Effects of continuous overturning of ryegrass on diurnal variation of CO2 in tobacco-growing soil profile in central Henan Province
[Objectives]In order to investigate the effects of overturning ryegrass on soil respiration rate and daily carbon dioxide(CO2)emissions in soil profile during the growth of flue-cured tobacco in central Henan Province,and the relationship between them and environmental factors,the best time for CO2 collection and observation was determined.[Methods]In 2021,two treatments were set up in Zhengzhou Science and Education Park of Henan Agricultural University(relying on long-term positioning experiment),and nitrogen,phosphorus and potassium fertilizer(NPK)and nitrogen,phosphorus and potassium + planting and flipping ryegrass(NPKG)were applied.The daily change process of CO2 emissions in tobacco fields were measured every 30 days after tobacco seedling transplantation.[Results]① From 0 to 10 cm,the soil temperature and soil respiration rate displayed a unimodal or bimodal pattern with highs during the day and lows at night.The soil respiration rate of NPKG treatment was significantly higher than that of NPK treatment,and the correction coefficients at 9:00 and 21:00 were closest to 1,and there was no significant difference between NPKG treatment and NPK treatment.②With the deepening of soil layer,CO2 concentration increased,CO2 diffusion flux decreased,and the CO2 concentration and emission flux under NPKG treatment were higher than those under NPK treatment.CO2 concentration in the 0,5,10,and 20 cm soil layers,along with the diffusion flux in the 0～20 cm soil layers,exhibited distinct diurnal variation characteristics,and the CO2 concentration at 90 days was lower than that at 60 days.③ There was a significant or extremely significant positive correlation between soil respiration rate and CO2 diffusion flux in 0-20 cm soil layer.[Conclusion]Ryegrass overturning increased soil respiration rate,CO2 concentration and CO2 diffusion flux in different soil layers.Around 9:00 and 21:00 are the optimal sampling periods,and the diurnal variation characteristics of CO2 concentration in 5 cm and 10 cm soil layers and diffusion flux in 5～10 cm soil layers were similar to soil respiration rate.The highest CO2 concentration was found on day 60,followed by day 30.The soil respiration rate can be predicted based on soil CO2 concentration.
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