Mineralization Of Organic Nitrogen Research Articles

A ferrous oxalate mediated photo-Fenton system: Toward an increased biodegradability of indigo dyed wastewaters

This study assessed the applicability of a ferrous oxalate mediated photo-Fenton pretreatment for indigo-dyed wastewaters as to produce a biodegradable enough effluent, likely of being derived to conventional biological processes. The photochemical treatment was performed with ferrous oxalate and hydrogen peroxide in a Compound Parabolic Concentrator (CPC) under batch operation conditions. The reaction was studied at natural pH conditions (5–6) with indigo concentrations in the range of 6.67–33.33mgL−1, using a fixed oxalate-to-iron mass ratio (C2O42−/Fe2+=35) and assessing the system's biodegradability at low (257mgL−1) and high (1280mgL−1) H2O2 concentrations. In order to seek the optimal conditions for the treatment of indigo dyed wastewaters, an experimental design consisting in a statistical surface response approach was carried out. This analysis revealed that the best removal efficiencies for Total Organic Carbon (TOC) were obtained for low peroxide doses. In general it was observed that after 20kJL−1, almost every treated effluent increased its biodegradability from a BOD5/COD value of 0.4. This increase in the biodegradability was confirmed by the presence of short chain carboxylic acids as intermediate products and by the mineralization of organic nitrogen into nitrate. Finally, an overall decrease in the LC50 for Artemia salina indicated a successful detoxification of the effluent.

TiO2-photocatalyzed transformation of the recalcitrant X-ray contrast agent diatrizoate

Iodinated X-ray contrast media (ICM) are biologically recalcitrant chemicals that are often detected in wastewater-impacted environments at higher concentrations than other pharmaceutical micropollutants of concern. Diatrizoate is an anionic ICM that is especially resistant to conventional wastewater and drinking water treatment processes. This study examined the aqueous photocatalytic treatment of diatrizoate using nanophase titanium dioxide (TiO2). Experiments demonstrated that diatrizoate can be degraded in aqueous TiO2 suspensions illuminated with ultraviolet-A (UVA) light. In oxic solutions, diatrizoate degraded principally via oxidation by adsorbed hydroxyl radicals (OH), releasing iodine substituents stoichiometrically, but causing little mineralization of organic carbon and nitrogen. Introduction of OH scavengers significantly slowed the rate of photocatalytic degradation. At circumneutral pH, diatrizoate was oxidized much more slowly than iopromide, a nonionic ICM, in part because of unfavorable electrostatic interactions with the negatively charged TiO2 surface; increased rates of oxidation observed at lower pH conditions can be attributed to more favorable diatrizoate-TiO2 sorptive interactions. Experiments also demonstrated that diatrizoate was degraded at appreciable rates in anoxic solutions, and reductive dehalogenation products are identified by liquid chromatography–mass spectrometry. The higher selectivity of reductive processes suggests a promising strategy for targeted treatment of recalcitrant ICM in organic-rich matrices like wastewater effluent.

The Brighton treatment wetlands

The Town of Brighton, Ontario implemented a 6.2ha marsh in 2000, for the purpose of improving water quality before discharge to receiving waters. The wetlands have successfully operated in this moderately cold climate for over ten years. Phosphorus removal of 2.3gP/(m2yr) was achieved, with an annual areal rate coefficient of 9.2m/yr. The removal is strongly seasonal, with the greatest reductions occurring in spring. The total nitrogen loading was dominated by ammonia (208gN/(m2yr)), with smaller amounts of organic and oxidized nitrogen. Ammonia was reduced to 173gN/(m2yr). Implied areal rate constants were high for mineralization of organic nitrogen (29m/yr) and denitrification (101m/yr), but low for nitrification (4m/yr). CBOD5 was reduced from 5.4 to 3.2mg/L, and TSS was reduced from 13.2 to 7.2mg/L, both with slightly higher values during late winter. The wetland was not effective in reducing pathogens, with Escherichia coli at 167cfu/100ml entering, and 132cfu/100ml leaving. Vegetation was sparse, likely due to muskrats and deep water. Macro-invertebrate diversity was lower than for regional wetlands. Bird use was very high, and birding was a popular human activity. The wetland has been designated as provincially significant.

Adsorption and photocatalytic degradation of cysteine in presence of TiO2

Abstract Amino-acids are elemental constituents of microorganisms, e.g. bacteria, fungi, virus, mold, among others and are at the origin of the formation of odorous compounds after chlorination treatment due to the filtration of these microorganisms. Our study aims at studying the photocatalytic degradation of cysteine chosen as model of amino acid for understanding better the photocatalytic chemical pathway of microorganisms. The kinetics of adsorption in the dark and under UV light, the kinetics of photocatalytic oxidation, the effect of pH and the main initial pathways of cysteine degradation have been investigated in aerated TiO 2 Degussa P-25 aqueous suspensions illuminated at λ > 340 nm. Langmuir and Langmuir–Hinshelwood kinetics were observed respectively in the dark and under UV light. The coverage of TiO 2 surface under UV revealed a coverage of TiO 2 equivalent to that in the dark, indicating no modification of adsorption sites under irradiation. This behaviour is in agreement with a geometrical adsorption of cysteine as proved by using the molecular surface of cysteine and by taking into account the accessibility of water molecules. The effect of pH on adsorption and photocatalytic degradation showed a good correlation between dark adsorption and photocatalytic degradation. The mineralisation of organic carbon and nitrogen shows the presence of traces of organics hardly mineralisable but also the formation of similar amount of NH 4 + and NO 3 − ions from the beginning of the reaction contrarily to what was observed for other amino-acids. This behaviour is explained by the different ionisation states of cysteine. Taking into account the evolution of Total Organic Carbon, sulphate, nitrate and ammonium, an initial reaction pathway has been proposed.

Effects of Inoculating Thermophiles and Rhizopus on Composting Process of Vinegar Residue and their Nutrients Status

In order to increase the efficiency of composting vinegar residue, the effect of different strain combination,a thermophiles(OP-2) and two rhizopus(FM1,SL10) combined,on the composting pocess and effect was studied. The results showed: Inoculating thermophilic bacteria OP-2 can increase the speed of composting vinegar residue, which can increase the heap temperature to 70°C in 7days ahead. Also inoculating inocula accelerated the mineralization of organic nitrogen. In the end of composting, the contents of total nitrogen、total phosphorus and total potassium, as well as GI were higher than the control treatment, which showed that inoculating inocula can accelerate the maturity process of composting vinegar residue and increase the composting quality.

Use of crop residues with alkaline slag to ameliorate soil acidity in an Ultisol

AbstractInformation regarding the interaction between liming agents and crop residues on soil acidity amelioration is limited. A laboratory incubation study was undertaken to investigate the combined application of alkaline slag (AS, the major component is CaO) and crop residues with different C/N ratios and ash alkalinity content. Incorporation of amendments was effective in reducing soil exchangeable acidity and Al saturation and increasing exchangeable base cations (P < 0.05), but the effect of AS on soil pH adjustment was reduced when added with a high amount of residue with a low C/N ratio. Initial increases in soil pH were attributed to the release of alkalinity from the combined amendments and the mineralization of organic nitrogen (N). During subsequent incubation, the soil pH decreased because of nitrification. Crop residues with a high C/N ratio increased N immobilization and reduced net nitrification, resulting in a slight pH decrease. Crop residues with a low C/N ratio resulted in a sharp decrease in soil pH when applied with low levels of AS because of stimulated soil nitrification, whereas high AS had no consistent effect on net nitrification. Hence, compared to the control (pH = 4.21), a large increase in soil pH occurred, especially when peanut straw was applied at 10 g/kg (pH = 5.16). It is suggested that crop residues with high C/N ratio and also combined with a liming agent such as AS are preferred to ameliorate soil acidity. The liming effect of AS is likely to be negated if added in combination with residues with high N contents.

Legacies of plant litter on carbon and nitrogen dynamics and the role of the soil community

Abstract There is increasing awareness of the importance of ecological legacies in contemporary ecosystem processes. Decomposition is regulated by a set of interacting hierarchically organized factors. As spatial and temporal scales decrease, decomposition is largely dependent on the quality of resources and the decomposer community, but whether and how these factors manifest via historical legacy effects is not well understood. We tested whether the history of plant litter inputs had short-term legacy effects on contemporary litter and soil organic matter carbon (C) and nitrogen (N) mineralization. Using a field/laboratory microcosm approach, we exposed soils to two litters of contrasting chemistry and, after adding fresh substrates, we monitored C and N dynamics. In a parallel experiment, we manipulated the soil community to reduce litter-history impacts on its composition and size to investigate whether the soil community could be an important contributor to legacy effects We found strong short-term litter legacy effects on contemporary litter and soil N mineralization, the duration of which was dependent on the contemporary substrate for decomposition. These strong effects were not consistent with the home field advantage phenomenon, as exposure to a specific litter did not favor the decomposition of the same litter when it was applied as a contemporary substrate. Reduction of the litter-history effects on soil biota decreased the impact of litter history on N immobilization, suggesting that plant litter impacts on the soil community may be an important component of plant litter legacies on N decomposition. In contrast to N, litter legacies appeared to be much less important for C decomposition, suggesting that legacy effects might uncouple contemporary C and N dynamics.

Organic nitrogen mineralisation in two contrasting agro-ecosystems is unchanged by biochar addition

Biochar additions to soil have been reported to enhance soil fertility whilst simultaneously storing carbon (C). We tested whether either fresh or field-conditioned (aged) biochar amendment to two contrasting agricultural soils would alter the mineralisation of organic N compounds. The mineralisation of 14C-labelled amino acids and peptides were determined over 20 days within each soil. An exponential kinetic decay model was subsequently fitted to the mineralisation data. Overall, statistical analysis revealed significant but small differences between the two biochar treatments and the unamended control treatment. We conclude that biochar has very limited impact on the mineralisation rate of low molecular weight dissolved organic N compounds in these agro-ecosystems.

Nitrification and microbiological evolution during aerobic treatment of municipal solid wastes

Nitrification is a key step in the nitrogen cycle in various ecosystems. In this study, the nitrogen dynamic and the evolution of groups of microorganisms were studied during aerobic treatment of fine organic fraction of municipal solid wastes. Mineralization of organic nitrogen exhibited two phases and resulted in two ammonia emissions peaks. The nitrogen balance indicated the onset of nitrification only during the maturation stage, which was confirmed by the accumulations of both nitrite and nitrate and the nitrous oxide emissions in this period. A significant development of ammonia-oxidizing bacteria correlated to the onset of nitrification. On the contrary, ammonia-oxidizing archaea were less abundant and declined through treatment. Identification of these ammonia oxidizers indicates that the Nitrosomonas europaea/eutropha-like ammonia oxidizing bacteria were responsible for ammonia oxidation instead of other groups of ammonia oxidizers during aerobic treatment of fine organic fraction of municipal solid wastes.

Ammonium release from a blanket peatland into headwater stream systems

Hydrochemical sampling of South Pennine (UK) headwater streams draining eroded upland peatlands demonstrates these systems are nitrogen saturated, with significant leaching of dissolved inorganic nitrogen (DIN), particularly ammonium, during both stormflow and baseflow conditions. DIN leaching at sub-catchment scale is controlled by geomorphological context; in catchments with low gully densities ammonium leaching dominates whereas highly gullied catchments leach ammonium and nitrate since lower water tables and increased aeration encourages nitrification. Stormflow flux calculations indicate that: approximately equivalent amounts of nitrate are deposited and exported; ammonium export significantly exceeds atmospheric inputs. This suggests two ammonium sources: high atmospheric loadings; and mineralisation of organic nitrogen stored in peat. Downstream trends indicate rapid transformation of leached ammonium into nitrate. It is important that low-order headwater streams are adequately considered when assessing impacts of atmospheric loads on the hydrochemistry of stream networks, especially with respect to erosion, climate change and reduced precipitation.

Estimating mineralisation of organic nitrogen from biosolids and other organic wastes applied to soils in subtropical Australia

One major benefit of land application of biosolids is to supply nitrogen (N) for agricultural crops, and understanding mineralisation processes is the key for better N-management strategies. Field studies were conducted to investigate the process of mineralisation of three biosolids products (aerobic, anaerobic, and thermally dried biosolids) incorporated into four different soils at rates of 7–90 wet t/ha in subtropical Queensland. Two of these studies also examined mineralisation rates of commonly used organic amendments (composts, manures, and sugarcane mill muds). Organic N in all biosolids products mineralised very rapidly under ambient conditions in subtropical Queensland, with rates much faster than from other common amendments. Biosolids mineralisation rates ranged from 30 to 80% of applied N during periods ranging from 3.5 to 18 months after biosolids application; these rates were much higher than those suggested in the biosolids land application guidelines established by the NSW EPA (15% for anaerobic and 25% for aerobic biosolids). There was no consistently significant difference in mineralisation rate between aerobic and anaerobic biosolids in our studies. When applied at similar rates of N addition, other organic amendments supplied much less N to the soil mineral N and plant N pools during the crop season. A significant proportion of the applied biosolids total N (up to 60%) was unaccounted for at the end of the observation period. High rates of N addition in calculated Nitrogen Limited Biosolids Application Rates (850–1250 kg N/ha) resulted in excessive accumulation of mineral N in the soil profile, which increases the environmental risks due to leaching, runoff, or gaseous N losses. Moreover, the rapid mineralisation of the biosolids organic N in these subtropical environments suggests that biosolids should be applied at lower rates than in temperate areas, and that care must be taken with the timing to maximise plant uptake and minimise possible leaching, runoff, or denitrification losses of mineralised N.

Erratum to: Estimating mineralisation of organic nitrogen from biosolids and other organic wastes applied to soils in subtropical Australia

One major benefit of land application of biosolids is to supply nitrogen (N) for agricultural crops, and understanding mineralisation processes is the key for better N-management strategies. Field studies were conducted to investigate the process of mineralisation of three biosolids products (aerobic, anaerobic, and thermally dried biosolids) incorporated into four different soils at rates of 7?90 wet t/ha in subtropical Queensland. Two of these studies also examined mineralisation rates of commonly used organic amendments (composts, manures, and sugarcane mill muds). Organic N in all biosolids products mineralised very rapidly under ambient conditions in subtropical Queensland, with rates much faster than from other common amendments. Biosolids mineralisation rates ranged from 30 to 80% of applied N during periods ranging from 3.5 to 18 months after biosolids application; these rates were much higher than those suggested in the biosolids land application guidelines established by the NSW EPA (15% for anaerobic and 25% for aerobic biosolids). There was no consistently significant difference in mineralisation rate between aerobic and anaerobic biosolids in our studies. When applied at similar rates of N addition, other organic amendments supplied much less N to the soil mineral N and plant N pools during the crop season. A significant proportion of the applied biosolids total N (up to 60%) was unaccounted for at the end of the observation period. High rates of N addition in calculated Nitrogen Limited Biosolids Application Rates (850?1250 kg N/ha) resulted in excessive accumulation of mineral N in the soil profile, which increases the environmental risks due to leaching, runoff, or gaseous N losses. Moreover, the rapid mineralisation of the biosolids organic N in these subtropical environments suggests that biosolids should be applied at lower rates than in temperate areas, and that care must be taken with the timing to maximise plant uptake and minimise possible leaching, runoff, or denitrification losses of mineralised N.

Vertical distribution of soluble organic nitrogen, nitrogen mineralization, nitrification, and amidohydrolase activities in a manure‐treated soil

AbstractRecent studies indicate that soil soluble organic nitrogen (SON) plays an important regulatory role in the soil–plant N cycle. The aims of this study were to identify the vertical distribution of SON and its correlation with N mineralization, nitrification, and amidohydrolase activities, in a soil repeatedly amended with cow manure or chemical fertilizer. For this purpose, soil samples were collected from 0–20, 20–40, 40–60, 60–80, and 80–100 cm depths of a calcareous soil, which has been annually amended for 5 y with cow manure (CM) at two rates of 50 (CM50) and 100 (CM100) Mg CM ha–1 y–1. Treatments with chemical fertilizer (CF) and a control (CT) were also included. Soluble organic N, N mineralization, nitrification rates, as well as L‐glutaminase and L‐asparaginase activities were determined. Both CM50 and CM100 enhanced SON content throughout the soil profile. Nitrogen‐mineralization rate (Nm) was increased at the 0–20 cm depth of the CM100 treatment and remained unaffected at the deeper depths. Nitrification rate (Nn) was significantly higher at the 0–60 cm depth of CM100 compared to CF and CT. L‐glutaminase and L‐asparaginase activities were significantly increased at the 0–40 cm depth in both CM50 and CM100 compared to CF and CT. The amidohydrolase activities could not be detected below 40 cm, regardless of the fertilizer treatments. Our results suggest that SON makes a minor contribution to N mineralization in deep soil layers. It was also concluded that changes in the SON throughout the soil profile were not associated with changes in the N‐transformation rates (Nm and Nn) and amidohydrolase activities. While we conclude that SON is a major N pool in the whole profile of the manure applied soil further investigation is required to characterize SON and to investigate the bioavailability of SON for microbial activity in different soil depths.

Introducing Acacia mangium trees in Eucalyptus grandis plantations: consequences for soil organic matter stocks and nitrogen mineralization

Background and aims Eucalyptus plantations cover 20 million hectares on highly weathered soils. Large amounts of nitrogen (N) exported during harvesting lead to concerns about their sustainability. Our goal was to assess the potential of introducing A. mangium trees in highly productive Eucalyptus plantations to enhance soil organic matter stocks and N availability.

Incorporation of Municipal Biosolids Affects Organic Nitrogen Mineralization and Elephantgrass Biomass Production

Municipal biosolids (MBS) represents an alternative source of nutrients for the production of bioenergy crops like elephantgrass (Pennisetum purpureum Schum.). Two experiments were conducted during 2 yr in Florida to evaluate the effect of soil incorporation vs. surface application of MBS on: (i) elephantgrass dry matter (DM) yield, tissue N and P concentration and removal, and soil C and P (Exp. 1); and (ii) organic N mineralization and DM decomposition rates of MBS measured in the field using a litter bag incubation technique (Exp. 2). In Exp. 1, three treatments supplied 350 kg total N ha−1 yr−1 from surface‐applied municipal biosolids (MBS‐SA), soil‐incorporated municipal biosolids (MBS‐INC), and surface‐applied ammonium nitrate (NH4NO3). A fourth treatment provided 700 kg total N ha−1 yr−1 from MBS‐SA (double rate of municipal biosolids, 2x‐MBS). In Exp. 2, MBS was field incubated in litter bags placed on the soil surface or at a 5‐cm soil depth. Elephantgrass DM yield, and N and P removal were greater for MBS‐INC than MBS‐SA. Dry matter yield for MBS‐INC was not different than for NH4NO3 fertilizer (22.5 vs. 24.3 Mg ha−1). Removal of N and P increased 39 and 10 kg ha−1 yr−1, respectively, for MBS‐INC and MBS‐SA. Total organic N mineralized was greater for MBS‐INC (386 g kg−1) than MBS‐SA (308 g kg−1). Incorporation of MBS increases elephantgrass DM yield and nutrient removal compared to surface application and allows MBS to replace a greater proportion of inorganic N fertilizer.

Microbial mineralization of organic nitrogen into nitrate to allow the use of organic fertilizer in hydroponics

Hydroponics is an excellent technique for the cultivation of vegetable crops and other plants, but organic fertilizers cannot be used in conventional hydroponic systems, which generally use only inorganic fertilizers, because organic compounds in the hydroponic solutions generally have phytotoxic effects that lead to poor plant growth. Few microorganisms are present in hydroponic solutions to mineralize the organic compounds into inorganic nutrients. In this article a novel and practical hydroponic culture method that uses microorganisms to degrade organic fertilizer in the hydroponic solution has been developed. Soil microorganisms were cultured by regulating the amounts of organic fertilizer and inoculum, with moderate aeration. The microorganisms mineralized organic nitrogen via ammonification and nitrification into nitrate at an efficiency of 97.6%. The culture solution containing the microorganisms was usable as a hydroponic solution, and organic fertilizer could be directly added to it during vegetable cultivation. Vegetables grew well in the organic hydroponic system. Organic hydroponics based on this method is therefore a practical tool for the utilization of organic sources of fertilizer.

Surprisingly rapid nitrogen cycling in tropical forest plantations on volcanically derived soils

Secondary forests and young forest plantations frequently have high rates of tree growth and NPP – higher even than mature forests in similar situations. The nutrients required to sustain this rapid growth are derived from the soil and by external inputs such as rainfall or, in the case of nitrogen, by biological N fixation. In our study of the effects of tree species within replicated experimental plantations in a moist, lowland tropical environment in Costa Rica, high rates of biomass accumulation and productivity were coupled with high rates of N accumulation and cycling. We applied extensive sampling through time within a mass-balance approach to address the question “Where does all the nitrogen come from?”Rates of N uptake by the vegetation in these plantations were extraordinarily high, even by tropical forest standards, reaching 412 kg N ha^-1^ yr^-1^. Rapid decay coupled to tight nitrogen cycling may have provided large amounts of available N for plant uptake, but do not explain the large quantities of N that accrued in the vegetation, up to 1075 kg N/ha over 16 years. Surface soil organic matter stocks in the plantations increased by as much as 320 kgC/ha in surface soils, but soil nitrogen varied differently. Soil N stocks to 1 m depth were depleted by an average of 2119 kg/ha relative to the mature forest. Thus, mineralization of soil organic nitrogen could have supplied the N that accrued in biomass over the 16-yr period, but this apparently occurred without concomitant net loss of soil C. The C:N ratios of soil organic matter (SOM)in the plantations indicated either replacement of SOM with more C-rich detritus or selective removal of N from existing SOM. Regardless, high productivity in these plantations apparently was supported in part by mining of soil nitrogen. Species varied, however. Depletion of soil N stocks was only 219 kg/ha under Vochysia guatemalensis, in which 1075 kgN/ha had accrued. Asymbiotic N fixation is the next most plausible mechanism for supplying plant-available N, and may be enhanced in stands with high availability of recently produced photosynthates.

Surprisingly rapid nitrogen cycling in tropical forest plantations on volcanically derived soils

AbstractSecondary forests and young forest plantations frequently have high rates of tree growth and NPP – higher even than mature forests in similar situations. The nutrients required to sustain this rapid growth are derived from the soil and by external inputs such as rainfall or, in the case of nitrogen, by biological N fixation. In our study of the effects of tree species within replicated experimental plantations in a moist, lowland tropical environment in Costa Rica, high rates of biomass accumulation and productivity were coupled with high rates of N accumulation and cycling. We applied extensive sampling through time within a mass-balance approach to address the question “Where does all the nitrogen come from?”Rates of N uptake by the vegetation in these plantations were extraordinarily high, even by tropical forest standards, reaching 412 kg N ha^-1^ yr^-1^. Rapid decay coupled to tight nitrogen cycling may have provided large amounts of available N for plant uptake, but do not explain the large quantities of N that accrued in the vegetation, up to 1075 kg N/ha over 16 years. Surface soil organic matter stocks in the plantations increased by as much as 320 kgC/ha in surface soils, but soil nitrogen varied differently. Soil N stocks to 1 m depth were depleted by an average of 2119 kg/ha relative to the mature forest. Thus, mineralization of soil organic nitrogen could have supplied the N that accrued in biomass over the 16-yr period, but this apparently occurred without concomitant net loss of soil C. The C:N ratios of soil organic matter (SOM)in the plantations indicated either replacement of SOM with more C-rich detritus or selective removal of N from existing SOM. Regardless, high productivity in these plantations apparently was supported in part by mining of soil nitrogen. Species varied, however. Depletion of soil N stocks was only 219 kg/ha under Vochysia guatemalensis, in which 1075 kgN/ha had accrued. Asymbiotic N fixation is the next most plausible mechanism for supplying plant-available N, and may be enhanced in stands with high availability of recently produced photosynthates.

Quantifying Nitrogen Process Rates in a Constructed Wetland Using Natural Abundance Stable Isotope Signatures and Stable Isotope Amendment Experiments

This study describes the spatial variability in nitrogen (N) transformation within a constructed wetland (CW) treating domestic effluent. Nitrogen cycling within the CW was driven by settlement and mineralization of particulate organic nitrogen and uptake of NO3-. The concentration of NO3- was found to decrease, as the delta15N-NO3- signature increased, as water flowed through the CW, allowing denitrification rates to be estimated on the basis of the degree of fractionation of delta15N-NO3-. Estimates of denitrification hinged on the determination of a net isotope effect (eta), which was influenced byprocesses that enrich or deplete 15NO3- (e.g., nitrification), as well as the rate constants associated with the different processes involved in denitrification (i.e., diffusion and enzyme activity). The influence of nitrification on eta was quantified; however, it remained unclear how eta varied due to variability in denitrification rate constants. A series of stable isotope amendment experiments was used to further constrain the value of eta and calculate rates of denitrification, and nitrification, within the wetland. The maximum calculated rate of denitrification was 956 +/- 187 micromol N m(-2) h(-1), and the maximum rate of nitrification was 182 +/- 28.9 micromol N m(-2) h(-1). Uptake of NO3- was quantitatively more important than denitrification throughoutthe wetland. Rates of N cycling varied spatially within thewetland, with denitrification dominating in the downstream deoxygenated region of the wetland. Studies that use fractionation of N to derive rate estimates must exercise caution when interpreting the net isotope effect. We suggest a sampling procedure for future natural abundance studies that may help improve the accuracy of N cycling rate estimates.

Effect of Salt Stress on Decomposition of Organic Matter and Nitrogen Mineralization in Animal Manure Amended Soils

As it is believed that soil salinity can alter the organic matter turnover process, the present study discussed the influence of soil salinity on the decomposition of organic matter and nitrogen mineralization in animal manure amended soils. A factorial combination of two soil types (saline and non-saline soils) with three types of animal manure (i.e. poultry manure, goat manure and cow dung) was used to assess the C and N mineralization. The amount of CO2-C released from both soils was not significant (P ≤ 0.05) until day 2 of incubation. However, as incubation progressed, the amount of CO2-C released from manure amended soils was found to be significantly (P ≤ 0.05) higher than that of the control. However in the case of cow dung amended soils, release of CO2-C was not much influenced by the salinity stress. The NH4+ -N content of both soils was found to be reached to the peak at day 14, followed by gradual reductions in all treatments. However, saline soil showed significantly (P ≤ 0.05) low NH4+ -N content compared to the non-saline soil. Though, the nutritional composition of applied manures was different, no significant (P ≤ 0.05) differences were found among the treatments in terms of N mineralization. Furthermore, no distinct pattern of treatment behavior could be observed for NO2- -N contents also. However, the content of NO3- -N was found to be dominated in non-saline soil throughout the incubation. Results could be concluded that the response pattern of C and N mineralization to salinity stress depended on the type of animal manure incorporate to the soil and duration of incubation. Key words: salinity stress; animal manure; decomposition of organic matter; nitrogen mineralization DOI: 10.4038/jas.v5i1.2319 Journal of Agricultural Sciences Vol.5(1) 2010 pp.9-18