Labile organic nitrogen transformations in clay and sandy-loam soils amended with 15 N-labelled faba bean and wheat residues

The results of this study suggest that mineralization of POMN is a major pathway through which mineral N is supplied in agricultural soils, with C/N ratio of crop residues and to a lesser extent soil properties, influencing the mineralization rate. Crow

Quantifying Nitrate Leaching under Commercial Red Raspberry Using Passive Capillary Wick Samplers

Groundwater NO–N contamination in the Abbotsford-Sumas Aquifer in British Columbia, Canada, has been attributed primarily to NO–N leaching from red raspberry ( L.); however, direct estimates of NO–N leaching are lacking. This study quantified the magnitude and timing of NO–N leaching under a commercial red raspberry field over 30 mo (October 2010–March 2013) using passive capillary wick samplers installed below the root zone at three row locations (irrigated row, nonirrigated row, and alley) after the critical period of field renovation and replanting. Substantial NO–N leaching (240 kg N ha) during the first year of monitoring was attributed to the effects of field renovation (including autumn chopping and incorporation of raspberry canes and soil fumigation and spring poultry broiler manure application) in the year prior to the initiation of monitoring. Lower NO–N leaching (80 kg N ha) occurred in the second year of monitoring under typical mineral fertilizer management practices. Strong seasonality of NO–N leaching was observed in both years, with ∼48% in autumn, 34% in spring and summer, and 17% in winter. Approximately 60% of the NO–N leaching was attributed to the alleys between raspberry rows, which did not receive mineral fertilizer or irrigation. The high proportion of leaching during spring and summer and from the alleys suggests that growing-season irrigation practices and alley vegetation management, respectively, would be good targets for the development of improved practices. The samplers were effective in quantifying the magnitude and timing of NO–N leaching from a commercial agricultural field and informing the development of improved practices

Seasonal changes in the abundance and activity of bacterial and fungal denitrifying communities associated with different compost amendments

Composts can be efficient organic amendments in potato culture as they can supply carbon and nutrients to the soil. However, more information is required to the effects of composts on denitrification and nitrous oxide emissions (N2O) and the emission-producing denitrifying communities. The effect of three compost amendments (municipal source separated organic waste compost (SSOC), forestry waste mixed with poultry manure compost (FPMC), and forestry residues compost (FRC)) on fungal and bacterial denitrifying communities and activity was examined in an agricultural field cropped to potatoes in during the fall, spring and summer seasons. The denitrification enzyme activity (DEA), N2O emissions and respiration were measured in parallel. N2O emission rates were greater in FRC-amended soils in the fall and summer, while soil respiration was highest in SSOC-amended soil in the fall. A large number of nirK denitrifying fungal transcripts was detected in the fall, coinciding with compost application while the greatest nirK bacterial transcripts were measured in the summer when plants were actively growing. Denitrifying community and transcript levels were poor predictors of DEA, N2O emissions or respiration rates in compost-amended soil. Overall, the sampling date was driving the population and activity levels of the three denitrifying communities under study.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Nitric Oxide Reductase Gene Expression and Nitrous Oxide Production in Nitrate-Grown Pseudomonas mandelii▿

Pure cultures of Pseudomonas mandelii were incubated with or without nitrate, which acts as a substrate and an electron acceptor for denitrification. Nitric oxide reductase (cnorB) gene expression was measured using a quantitative reverse transcription-PCR, and nitrous oxide emissions were measured by gas chromatography. P. mandelii cells in either the presence or absence of nitrate demonstrated an increase in cnorB gene expression during the first 3 h of growth. The level of expression of cnorB in nitrate-amended cells remained high (average, 2.06 × 108 transcripts/μg of RNA), while in untreated cells it decreased to an average of 3.63 × 106 transcripts/μg of RNA from 4 to 6 h. Nitrous oxide accumulation in the headspace was detected at 2 h, and cumulative emissions continued to increase over a 24-h period to 101 μmol in nitrate-amended cells. P. mandelii cnorB gene expression was not detected under aerobic conditions. These results demonstrate that P. mandelii cnorB gene expression was induced 203-fold at 4 h when nitrate was present in the medium. Accumulations of N2O indicated that the cNorB enzyme was synthesized and active

Analysis of Four Delineation Methods to Identify Potential Management Zones in a Commercial Potato Field in Eastern Canada

Management zones (MZs) are delineated areas within an agricultural field with relatively homogenous soil properties, and therefore similar crop fertility requirements. Consequently, such MZs can often be used for site-specific management of crop production inputs. This study evaluated the effectiveness of four classification methods for delineating MZs in an 8-ha commercial potato field located in Prince Edward Island, Canada. The apparent electrical conductivity (ECa) at two depths from a commercial Veris sensor were used to delineate MZs using three classification methods without spatial constraints (i.e., fuzzy k-means, ISODATA and hierarchical) and one with spatial constraints (i.e., spatial segmentation method). Soil samples (0.0–0.15 m depth) from 104 sampling points was used to measure soil physical and chemical properties and their spatial variation in the field were used as reference data to evaluate four delineation methods. Significant Pearson correlations between ECa and soil properties were obtained (0.22 < r < 0.85). The variance reduction indicated that two to three MZs were optimal for representing the field’s spatial variability of soil properties. For two MZs, most soil physical and chemical properties differed significantly between MZs for all four delineation methods. For three MZs, there was greater discrimination among MZs for several soil properties for the spatial segmentation-based method compared with other delineation methods. Moreover, consideration of the spatial coordinates of the data improved the delineation of MZs and thereby increased the number of significant differences among MZs for individual soil properties. Therefore, the spatial segmentation method had the greatest efficiency in delineation of MZs from statistical and agronomic perspectives

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

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

Effect of pH and Temperature on Denitrification Gene Expression and Activity in Pseudomonas mandelii▿

Pseudomonas mandelii liquid cultures were studied to determine the effect of pH and temperature on denitrification gene expression, which was quantified by quantitative reverse transcription-PCR. Denitrification was measured by the accumulation of nitrous oxide (N2O) in the headspace in the presence of acetylene. Levels of gene expression of nirS and cnorB at pH 5 were 539-fold and 6,190-fold lower, respectively, than the levels of gene expression for cells grown at pH 6, 7, and 8 between 4 h and 8 h. Cumulative denitrification levels were 28 μmol, 63 μmol, and 22 μmol at pH 6, 7, and 8, respectively, at 8 h, whereas negligible denitrification was measured at pH 5. P. mandelii cells grown at 20°C and 30°C exhibited 9-fold and 94-fold increases in levels of cnorB expression between 0 h and 2 h, respectively, and an average 17-fold increase in levels of nirS gene expression. In contrast, induction of cnorB and nirS gene expression for P. mandelii cells grown at 10°C did not occur in the first 4 h. Levels of cumulative denitrification at 10 h were 6.6 μmol for P. mandelii cells grown at 10°C and 20°C and 30 μmol for cells grown at 30°C. Overall, levels of cnorB and nirS expression were relatively insensitive to pH values over the range of pH 6 to 8 but were substantially reduced at pH 5, whereas gene expression was sensitive to temperature, with induction and time to achieve maximum gene expression delayed as the temperature decreased from 30°C. Low pH and temperature negatively affected denitrification activity