Rice-wheat Rotation Farmland Wheat Growing Season, Soil Air Of Co <sub> 2 </ Sub> Concentration And Its Main Impact Factor Research

Assessing the dymatics of gaseous production in soils is of interesting because they are important sources and sinks of greenhouse gases.Changes in soil air corbon dioxide(CO2) concentrations were studied in a rice-wheat rotation ecosystem of southeast China.Concentr-ations were measured in situ over 3 months period to a depth of 30cm.Based on the measurement of CO2 concentrations in soil profile and soil tempreture and moisture.By analyzing the experimental data in detail,some results could be outlined as follows.Concentrations generally increased with depth.CO2 concentrations in soil profiles were about 10-20 times than those in atmosphere.The CO2 profiles in the soil of wheat fields under elevated and ambient CO2 and the bare land under ambient CO2 was investigated and some preliminary results were obtained. Within 0-30 cm in soil depth, CO2 in the pores of the upper soil layers vertically diffused upwards much more quickly than that in the lower soil layers. During the period with active wheat growth, elevated atmospheric CO2 by 200±40 μmol.mol-1 significantly increased the CO2 concentration in soil air within 0-30 cm in depth by 14%±5% (t-test, P < 0.001), which may lead to changes in soil physical and chemical properties. But further study is required to corroborate these changes.CO2 concentrations in soil air was closely relative to soil temperature and moisture,and it was variational with the wheat upgrowth.Not surprisingly, soil temperature was the major driver for soil CO2 concentrations,and it was noted to be a strong and positive predictor of soil CO2 concentrations.It can be explained as follows: Soil temperature strongly effect on the root and soil metabolic activity,accelerating soil microorganism respiration and root respiration ,so as to increase CO2 concentrations.Like other results reported in some review articles, soil moisture showed to a certain extent effect on the variability in soil CO2 concentrations. And their relationship showed positive correlation.The influence of moisture content on soil CO2 concentrations is complicated through its effect on respiratory activity of roots and microbes and on transport through the soil.Our studies show that the concentration gradient approach can yield a reasonable estimate of respiration rates under 34-41% soil water content. However, this method is not necessarily accurate and typically underestimates CO2 fluxes, and results showed that representative properties for the soils at the shallowest depth must be accurately determined to apply this method since the effective diffusion coefficient of CO2 is very sensitive to moisture content.