In the majority of agricultural soils, ammonium (NH +) is rapidly converted to nitrate (NO 3-) in the biological ammonia and nitrite oxidation processes known as nitrification. The often rate-limiting step of ammonia oxidation to nitrite is mediated by ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The response of AOA and AOB communities to organic and conventional nitrogen (N) fertilizers, and their relative contributions to the nitrification process were examined for an agricultural silage corn system using a randomized block design with 4 N treatments: control (no additional N), ammonium sulfate (AS) fertilizer at 100 and 200 kg N ha-1 , and steer-waste compost (200 kg total N ha-1) over four seasons. DNA was extracted from the soil, and real-time PCR and 454-pyrosequencing were used to evaluate the quantity and diversity of the amoA gene which encodes subunit A of ammonia monooxygenase. Soil pH, nitrate pools, and nitrification potentials were influenced by ammonium and organic fertilizers after the first fertilization, while changes in AOB abundance and community structure were not apparent until after the second fertilization or later. The abundance of AOA was always greater than AOB but was unaffected by N treatments. In contrast, AOB abundance and community structure were changed significantly by ammonium fertilizers. Specific inhibitors of nitrification were used to evaluate the relative contribution of AOA and AOB to nitrification. We found that AOB dominantly contributed to potential nitrification activity determined at 1 mM ammonium in soil slurries and nitrification potential activity was higher in soils treated with ammonium fertilizers relative to control soils. However, AOA dominated gross nitrification activity in moist soils. Our result suggests that AOB activity and community are more responsive to ammonium fertilizers than AOA but that in situ nitrification rate is controlled by ammonium availability in this agricultural soil. Understanding this response of AOA and AOB to N fertilizers may contribute to improving strategies for the management of nitrate production in agricultural soils.

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Measurements of gross N transformation rates are important to properly understand N cycling processes in agricultural soils where both productive and consumptive processes occur. The objective of the study was to determine the effect of repeated application of dairy‐waste compost (DC), liquid dairy‐waste (LW), and ammonium sulfate (AS) on gross N mineralization and nitrification rates and N supplying potential of an agricultural soil. Our goal was to examine both production and consumption of inorganic N for their effects on the balance between N supply from treated dairy‐wastes and plant N demand. Treatments were applied at rates approximately equivalent to 100 and 200 kg available N ha−1 for 6 yr annually. Field‐based N15 pool dilution techniques and laboratory incubation experiments were employed to measure gross rates and mineralization potential of the soil. Both levels of DC raised the labile organic N pool significantly but only the high level DC significantly increased the decomposition rate constant (k). The mean gross N mineralization rates for 1999 to 2002 for the high levels of DC, LW, and AS were 5.72, 2.89, and 1.27 mg N kg−1 d−1, whereas gross nitrification rates were 10.24, 1.57, and 0.74 mg N kg−1 d−1, respectively. Net mineralization rates were <35% of gross rates while nitrate consumption was not significant under any treatment. Variability in gross rates was high in the soils receiving DC, which could be due to presence of hotspots of labile organic matter. Elevated gross N transformation rates in plots receiving DC indicate the dynamic nature of this agricultural soil after repeated applications of dairy‐waste.

An agricultural soil was treated with dairy-waste compost, ammonium-sulfate fertilizer or no added nitrogen (control) and planted to silage corn for 6 years. The kinetics of nitrification were determined in laboratory-shaken slurry assays with a range of substrate concentrations (0-20 mM NH(4)(+)) over a 24-h period for soils from the three treatments. Determined concentrations of substrate and product were fit to Michaelis-Menten and Haldane models. For all the treatments, the Haldane model was a better fit, suggesting that significant nitrification inhibition may occur in soils under high ammonium conditions similar to those found immediately after fertilization or waste applications. The maximum rate of nitrification (V(max)) was significantly higher for the fertilized and compost-treated soils (1.74 and 1.50 mmol N kg(-1) soil day(-1)) vs. control soil (0.98 mmol kg(-1) soil day(-1)). The K(m) and K(i) values were not significantly different, with average values of 0.02 and 27 mM NH(4)(+), respectively. Our results suggest that both N sources increased nitrifier community size, but did not shift the nitrifier community structure in ways that influenced enzyme affinity or sensitivity to ammonium. The K(m) values are comparable to those determined directly in other soils, but are substantially lower than those from most pure cultures of ammonia-oxidizing bacteria.

Improved understanding of the effects of dairy‐waste treatment and land application on microbial processes and products is required to predict the outcome of waste applications and avoid undesirable environmental impacts. Our objective was to assess effects of treated dairy‐waste on soil N pools, nitrification, plant N availability, and yield in a silage cornfield (Zea mays L.) treated with ammonium sulfate (AS), dairy‐waste compost (DC), or liquid dairy‐waste (LW) as N sources at two levels of application over 5 yr. Increases in soil C and N, nitrate, and available P and K were observed for the DC treated soils throughout the 5‐yr period. Soil organic C increases for the high‐level DC treated soil doubled the C pool resulting in an increase of 14 Mg C ha−1 The highest nitrate accumulation was at the 60‐ to 90‐cm depth for soils receiving high level of DC (200 kg N ha−1), which moved to lower depths in subsequent years. Soils receiving a high‐level of DC or LW showed a three‐fold increase in nitrifier activity compared with the control. There was a positive silage corn yield response with all the treatments, with DC having the highest yields. While N from AS and LW are available for plant uptake almost immediately, the organic N in compost continued to mineralize throughout the growing season, after harvest and in subsequent years. Careful management of application rates to optimize the timing of N release versus plant demand and of post‐harvest nutrient pools are suggested for the prevention of excessive nitrate accumulations and movement from repeated dairy‐waste applications.

This study confirms the significant impact of septic systems on faecal pollution during baseflow and provides the tools that will enable effective pollution monitoring at the watershed scale.

We have demonstrated in our earlier work that a few natural and synthetic estrogens can be effectively transformed through reactions mediated by lignin peroxidase (LiP). The behaviors of such reactions are variously influenced by the presence of natural organic matter (NOM) and/or veratryl alcohol (VA). Certain white rot fungi, e.g. Phanerochaete chrysosporium, produce VA as a secondary metabolite along with LiP in nature where NOM is ubiquitously present. Herein, we report a study on the products resulting from LiP-mediated oxidative coupling reactions of a representative estrogen, 17beta-estradiol (E2), and how the presence of NOM and/or VA impacts the formation and distribution of the products. A total of six products were found, and the major products appeared to be oligomers resulting from E2 coupling. Our experiments revealed that these products likely formed colloidal solids in water that can be removed via ultrafiltration or settled during ultracentrifugation. Such a colloidal nature of the products could have important implications in their treatability and environmental transport. In the presence of VA, the products tended to shift toward higher-degree of oligomers. When NOM was included in the reaction system, cross-coupling between E2 and NOM appeared to occur. Data obtained from E-SCREEN test confirmed that the estrogenicity of E2 can be effectively eliminated following sequential reactions mediated by LiP.