Nitrate stability in loess soils under anaerobic conditions - laboratory studies

The objective of this laboratory study with six loess soils (three Eutric Cambisols and three Haplic Phaeozems) incubated under flooded conditions was to examine the effect of a wide range of NO3- doses under anaerobic conditions on soil redox potential and N2O emission or absorption. Due to the fact that loess soils are usually well-drained and are expected to be absorbers during prevailing part of the season, the study aimed at determination of the conditions decisive for the transition from emission to absorption process. On the basis of the response to soil nitrate level, the two groups of soils we're distinguished with high and low denitrification capacity. The soil denitrification activity showed Michaelis-Menten kinetics with respect to soil nitrate content with K-M in the range 50-100 mg NO3--N kg(-1). Percentage of nitrates converted to N2O increased linearly with nitrate concentration in the range from 25 to 100 mg NO3--N kg(-1) up to 43% and decreased linearly at higher concentrations reaching practically zero at concentrations about 600 mg NO3--N kg(-1). No denitrification was observed below 25 mg NO3--N kg(-1). Nitrous oxide absorption in soil occurred only at nitrate concentrations to 100 mg NO3--N kg(-1) and in this concentration range was proportional to the denitrification rate. Nitrous oxide was formed at redox potentials below +200 mV and started to disappear at negative E-h values.