Determination of upland soil respiration and its components with BaPS System

A BaPS (Barometric Process Separation) system was introduced to determine the seasonal variation of soil respiration rate in the soybean and maize fields. CO_2 concentration in headspace of the BaPS was simultaneously detected by a gas chromatograph (GC/Agilent4890D). Root biomass of soybean and maize was measured while determining the soil respiration rate. Results indicated that the soil respiration rate measured by the BaPS was comparable to that determined by the gas chromatograph.An obvious seasonal variation of soil respiration rate in the rhizosphere depending on root biomass was found, while that in the non-rhizosphere was not pronounced. Seasonal soil respiration rate in the rhizosphere averaged 29.8±6.4mg·kg -1·d -1 (in C) and 70.8±38.6mg·kg -1·d -1(in C) for the soybean and maize fields, respectively. In contrast, the soil respiration rate was relatively lower in the non-rhizosphere, with the seasonal average of 14.4±5.1mg·kg -1·d -1(in C)for the soybean field and 18.1±8.7mg·kg -1·d -1(in C)for the maize field. We defined the difference of soil respiration rates in the rhizosphere and in the non-rhizosphere as root-derived respiration, and found that the root-derived respiration accounted for 50% and 69% of the total soil respiration in the soybean and maize fields, respectively. A significant linear relationship between the root-derived respiration rate and root biomass produced a concept of root respiration coefficient, which was estimated to be 0.048mg·mg -1·d -1 for the soybean and 0.042mg·mg -1·d -1 for the maize field, respectively.