Impacts of cropping systems on soil carbon and nitrogen stocks and greenhouse gas emissions in flooded rice systems

Flooded rice systems are important sources of methane (CH 4 ) emissions and potential sinks of soil carbon (C), depending on management practices. However, the combined effects of cropping system on greenhouse gas (GHG) emissions and soil C and nitrogen (N) stock dynamics in subtropical paddy soils remain poorly understood. This study assessed the effect of cropping systems differing in soil disturbance intensity and crop diversity on (i) soil C and N stocks (0–30 cm), (ii) CH 4 and nitrous oxide (N 2 O) emissions during the rice growing and off-season, and (iii) net global warming potential (GWP) over a four-year period in subtropical paddy soil. A field experiment compared continuous rice and diversified systems, including summer fallow and soybean rotation. Soil C and N stocks showed no significant differences among treatments over the four years, although lower residue inputs in fallow or soybean systems tended to decrease C in the 0–5 cm layer, mainly affecting particulate organic C. CH 4 emissions were highest in continuous rice systems (404 kg ha −1 ), associated with high straw inputs and frequent flooding, and lowest in soybean or summer fallow systems (195 kg ha −1 ). N 2 O emissions were low, episodic, and not consistently influenced by cropping systems. Consequently, net GWP was driven mainly by CH 4 , with continuous rice systems showing the highest values (48.9 Mg CO 2 eq ha −1 ). Incorporating soybean into rice rotations reduced net GWP by up to 55% compared to continuous rice. These findings demonstrate that crop rotation can substantially mitigate CH 4 emissions from subtropical paddy soil without compromising soil C and N stocks in the short-term.