Effect of three nitrogen fertilizer sources on denitrification rate under irrigated potato production on sandy soils

Large inputs of nitrogen (N) are required to optimize yield and quality of potato (Solanum tuberosum L.), and it may result in a high potential for N losses including denitrification. This 5 yr study compared the effect of three N fertilizer sources [ammonium nitrate (AN), ammonium sulfate (AS), and polymer-coated urea (PCU)] at 200 kg N ha−1 (N200) and an unfertilized control (N0) on denitrification rate (DR) from irrigated potato production on a coarse-textured soil in eastern Canada. Fertilizer was banded all at-planting (PCU) or split 40% at-planting and 60% at-hilling (AN and AS). The DR was measured biweekly from planting to harvest at two locations (ridge and furrow) using the acetylene blockage technique. The mean annual DR, averaged across N treatments, ranged from 0.8 to 8.0 μg N2O-N kg dry soil−1 d−1, and it was most closely related to the water inputs in the 72 h before DR measurements. Mean DR averaged across year was greater for N200 than for N0 (4.2 vs. 3.4 μg N2O-N kg dry soil−1 d−1) but did not differ among N sources. Our results suggest that choice of N fertilizer source in sandy soils is more important in controlling losses of N by leaching than by denitrification.

Effect of Nitrate and Acetylene on nirS, cnorB, and nosZ Expression and Denitrification Activity in Pseudomonas mandelii

ABSTRACT Nitrate acts as an electron acceptor in the denitrification process. The effect of nitrate in the range of 0 to 1,000 mg/liter on Pseudomonas mandelii nirS, cnorB, and nosZ gene expression was studied, using quantitative reverse transcription-quantitative PCR. Denitrification activity was measured by using the acetylene blockage method and gas chromatography. The effect of acetylene on gene expression was assessed by comparing denitrification gene expression in P. mandelii culture grown in the presence or absence of acetylene. The higher the amount of NO3 − present, the greater the induction and the longer the denitrification genes remained expressed. nirS gene expression reached a maximum at 2, 4, 4, and 6 h in cultures grown in the presence of 0, 10, 100, and 1,000 mg of KNO3/liter, respectively, while induction of nirS gene ranged from 12- to 225-fold compared to time zero. cnorB gene expression also followed a similar trend. nosZ gene expression did not respond to NO3 − treatment under the conditions tested. Acetylene decreased nosZ gene expression but did not affect nirS or cnorB gene expression. These results showed that nirS and cnorB responded to nitrate concentrations; however, significant denitrification activity was only observed in culture with 1,000 mg of KNO3/liter, indicating that there was no relationship between gene expression and denitrification activity under the conditions tested.

Ralstonia basilensisM91-3, a denitrifying soil bacterium capable of usings-triazines as nitrogen sources

The purpose of this study was to characterize the phylogenetic and phenotypic traits of M91-3, a soil bacterium capable of mineralizing atrazine (2-chloro-4-N-isopropyl-6-N-ethyl-s-triazine). The isolate was identified as Ralstonia basilensis based on 99.5% homology of the 16S rRNA sequence and various chemotaxonomic data. The isolate used atrazine as the sole source of energy, carbon, and nitrogen. It could also use several other s-triazines as nitrogen sources. Ralstonia basilensis M91-3 was capable of denitrification, which was confirmed by gas chromatographic analysis of nitrous oxide under acetylene blockage conditions.Key words: atrazine biodegradation, denitrification, herbicide degrader, Ralstonia basilensis, triazine degradation.

Kinetic Parameters of Denitrification in a River Continuum

ABSTRACT Kinetic parameters for nitrate reduction in intact sediment cores were investigated by using the acetylene blockage method at five sites along the Swale-Ouse river system in northeastern England, including a highly polluted tributary, R. Wiske. The denitrification rate in sediment containing added nitrate exhibited a Michaelis-Menten-type curve. The concentration of nitrate for half-maximal activity (Kmap ) by denitrifying bacteria increased on passing downstream from 13.1 to 90.4 μM in the main river, but it was highest (640 μM) in the Wiske. The apparent maximal rate (Vmaxap ) ranged between 35.8 and 324 μmol of N m−2 h−1 in the Swale-Ouse (increasing upstream to downstream), but it was highest in the Wiske (1,194 μmol N m−2 h−1). A study of nitrous oxide (N2O) production at the same time showed that rates ranged from below the detection limit (0.05 μmol of N2O-N m−2 h−1) at the headwater site to 27 μmol of N2O-N m−2 h−1 at the downstream site. In the Wiske the rate was up to 570 μmol of N2O-N m−2 h−1, accounting for up to 80% of total N gas production.