Evaluation of carbon, nitrogen footprint and primary energy demand under different rice production systems

Ground cover rice production system (GCRPS) has been widely proved to enhance rice yield and save irrigation water. However, information on the environmental impacts and energy consumption of GCRPS remains un-known. In this study, a two-year field experiment was conducted in Hubei Province of China including con-ventional paddy (W1) and GCRPS (W2, maintaining saturated soil water content; W3, maintaining 80% of the field capacity), factorially combined with different N management practices (N1, zero-N application; N2, single urea application; N3, split application of urea for W1 treatments; manure substitution for W2 and W3 treat-ments). By combining a soil-crop model simulation with a footprint analysis method, a life cycle inventory was built to evaluate yield-scaled carbon footprint (CF), nitrogen footprint (NF), and primary energy demand (PED) of different rice production systems. Results showed that, compared to conventional flooding paddy, GCRPSs significantly reduced CF, NF, and PED by 31%-35%, 37%-40%, and 17%-18% respectively. Across different N treatments under GCRPS, manure substitution reduced the CF (20%-22%), NF (11%-37%), and PED (25%-27%) compared to the single urea treatments. The hotspot's contribution of N2O to CF, NH3 to NF, and N-fertilizer production to PED under GCRPS can be reduced by 77%, 33%, and 51% respectively compared to the single urea treatments. Therefore, W3N3 was recommended as the best management practice achieving less CF of 541.4 kg CO2 eq t-1, NF of 2.4 kg N eq t-1, and PED of 2440.0 MJ t-1 meanwhile maintaining high rice yield of 8526 kg ha-1 in the study region.