New aspects on the determination of soil‐specific respiration quotients of arable soils for the application in the barometric process separation technique

Background The respiratory quotient, that is, the CO 2 –O 2 ‐exchange ratio during aerobic heterotrophic soil respiration, (RQ AHR ) is one of the key variables of the barometric process separation (BaPS) technique. For reliable application, the BaPS method requires the adjustment of RQ AHR to soil‐specific substrate conditions. Aim The objective of the present study was to determine RQ AHR in five arable soils varying between pH 4 and 8 and carbon/nitrogen (C/N) ratios between 8.4 and 11.9 using the BaPS– 1 5 N method. Further, we aimed to elucidate whether RQ AHR can be estimated from basic soil properties. Results Determined RQ AHR s were soil specific and ranged between 0.74 and 1.53. RQ AHR particularly affected the calculation of gross nitrification rates but not soil respiration rates. Based on a multiple linear regression analysis, soil pH and the C/N ratio of the soil organic matter pool were identified to explain well ( R 2 = 0.984) the measured RQ AHR s. Applying the thus derived RQ MLR to the calculation procedure led to good agreement between gross nitrification rates derived by the 15 N pool dilution technique. Conclusions Future studies are needed to test whether this empirical relationship between RQ AHR , pH, and C/N ratio is generalizable. If this would be the case, the BaPS method could be applied without the use of a stable isotope and thus, being less resource demanding than the 15 N pool dilution technique.