Studies On Maize Soil Respiration In Taiyuan Basin And Its Relation With Environmental Factors

Using an infrared gas analyser (IRGA) attaching a 6400-09 chamber, soil-surface CO₂ efflux and its seasonal and diurnal variation were measured in a maize cultivated-land located in Shanxi Academy of Agricultural Sciences. The measurements were made from January to December 2005 in an interval of 1-5 times a month and 33 measurements were examined for whole year. Soil temperature over 0-10cm depth was measured with the temperature probe attaching to IRGA and the soil water content at the sampling location was measured by a TDR (TDR300, spectrum technologies.inc.) and an oven method at 105℃. The physical and chemical properties of the soil were also measured.It was found that the seasonal change of soil respiration in the maize land was significant and that its trend followed the changes of soil temperature: lower in the winter and the spring and higher in the middle summer and the beginning of autumn. The soil respiration showed aminimum of about 0.5μmolCO₂m^-2 s^-1 in January and February when the soil temperature was near 0℃;from March to the middle of May the soil respiration increased slowly to about 2 μmolCO₂ m^-2 s^-1 though the temperature at the same period had a big increase reaching more than 20 ℃;at the end of May the soil respiration rate reached to 5 μmolCO₂ m^-2 s^-1;between July and September the respiration rate fluctuated in 4-12μmolCO₂ m^-2 s^-1 depending on weather condition, mostly on raining or irrigation of maize field;then the soil temperature decreased and the respiration rate lowed to another minimum value of 0.5μmolCO₂ m^-2 s^-1. The weighted monthly mean value of soil respiration in maize field from January to December was 0.75, 0.36, 0.74, 1.64, 5.26, 5.19, 5.08, 11.00, 5.40, 5.65, 4.66, 1.91μmolCO₂ m^-2 s^-1, respectively, and annual mean value from January to December was 3.97 ± 3.06μmolCO₂ m^-2 s^-1;6.26± 2.33μmolCO₂ m^-2 s^-1 from May to October. Gaussian distribution of 3 parameters could describe the daily change of soil respiration with theday of the year.The relationship between soil respiration and soil temperature over 10cm depth can be described by linear, exponential or Lloyd & Taylor equation. The soil temperature explained 30% and 41% of temporal variation of soil respiration, respectively, using all data and the data excluding water stressed in exponential function, and 33% and 41, respectively, in Lloyd & Taylor function. Qiowas about 2.3 and R10 was 2.3and2.7umolCO2m"V1.Followed the temperature, soil water content was second factor controlling soil respiration. The correlation coefficient between soil respiration and soil water content increased from 0.30 to 0.39 when the soil respiration was normalized to 10 °C. The model including both temperature and soil water content explained more than 50% of the variation in soil efflux.Soil respiration rate showed an asymmetric diurnal pattern, with the minimum appearing around earlier morning and the maximum around earlier afternoon. Mean value of soil respiration on July 22, August 4 and October 10 was 2.77±0.13, 6.72±0.25, 6.05±0.40umol CO2 mV, respectively. The correlation between the diurnal changes of soil respiration and soil temperature was significant on August, but not on June and on October. Annual soil CO2 emission from the soil was about 1477 gCm"2 in 2005.