Reducing carbon footprints and increasing net ecosystem economic benefits through dense planting with less nitrogen in double-cropping rice systems.

ABSTRACT

Excessive application of nitrogen fertilization in farmland systems can cause nitrogen wastage, environmental pollution, and increase greenhouse gas (GHG) emissions. Dense planting is one of the efficient strategies for nitrogen fertilizer reduction within rice production. However, there are paying weak attention to the integrative effect of dense planting with less nitrogen (DPLN) on carbon footprint (CF), net ecosystem economic benefit (NEEB) and its components in double-cropping rice systems. Herein, this work aims to elucidate the effect via field experiments in double-cropping rice cultivation region with the treatments set to conventional cultivation (CK), three treatments of DPLN (DR1, 14 % nitrogen reduction and 40,000 hills per ha density increase from CK; DR2, 28 % nitrogen reduction and 80,000 hills density increase; DR3, 42 % nitrogen reduction and 120,000 hills density increase), and one treatment of no nitrogen (N0). Results showed that DPLN significantly reduced average CH4 emissions by 7.56 %-36 %, while increasing annual rice yield by 2.16 %-12.37 % compared to CK. Furthermore, the paddy ecosystem under DPLN served as a carbon sink. Compared with CK, DR3 increased gross primary productivity (GPP) by 16.04 % while decreasing direct GHG emissions by 13.1 %. The highest NEEB was observed in DR3, which was 25.38 % greater than CK and 1.04-fold higher than N0. Therefore, direct GHG emissions and carbon fixation of GPP were key contributors to CF in double-cropping rice systems. Our results verified that optimizing DPLN strategies can effectively increase economic benefits and reduce net GHG emissions. DR3 achieved an optimal synergy between reducing CF and enhancing NEEB in double-cropping rice systems.