Denitrification in arable soils in relation to their physico-chemical properties and fertilization practice

Increased use of N-fertilizers in the Czech Republic in recent decades has been accompanied by increased amounts of N compounds in the general environment, and also by shifts in the rates of biological N-processes in agricultural soils. Knowledge of these changes, including rates, distribution and variability of denitrification in soils in the Czech Republic is, however, very limited. In the period 1993-1995, potential denitrification (i.e. denitrifying enzyme activity (DEA) and denitrification potential (DP)), was determined at 13 different sites, in soils with differing physico-chemical and biological properties, but which were typical of large areas in the Czech Republic. In 1994-1995, more detailed research on four differently fertilized plots of a sandy-loam cambisol was conducted on nine occasions in order to analyze seasonal effects and to establish if more than 20 yr of fertilization and selected environmental factors had influenced denitrification. This research was completed in 1996, when 12 differently fertilized plots of the same soil were examined. When a range of soils was investigated, DEA reached values between 15 and 680 ng N(2)O-N g(-1) h(-1), corresponding roughly to 1.3-16 mg N kg(-1) d(-1), and DP reached values between 6.6-52 mg N kg(-1) d(-1). No significant relationship was found between DEA and DP, indicating the independence of the existing metabolic activity of the denitrifier community (DEA) and its potential for rapid development if the environmental conditions change in its favor (DP). While DEA did not correlate with any of the measured soil properties, DP correlated highly significantly with soil pH (H2O) and organic carbon content. Detailed research on a sandy loam cambisol showed (i) a large temporal variability of DEA and DP, (ii) an influence of long-term fertilization on denitrification characteristics; DEA and DP responded differently: while DEA increased with all fertilization rates. DP increased in moderately fertilized soils, but decreased significantly in a highly fertilized soil and (iii) a positive correlation of DP with many soil properties, including pH, microbial biomass and dehydrogenase activity.