrigation reduction and 45% nitrogen fertilization increase can also decrease nitrogen losses and increase CNU, NPP and NECB.