Effects of nitrate concentration on the denitrification potential of a calcic cambisol and its fractions of N2, N2O and NO

The direct measurement of denitrification dynamics and its product fractions is important for parameterizing process-oriented model(s) for nitrogen cycling in various soils. The aims of this study are to a) directly measure the denitrification potential and the fractions of nitrogenous gases as products of the process in laboratory, b) investigate the effects of the nitrate (NO (3) (-) ) concentration on emissions of denitrification gases, and c) test the hypothesis that denitrification can be a major pathway of nitrous oxide (N2O) and nitric oxide (NO) production in calcic cambisols under conditions of simultaneously sufficient supplies of carbon and nitrogen substrates and anaerobiosis as to be found to occur commonly in agricultural lands. Using the helium atmosphere (with or without oxygen) gas-flow-soil-core technique in laboratory, we directly measured the denitrification potential of a silt clay calcic cambisol and the production of nitrogen gas (N-2), N2O and NO during denitrification under the conditions of seven levels of NO (3) (-) concentrations (ranging from 10 to 250 mg N kg(-1) dry soil) and an almost constant initial dissolved organic carbon concentration (300 mg C kg(-1) dry soil). Almost all the soil NO (3) (-) was consumed during anaerobic incubation, with 80-88 % of the consumed NO (3) (-) recovered by measuring nitrogenous gases. The results showed that the increases in initial NO (3) (-) concentrations significantly enhanced the denitrification potential and the emissions of N-2 and N2O as products of this process. Despite the wide range of initial NO (3) (-) concentrations, the ratios of N-2, N2O and NO products to denitrification potential showed much narrower ranges of 51-78 % for N-2, 14-36 % for N2O and 5-22 % for NO. These results well support the above hypothesis and provide some parameters for simulating effects of variable soil NO (3) (-) concentrations on denitrification process as needed for biogeochemical models.