Study On Soil Carbon Fixation And Release Of Different Paddy-upland Rotation Crop Systems

The carbon cycle of the farmland system is an important part of the terrestrial carbon cycle and an important source of greenhouse gas emissions.Paddy-upland crop rotation is an important planting pattern in the irrigation area of the western Sichuan Plain.It is of great significance to study the effects of different paddy-upland crop rotation on fixation andemission of soil carbon.In this study,soil carbon emission and fixation in the garlic-rice（GR）model,wheat-rice（WR）model,and oil-rice（RR）model were studied in 2017-2018,and the relevant influencing factors were analyzed.The main findings are as follows:The seasonal variation of soil respiration rate in three modes was bimodal,with peaks appearing in June and September respectively.The annual mean value of soil respiration rate was GR>RR>WR.The cumulative cumulative discharge of soil respiration was GR>RR>WR,which was 193.36,157.28 and 160.27 kg·hm^-2,respectively.The daily dynamics of soil respiration showed a unimodal change,and the peak appeared between 12:00-15:00.The seasonal variation of soil methane emission rate in three modes was unimodal,with the peak occurring in July,and the annual mean value of methane emission rate was WR>GR>RR.Anniversary soil methane cumulative emissions were highest in WR mode and lowest in RR mode.The daily dynamics of soil methane emissions were mainly unimodal and bimodal,with peaks generally occurring between 12:00 and 18:00-22:00.The annual variation of total organic carbon in the three models showed a bimodal pattern with peaks occurring in May-June and December.The total organic carbon content of the three models was the highest in GR mode,the lowest in WR mode.The content of easily oxidized organic carbon is RR>GR>WR,and the content of dissolved organic carbon is GR>WR>RR.The soil organic carbon storage in the three types of GR,WR and RR increased by 6592.31、6430.77 and 3638.46kg/hm²,respectively.Correlation analysis showed that soil temperature was the main influencing factor of seasonal variation of soil respiration rate in dry season.The combination of soil water depth and soil temperature affected the change of soil respiration rate in rice season.The soil methane emission rate was significantly higher by 0-10 cm and 10-20 cm soil temperature,and there was no significant correlation with soil water content and water depth.