[Effects of the Crop Rotation on Greenhouse Gases from Flooded Paddy Fields]

A field experiment was conducted at the Key Field Station for Monitoring Eco-environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University, Chongqing. The static chamber and gas chromatography method was used to study the effect of the cropping systems on greenhouse gases from rice-fallow (RF), rice-rapeseed rotation (RR), and rice-brussel mustard rotation (RV) cropland in situ for a year. An opaque chamber was used for CH₄ and N₂O observations and a transparent chamber was utilized for CO₂ observations. The results show that the annual cumulative CH₄ emissions from different crop rotations were (CH₄, kg·hm^-2) RF (422.87±27.1) > RR (132.05±23.11) > RV (50.91±3.83). The RV and RR were significantly lower than RF (P<0.05). The annual cumulative emissions of N₂O[N₂O, kg·hm^-2] were RV (21.38±6.51) > RR (20.02±5.23) > RF (0.48±0.02). The RV and RR were significantly higher than RF (P<0.05). The annual net cumulative emissions of CO₂ were (CO₂, t·hm^-2) RR (-55.43±5.04) > RV (-29.1±3.00) > RF (-14.08±1.81). The RV and RR were significantly higher than RF (P<0.05). At the time scale of 100 a, the integrated global warming potentials (GWP) of CH₄, N₂O, and CO₂ were (CO₂, t·hm^-2)RR(-46.43) > RV(-22.01) > RF(-2.11), indicating that converting flooded paddy fields to paddy-upland crop rotation systems notably increases the potential increment of carbon sinks. Compared with RV, RR has a better effect, which suggests that rice-rapeseed rotation is the most effective measure for the escalation of carbon sinks of ecosystems in the southwestern area.