Barometric process separation: New method for quantifying nitrification, denitrification, and nitrous oxide sources in soils

A method (Barometric Process Separation, BaPS) was developed for the quanti fication of gross nitrification rates and denitrification rates in oxic soi l using intact soil cores incubated in an isothermal gas tight system. Gros s nitrification rates and denitrification rates are derived from measuremen ts of changes (i) in air pressure within the closed system, which are prima rily the result of the activities of nitrification (pressure decrease), den itrification (pressure increase), and respiration (pressure neutral), and ( ii) of O-2 and CO2 concentrations in the system. Besides these biological p rocesses, the contribution of physicochemical dissolution of produced CO2 i n soil water to the pressure changes observed is to be considered. The meth od allows collection of additional information shout the contribution of ni trification and denitrification to N2O emission from soil, provided simulta neous measurements of N2O emission are performed. Furthermore, BaPS can be used to quantify the percentage of N2O lost from nitrification, The advanta ge of BaPS is that disturbance of the soil system is minimized compared wit h other methods such as the use of gaseous inhibitors (e.g., acetylene) or application of N-15 compounds to the soil. We present the theoretical consi derations of BaPS, results for nitrification rates, denitrification rates, and identification of soil N2O sources in a well-aerated coniferous forest soil using BaPS. The suitability of BaPS as a method for determination of g ross nitrification is demonstrated by validation experiments using the N-15 -pool dilution technique.