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

Abstract

Background

The respiratory quotient, that is, the CO₂–O₂-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–¹⁵N method. Further, we aimed to elucidate whether RQ_AHR can be estimated from basic soil properties.

Results

Determined RQ_AHRs 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 (R² = 0.984) the measured RQ_AHRs. Applying the thus derived RQ_MLR to the calculation procedure led to good agreement between gross nitrification rates derived by the ¹⁵N 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 ¹⁵N pool dilution technique.