Effect of ammonium-, nitrite- and nitrate nitrogen on anaerobic nitrogenase activity in soil

Sandy loam soil, with added glucose, was incubated anaerobically under N₂ and subjected to repeated 1-h C₂H₂ reduction assays. In the presence of 1% glucose the addition of 50 μg NH₄⁺ ?N/g or of 20 μg NO^?₃ N/g (untreated soil contained 1.2 μg NH⁺₄?N and 7.10 μg NO^?₃-N/g) caused at least some suppression of nitrogenase activity. Activity developed when the KCl-extractable soil inorganic nitrogen concentration dropped below 35 μg/g. In the presence of 0.1 or 0.05% glucose the addition of 5 μg NH⁺₄?N/g caused some suppression of nitrogenase activity. However, activity developed when the soil NH₄⁺-N concentration dropped below about 4 μg/g. With 0.1% glucose and 5 μg added NO^?₂ N/g, activity did not develop until the soil NO^?₂ -N concentration dropped to zero. Added NO^?₃ N was rapidly reduced and denitrified to NO^?₂- N, N₂O-N and NH⁺₄ N and furthermore caused some inhibition of CO₂ evolution. The data from NH₄^?-addition experiments are consistent with a nitrogenase repression/ derepression threshold of 4 and 35μg NH⁺₄-N/g at 0.05 and 1% glucose concentrations, respectively. The data from NO^?₂- and NO^?₃-addition experiments suggest a combination of repression and toxicity effects in the presence of added NO^?₃ N.     

Nitrate Transformation and N2O Emission in a Typical Intensively Managed Calcareous Fluvaquent Soil: A 15-Nitrogen Tracer Incubation Study

A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO₃-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N₂O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO₃-N decreased. When ¹⁵NO₃-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg^?1 only 1.1 ± 0.4 mg kg^?1 NO₃-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly (P < 0.05) with increasing amount of straw. Total N₂O-N emissions were at levels of only micrograms kg^?1 soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N₂O.     

The influence of glucose and nitrate concentrations upon denitrification rates in sandy soils

Dentrification rates in two soils were assessed separately as a function of NO₃^? concentration while providing a constant initial glucose concentration, and as a function of glucose concentration while providing a constant initial NO₃^?-N concentration. Of the soils used, a Hanford sandy loam and a Coachella fine sand, the bacteria in the former produced higher rates of denitrification with a maximum loss of 1500 μg NO₃^?-N/ml day^?1 as compared to a loss of 150 μg NO₃^?-N/ml day^?1 from the latter. Rates of loss closely approximated Michaelis Menten kinetics in the Coachella sand, and K_m values for glucose-C and NO₃^?-N were 500 μg/ml and 170 μg/ml, respectively. Rates of loss of NO₃^?-N from the Hanford soil did not approximate Michaelis-Menten kinetics, and this was attributed to failure to saturate enzyme systems in the denitrifying bacteria with glucose and nitrogen when each was held constant. C/N ratios around 2 appeared to provide the greatest rates of denitrification. High C/N ratios or high glucose concentrations (1.8 per cent) retarded denitrification, with fungal growth and a subsequent drop in pH occuring. A Pseudomonas was incubated aerobically for 24 h followed by a 72 h anaerobic incubation with nitrate as the sole nitrogen source at 0, 10, 50, 100, 250 and 500mg N/ml concentrations. Assimilatory nitrate reduction never exceeded 75 mg N/ml, and it was concluded that this mode of nitrate reduction is insignificant at higher nitrate concentrations by comparison to dissimilatory nitrate reduction, i.e. denitrification.     

Denitrification enzyme activity and potential of subsoils under grazed grasslands assayed by membrane inlet mass spectrometer

The importance of subsoil denitrification on the fate of agriculturally derived nitrate (NO₃) leached to groundwater is crucial for budgeting N in an ecosystem and for identifying areas where the risk of excess NO₃ is reduced. However, the high atmospheric background of di-nitrogen (N₂) causes difficulties in assessing denitrification enzyme activity (DEA) and denitrification potential (DP) in soils directly. Here, we apply Membrane Inlet Mass Spectrometry (MIMS) technique to investigate indirectly DEA and DP in soils by measuring N₂/Ar ratio changes in headspace water over soil. Soils were collected from 0-10, 15-25 and 60-70 cm depths of a grazed ryegrass and grass-clover. The samples were amended with helium-flushed deionized water containing ranges of NO₃ and carbon (glucose-C) and were incubated for six hours in the dark at 21 °C. The peaks for N₂/Ar ratio, declined with increasing soil depth, indicating a reduced substrate requirements to initiate DEA en-masse (15-30 mg NO₃-N alone or with 60-120 mg glucose-C, kg⁻¹ soil). The dissolved N₂O concentrations were very small (0.004-0.269 μg N kg⁻¹ soil) but responded well to the added N and C, showing a reduction in DEA with soil depth. In three separate studies, only subsoils were incubated for 3 days at 12 °C with 20-30 mg NO₃-N ± 40-60 mg glucose-C, kg⁻¹ soil. Denitrification capacity (DC, NO₃ only treatment) was not statistically different to the control (no amendment) within a land use (0.03-0.05 vs. 0.07-0.22 mg N kg⁻¹ soil d⁻¹), the highest being in ryegrass subsoils receiving groundwater. The DP was significantly (P < 0.0001) higher in subsoils under ryegrass than under grass-clover (0.50-0.71 vs. 1.15 mg N kg⁻¹ soil d⁻¹). The rates of DP (NO₃ + glucose-C) increased significantly (P < 0.0001) in unsaturated and saturated subsoils (0.92 and 2.19 mg N kg⁻¹ soil d⁻¹, respectively) of grass-clover, due to the higher reductive state resulting from the 10 day pre-incubation. Available C accelerated denitrification in soils and superseded the temporary elevation in oxidative state due to NO₃ addition. The substrates load differences between the land uses regulated the degree of denitrification rates. Results suggest that both dissolved N₂O measured by gas chromatography and N₂/Ar ratio measured by MIMS to indirectly determine DEA, and the latter to quantify total DC/DP in soils can be used. However, interference of oxygen in the MIMS system should be considered if available C is added or is naturally elevated in soil or groundwater.     

Acetylene and N-serve effects upon N2O emissions from NH4+ and NO3− treated soils under aerobic and anaerobic conditions

N₂O emissions from soils treated with NH₄⁺-N under aerobic conditions in the laboratory were 3- to 4-fold higher than those from controls (no extra N added) or when NO₃^?-N was added. Although the emission of N₂O-N in these field and laboratory experiments represented only 0.1–0.8% of the applied fertilizer NH₄⁺-N and are therefore not significant from an agronomic standpoint, these studies have conclusively demonstrated that the oxidation of applied ammoniacal fertilizers (nitrification) could contribute significantly to the stratospheric N₂O pool.Like N-serve, acetylene was shown to be a potent inhibitor of nitrification as it stopped the oxidation of NH₄⁺-N to (NO₃⁺-N + NO₂^?)-N and hence reduced the evolution of N₂O from nitrification within 60 min after its addition.Although high amounts of NO₃^?-N were present, the rate of denitrification was very low from soils with moisture up to 60% saturation. The further increase in the degree of saturation resulted in several-fold increase of denitrification which eventually became the predominant mechanism of gaseous N losses under anaerobic conditions.     

不同碳源添加对钙质土高累积硝态氮向土壤有机氮库转化的研究

Excessive amounts of nitrate have accumulated in many soils on the North China Plain due to the large amounts of chemical N fertilizers or manures used in combination with low carbon inputs. We investigated the potential of different carbon substrates added to transform soil nitrate into soil organic N (SON). A 56-d laboratory incubation experiment using the 15 N tracer (K15 NO3 ) technique was carried out to elucidate the proportion of SON derived from accumulated soil nitrate following amendment with glucose or maize straw at controlled soil temperature and moisture. The dynamics and isotopic abundance of mineral N (NO3 and NH+4 ) and SON and greenhouse gas (N2O and CO2 ) emissions during the incubation were investigated. Although carbon amendments markedly stimulated transformation of nitrate to newly formed SON, this was only a substitution effect of the newly formed SON with native SON because SON at the end of the incubation period was not significantly different (P > 0.05) from that in control soil without added C. At the end of the incubation period, amendment with glucose, a readily available C source, increased nitrate immobilization by 2.65 times and total N2O-N emission by 33.7 times, as compared with maize straw amendment. Moreover, the differences in SON and total N2O-N emission between the treatments with glucose and maize straw were significant (P < 0.05). However, the total N2O-N emission in the straw treatment was not significantly (P > 0.05) greater than that in the control. Straw amendment may be a potential option in agricultural practice for transformation of nitrate N to SON and minimization of N2O emitted as well as restriction of NO3-N leaching.     

Formation of carcinogenic nitrosamines in soils

The possible formation of carcinogenic nitrosamines in soils was examined. Soil samples amended with NO₂^?-N and dimethylamine incubated for 30 days and analysed every 3 days, showed increasing amounts of dimethylnitrosamine up to 12–15 days. The concentration reached as high as 6.5 parts/10⁶, thereafter, a decline was noted. Most of the nitrosamines disappeared in soils after 30 days. Addition of inorganic N reduced the decomposition of dimethylamine. Soil incubation studies with NO₂^? and trimethylamine showed about 80% reduction in the amount of nitrosamines formed as compared to dimethylamine. Analysis of soil samples from fertilized and polluted areas showed significant amounts of NO^?₃-N but no nitrosamines. Application of 10 parts/10⁶ of dimethylamine to these soil samples resulted in the formation of 0.10 to 0.50 parts/10⁶ of nitrosamines. Autoclaved soil samples incubated with NO₂^? and dimethylamine for 12–15 days produced small amounts of nitrosamines. Addition of glucose to soil samples increased the amounts of nitrosamines formed.     

Effects of carbon and phosphorus addition on microbial respiration,N<Subscript>2</Subscript>O emission,and gross nitrogen mineralization in a phosphorus-limited grassland soil

Soil microbes are frequently limited by carbon (C), but also have a high phosphorus (P) requirement. Little is known about the effect of P availability relative to the availability of C on soil microbial activity. In two separate experiments, we assessed the effect of P addition (20 mg P kg^?1 soil) with and without glucose addition (500 mg C kg^?1 soil) on gross nitrogen (N) mineralization (¹⁵N pool dilution method), microbial respiration, and nitrous oxide (N₂O) emission in a grassland soil. In the first experiment, soils were incubated for 13 days at 90% water holding capacity (WHC) with addition of NO₃^? (99 mg N kg^?1 soil) to support denitrification. Addition of C and P had no effect on gross N mineralization. Initially, N₂O emission significantly increased with glucose, but it decreased at later stages of the incubation, suggesting a shift from C to NO₃^? limitation of denitrifiers. P addition increased the N₂O/CO₂ ratio without glucose but decreased it with glucose addition. Furthermore, the ¹⁵N recovery was lowest with glucose and without P addition, suggesting a glucose by P interaction on the denitrifying community. In the second experiment, soils were incubated for 2 days at 75% WHC without N addition. Glucose addition increased soil ¹⁵N recovery, but had no effect on gross N mineralization. Possibly, glucose addition increased short-term microbial N immobilization, thereby reducing N-substrates for nitrification and denitrification under more aerobic conditions. Our results indicate that both C and P affect N transformations in this grassland soil.     

Greenhouse gas emissions and nutrient supply rates in soil amended with biofuel production by-products

Ethanol production results in distiller grain, and biodiesel produces glycerol as by-product. However, there is limited information on effects of their addition on evolution of N₂O and CO₂ from soils, yet it is important to enable our understanding of impacts of biofuel production on greenhouse gas budgets. The objective of this study was to evaluate the direct effects of adding wet distillers grain (WDG), thin stillage (TS), and glycerol at three rates on greenhouse gas emissions (N₂O and CO₂) and nutrient supply rates in a cultivated soil from the Canadian prairies. The WDG and TS application rates were: 100, 200, or 400 kg N ha^?1, whereas glycerol was applied at: 40, 400, or 4,000 kg C ha^?1 applied alone (G???N) or in a combination with 300 kg N ha^?1 (G?+?N). In addition, conventional amendments of urea (UR) and dehydrated alfalfa (DA) were added at the same rates of total N as the by-products for comparative purposes. The production of N₂O and CO₂ was measured over an incubation period of 10 days in incubation chambers and Plant Root Simulator? resin membrane probes were used to measure nutrient (NH ₄ ⁺ -N, NO ₃ ^? -N, and PO ₄ ^?3 -P) supply rates in the soil during incubation. Per unit of N added, urea tended to result in the greatest N₂O production, followed by wet distillers grain and thin stillage, with glycerol and dehydrated alfalfa resulting in the lowest N₂O production. Cumulative N₂O production increased with increasing the rate of N-containing amendments and was the highest at the high rate of UR treatment. Addition of urea with glycerol contributed to a higher rate of N₂O emission, especially at the low rate of glycerol. The DA and WDG resulted in the greatest evolution of CO₂ from the soil, with the thin stillage resulting in less CO₂ evolved per unit of N added. Addition of N fertilizer along with glycerol enhanced microbial activity and decomposition. The amendments had significant impacts on release of available nutrient, with the UR treatments providing the highest NO ₃ ^? -N supply rate. The TS treatments supplied the highest rate of NH ₄ ⁺ -N, followed by WDG compared to the other amendments. The WDG treatments were able to provide the greatest supply of PO ₄ ^?3 -P supply in comparison to the other amendments. Microbial N immobilization was associated with glycerol treatments applied alone. This study showed that the investigated biofuel by-products can be suitable soil amendments as a result of their ability to supply nutrients and N₂O emissions that did not exceed that of the conventional urea fertilizer.     

Nitrous oxide production at different soil moisture contents in an arable soil in China

Abstract

Laboratory incubations were conducted to investigate nitrous oxide (N₂O) production from a subtropical arable soil (Typic Plinthodults) incubated at different soil moisture contents (SMC) and with different nitrogen sources using a 10% (v/v) acetylene (C₂H₂) inhibitory technique at 25°C. The production of N₂O and CO₂ was monitored during the incubations and changes in the contents of KCl-extractable NO^? ₃-N and NH⁺ ₄-N were determined. The production of N₂O increased slightly with an increase in SMC from 40% water-holding capacity (WHC) to 70% WHC, but increased dramatically at 100% WHC. After incubation the NO^? ₃-N content increased even at a SMC of 100% WHC. At a SMC of 100% WHC, the addition of NH⁺ ₄-N promoted the production of N₂O and CO₂, whereas the addition of NO^? ₃-N decreased N₂O production. Compared with the incubation without C₂H₂, the presence of C₂H₂ increased NH⁺ ₄-N content, but decreased NO^? ₃-N content, and there was no significant difference in N₂O production. These results indicate that heterotrophic nitrification contributes to N₂O production in the soil.     

Denitrification potentials: Measurement of seasonal variation using a short-term anaerobic incubation technique

A short-term anaerobic incubation technique using the C₂H₂ inhibition of N₂O-reductase for comparing denitrification potentials of soils is described. Twenty grams of soil with added NO^?1₃ are incubated in the presence of He and 0.1 atm C₂H₂ at 25°C and 0 soil matric potential for 8 h. N₂O evolution is linear within 60 to 120 min. The denitrification potential of soils stored at 4°C decreased markedly over 21 days of storage in accordance with changes in the available C. Denitrification under an anaerobic atmosphere was observed at 4 C. Denitrification potentials were independent of NO^?3₃ concentrations above 25 μg NO^?₃-N g^?1 soil. Biphasic linear rates of N₂O evolution were observed in one soil. Incubation of this soil with chloramphenicol suggested the first linear phase is attributable to the in situ enzyme activity at the time of sampling. The second linear phase is indicative of the dentrification potential and is attributed to the full induction of denitrifying enzymes. The denitrification potential of a soil was maintained at or close to the maximum for 8 months of the year. During midsummer months the denitrification potential decreased markedly and the soil demonstrated a biphasic rate of denitrification suggesting an in situ denitrification activity less than the maximum potential. Results indicate that the maximum denitrification potential of this soil may often be limited not by NO^?₃ but by available C.     

Production and consumption of N2O during denitrification in subtropical soils of China

Purpose

Nitrous oxide (N₂O) production and reduction rates are dependent on the interactions with each other and it is therefore important to evaluate them within the context of simultaneously operating N₂O emission and reduction. The objective of this study was to quantify the simultaneously occurring N₂O emission and reduction across a range of subtropical soils in China, to gain a mechanistic understanding of potential N₂O dynamics under the denitrification condition and their important drivers, and to evaluate the potential role of the subtropical soils as either sources or sinks of N₂O through denitrification.

Materials and methods

Soils (45, from a range of different land uses and soil parent materials) were collected from the subtropical region of Jiangxi Province, China, and tested for their potential capacity for N₂O emission and N₂O reduction to N₂ during denitrification. N₂O emission and reduction were determined in a closed system under N₂ headspace after the soils were treated with 200?mg?kg^?1 NO ₃ ^? -N and incubation at 30?°C for 28?days. The soil physical and chemical properties, the temporal variations in headspace N₂O concentration, and NO ₃ ^? -N and NH ₄ ⁺ -N concentrations in the soil slurry were measured.

Results and discussion

Variations in N₂O concentration (N) over incubation time (t) were consistent with an equation in which average R ²?=?0.84?±?0.11 (p?<?0.05): $ N = A \times \left( {1 - \exp \left( { - {k_1} \times t} \right)} \right) - B \times \exp \left( {{k_2} \times t} \right) $ , where A is the total N₂O emission during the incubation, B is a constant, and k ₁ and k ₂ are the N₂O emission constant and reduction constants, respectively. The results of the simulation showed that k ₁ was greater than k ₂. The reduced amount of NO ₃ ^? -N in the first 7?days of incubation and the N₂O emission rate (the percentage of A value relative to the amount of NO ₃ ^? -N reduced during the 28-day incubation, R _n) were able to explain 82.9?% (p?<?0.01) of the variation in total N₂O emission (A) during the incubation for the soil samples studied, indicating that the total amount of N₂O emitted was determined predominately by denitrification capacity. Soil organic carbon content and soil nitrogen mineralization are the key factors that determine differences in the amounts of reduced NO ₃ ^? -N among the soil samples. The R _n value decreased with increasing k ₂ (p?<?0.01), indicating that soils with higher N₂O reduction capacity under these incubation conditions would emit less N₂O per unit of denitrified NO ₃ ^? -N than the other soils. Results are valuable in the evaluation of net N₂O emissions in the subtropical soils and the global N budget.

Conclusions

In a closed, anaerobic system, variations in N₂O concentration in the headspace over the incubation time were found to be compatible with a nonlinear equation. Soil organic carbon and the amount of NH ₄ ⁺ -N mineralized from the organic N during the first 7?days of incubation are the key factors that determine differences in the N₂O emission constant (k ₁), the N₂O reduction constant (k ₂), the total N₂O emission during the incubation (A) and the N₂O emission rate (R _n).     

Wheat straw and its biochar had contrasting effects on soil C and N cycling two growing seasons after addition to a Black Chernozemic soil planted to barley

Application of crop residues and its biochar produced through slow pyrolysis can potentially increase carbon (C) sequestration in agricultural production systems. The impact of crop residue and its biochar addition on greenhouse gas emission rates and the associated changes of soil gross N transformation rates in agricultural soils are poorly understood. We evaluated the effect of wheat straw and its biochar applied to a Black Chernozemic soil planted to barley, two growing seasons or 15 months (at the full-bloom stage of barley in the second growing season) after their field application, on CO₂ and N₂O emission rates, soil inorganic N and soil gross N transformation rates in a laboratory incubation experiment. Gross N transformation rates were studied using the ¹⁵N isotope pool dilution method. The field experiment included four treatments: control, addition of wheat straw (30 t ha^?1), addition of biochar pyrolyzed from wheat straw (20 t ha^?1), and addition of wheat straw plus its biochar (30 t ha^?1 wheat straw + 20 t ha^?1 biochar). Fifteen months after their application, wheat straw and its biochar addition increased soil total organic C concentrations (p?=?0.039 and <0.001, respectively) but did not affect soil dissolved organic C, total N and NH₄ ⁺-N concentrations, and soil pH. Biochar addition increased soil NO₃ ^?-N concentrations (p?=?0.004). Soil CO₂ and N₂O emission rates were increased by 40 (p?p?=?0.03), respectively, after wheat straw addition, but were not affected by biochar application. Straw and its biochar addition did not affect gross and net N mineralization rates or net nitrification rates. However, biochar addition doubled gross nitrification rates relative to the control (p?2 and N₂O emissions and enhance soil C sequestration. However, the implications of the increased soil gross nitrification rate and NO₃ ^?-N in the biochar addition treatment for long-term NO₃ ^?-N dynamics and N₂O emissions need to be further studied.     

Temporal in situ dynamics of N<Subscript>2</Subscript>O reductase activity as affected by nitrogen fertilization and implications for the N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O + N<Subscript>2</Subscript>) product ratio and N<Subscript>2</Subscript>O mitigation

In vitro, high nitrate (NO₃ ^?) concentrations significantly inhibit N₂O reductase activity. However, little information is available on the in situ temporal effects of excessive N fertilization on soil N₂O reductase activity and the regulation of the N₂O/(N₂ + N₂O) product ratio in agricultural soil. This study examined the monthly in situ dynamics of NO₃ ^? concentration, N₂O reductase activity, and N₂O/(N₂ + N₂O) product ratio for 2 years in loamy soil that had received either continuous N fertilizer at 400 kg N ha^?1 year^?1 for 15 years (N400) or no N fertilizers (CK). N₂O reductase activity was significantly lower under the N400 treatment than under the CK and correlated negatively with soil NO₃ ^? concentration. The decrease in N₂O reductase activity resulted in the N₂O/(N₂ + N₂O) product ratio increasing. These results demonstrate that excessive N fertilization has the potential to increase N₂O emissions by reducing N₂O reductase activity in soils. These results highlight the need for N₂O mitigation options to embrace the reduction of soil NO₃ ^? concentrations.     

Short-term effects of ammonium nitrogen in upland pasture soil affected or not affected by cattle

The short-term effects of excessive NH₄⁺-N on selected characteristics of soil unaffected (low annual N inputs) and affected (high annual N inputs) by cattle were investigated under laboratory conditions. The major hypothesis tested was that above a theoretical upper limit of NH₄⁺ concentration, an excess of NH₄⁺-N does not further increase NO₃⁻ formation rate in the soil, but only supports accumulation of NO₂⁻-N and gaseous losses of N as N₂O. Soils were amended with 10 to 500 μg NH₄⁺-N g⁻¹ soil. In both soils, addition of NH₄⁺-N increased production of NO₃⁻-N until some limit. This limit was higher in cattle-affected soil than in unaffected soil. Production of N₂O increased in the whole range of amendments in both soils. At the highest level of NH₄⁺-N addition, NO₂⁻-N accumulated in cattle-affected soil while NO₃⁻-N production decreased in cattle-unaffected soil. Despite being statistically significant, observed effects of high NH₄⁺-N addition were relatively weak. Uptake of mineral N, stimulated by glucose amendment, decreased the mineral N content in both soils, but it also greatly increased production of N₂O.     

Nitrous oxide emission from wetland rice soil as affected by the application of controlled-availability fertilizers and mid-season aeration

 N₂O emission from a wetland rice soil as affected by the application of three controlled-availability fertilizers (CAFs) and urea was investigated through a pot experiment. N₂O fluxes from the N fertilized paddy soil averaged 44.8–69.3 μg N m^–2 h^–1 during the rice growing season, accounting for 0.28–0.51% of the applied N. The emission primarily occurred during the mid-season aeration (MSA) and the subsequent re-flooding period. Fluxes were highly correlated with the NO₃ ^– and N₂O concentrations in the soil water. As there were relatively large amounts of NH₄ ⁺-N present in the soil of the CAF treatments at the beginning of MSA, leading to large amounts of NO₃ ^–-N during the MSA and the subsequent re-flooding period, the tested CAFs were not effective in reducing N₂O emission from this paddy soil. The potential of applied CAFs to reduce N₂O emissions from paddy soil is discussed. Received: 25 May 1999     

Biodegradation of an oily waste as influenced by nitrogen forms and sources

Biodegradation rates of oily waste in soil can be limited by mineral nutrients, particularly N and P. A laboratory incubation experiment was carried out to investigate the influence of N forms, nitrate (NO^? ₃-N) vs ammonium nitrogen (NH⁺ ₄-N), and sources, i.e., the conjugate cations/anions, on C mineralization rate (CMR) was determined daily by measuring the CO₂ evolved using gas chromatography. The CMR and the cumulative C mineralized (CCM) varied with the form and/or the source of N applied. The greatest enhancement in CMR occurred in the NO^? ₃-treatments in which the source conjugate cation was Ca⁺². The addition of P fertilizer further enhanced C mineralization rates irrespective of the form and/or the source of N added. The results show that up to 45% of the added oily waste mineralized as CO₂-C in 28 d. The residual P and N (NO^? ₃-N plus NH⁺ ₄-N) data showed that approximately 90% of the added P and N were utilized for oil decomposition. The amount of residual NO^? ₃-N appeared to have an inverse relationship with CCM. The NO^? ₃-N utilization occurred at the expense of NH⁺ ₄-N and this was particularly high in the treatments which received P.     

Determination of kC and kNin situ for calibration of the chloroform fumigation-incubation method

¹⁴C-labelled glucose and ¹⁵N-labelled KNO₃ were added to soil and the microbial biomass during 42 days' incubation was estimated using the chloroform fumigation-incubation method (CFIM). By day 1, most of the glucose (1577 μgCg^?1 soil) was metabolized and 110 μg NO^?₃-Ng^?1 soil were immobilized. In situ values for the proportions of biomass C (k_C) and biomass N (k_N) mineralized during the 10 days after CHCl₃ fumigation were determined on the basis that the immobilized labelled C and N remaining in the soil at this time were present as living microbial cells and their associated metabolites. The tracer data indicated that biomass C could be calculated by applying a k_c value of 0.41 to the CO₂-C evolved from the fumigated sample without subtraction of an unfumigated “control”. Biomass N was estimated from the net NH₄^?-N accumulation during the fumigation-incubation. The problem of reimmobilization of NH⁺₄-N where organisms of wide C:N ratio occur was overcome by adjusting the value of k_N according to the ratio of CO₂-C evolved: net NH₄⁺-N accumulated during the fumigation-incubation (C_F:N_F).A C_F:N_F ratio of 6:1 resulted in a k_N of 0.30 whereas a ratio of 13:1 indicated a k_N of 0.20.     

Effects of organic material amendment and water content on NO, N2O, and N2 emissions in a nitrate-rich vegetable soil

Amending vegetable soils with organic materials is increasingly recommended as an agroecosystems management option to improve soil quality. However, the amounts of NO, N₂O, and N₂ emissions from vegetable soils treated with organic materials and frequent irrigation are not known. In laboratory-based experiments, soil from a NO ₃ ^? -rich (340 mg N?kg^?1) vegetable field was incubated at 30°C for 30 days, with and without 10 % C₂H₂, at 50, 70, or 90 % water-holding capacity (WHC) and was amended at 1.19 g?C kg^?1 (equivalent to 2.5 t?C ha^?1) as Chinese milk vetch (CMV), ryegrass (RG), or wheat straw (WS); a soil not amended with organic material was used as a control (CK). At 50 % WHC, cumulative N₂ production (398–524 μg N?kg^?1) was significantly higher than N₂O (84.6–190 μg N?kg^?1) and NO (196–224 μg N?kg^?1) production, suggesting the occurrence of denitrification under unsaturated conditions. Organic materials and soil water content significantly influenced NO emissions, but the effect was relatively weak since the cumulative NO production ranged from 124 to 261 μg N?kg^?1. At 50–90 % WHC, the added organic materials did not affect the accumulated NO ₃ ^? in vegetable soil but enhanced N₂O emissions, and the effect was greater by increasing soil water content. At 90 % WHC, N₂O production reached 13,645–45,224 μg N?kg^?1 from soil and could be ranked as RG?>?CMV?>?WS?>?CK. These results suggest the importance of preventing excess water in soil while simultaneously taking into account the quality of organic materials applied to vegetable soils.     

Nitrous oxide production in aerobic soils under varying pH,temperature and water content

Laboratory studies were conducted to evaluate the effect of soil pH, temperature and water content on the rate of nitrification and on the amount of N₂O evolved from samples of Plano silt loam soil. The rate of nitrification of added NH₄⁺-N increased with increasing soil pH (4.7, 5.1 and 6.7), temperature (10, 20 and 30°C) and water content (0.1, 0.2 and 0.3 m³ m^?3). At soil water contents of 0.1 and 0.2 m³ m^?3, corresponding to 18 and 36% water-filled pore space, respectively, N₂O evolution was proportional to NO₃^? production. Approximately 0.1–0.2% of the nitrified N was evolved as N₂O-N. At 0.3 m³ m^?3 water content (54% water-filled pore space) and 20 and 30°C, the ratio of N₂O-N evolved to N nitrified was significantly higher (range of 0.3–1.1%).An additional experiment was conducted using diurnally fluctuating temperatures (10–30°C). The pattern of N₂O evolution was markedly different when the system was sampled at 10 and 30°C than at 20°C. The apparent N₂O emission rates were approximately equal for 12-h periods during which the temperature increased from 10 to 30°C or decreased from 30 to 10°C. In contrast, the apparent N₂O emission rates were significantly lower for the 12-h period when the incubation flasks were sampled at 20°C following the daily minimum temperature compared to the 12-h period when the samplings were at 20°C following the daily maximum temperature. This provides additional evidence that temperature fluctuation in the surface soil is a factor in-observed diurnal variations in N₂O emissions under field conditions.Our findings indicate that an interaction of three factors (soil pH, temperature and water content) affects the amount of N₂O evolved during nitrification in soils. In relatively dry soils, estimated N₂O production of ca. 0.1–0.3% of the N nitrified may be sufficiently accurate. Much higher N₂O output can be expected following rainfall or irrigation. Diurnal variability in N₂O fluxes from soils due to fluctuating temperature is an additional uncertainty in quantifying N₂O production in field soils.