The ammonia removal ability of heterotrophic bacteria Alcaligenes faecalis strain No.4 isolated from sewage sludge was examined in a batch operation to mitigate ammonia from piggery wastewater, consequently preventing pollution by the inflow of wastewater from piggeries adjacent to rivers. If this process works functionally, it can be effective in controlling nitrous oxide (N2O) and nitrate (NO3−) emissions derived from animal agriculture, the heterotrophic nitrifying and the aerobic denitrifying effect of A. faecalis strain No.4 on high-strength ammonium (NH4+-N) were evaluated in wastewater collected from a piggery. The removal rate by A. faecalis strain No.4 on high-strength ammonium (NH4+-N) was 0.97 kg N/m3/day which was more than 100 fold greater than that achieved using conventional aerobic nitrification and anaerobic denitrification processes. An aerobic one-step denitrification system using A. faecalis strain No.4 can be proposed to remove ammonia and phytopathogens from piggery wastewater with high efficiency and prevent water pollution in adjacent rivers.

Urine is a critical nitrogen (N) input in temperate grazed grasslands and can drive substantial nitrous oxide (N2O) production in soils. However, it remains unclear how differences in the N input rate affect N2O fluxes and vary between different grassland soils. The effect of increasing urine N application on ammonium (NH4+), nitrite (NO2−) and nitrate (NO3−) concentrations and N2O production was tested in two grassland soils, a free-draining loam and an imperfectly drained sandy-loam. It was hypothesized that high-urine N application rates would lead to ammonia/ammonium (NH3/NH4+) accumulation influencing N transformation rates and N2O production which differ between grassland soils. Fresh cattle urine was applied at rates equivalent to 300 and 1000 kg N/ha in an aerobic incubation experiment. Soils were destructively sampled over 80 days to measure changes in inorganic-N and pH. The higher N addition rate was associated with elevated NH3 concentrations up to day 35 in soils, probably inhibiting NO2− to NO3− reduction. In contrast, there was no inhibition of nitrification in the 300 kg N/ha treatment. Cumulative N2O fluxes were greatest from the 300 kg N/ha treatment for the loam soil, but were greater for the sandy-loam under the 1000 kg N/ha treatment. The results also show that differences in soil properties, in particular carbon availability, can be important in regulating N transformation and N2O production. Collectively, these results demonstrate the proposed mechanism of nitrification inhibition at high-N input rates, driven by either high NH3/NH4 and/or increased levels of NH4HCO3 from urea hydrolysis.

Nitrification potential of a tropical vertisol saturated with water was estimated during sequential reduction of nitrate (NO3−), ferric iron (Fe3+), sulphate (SO42−) and carbon dioxide (CO2) in terminal electron-accepting processes (TEAPs). In general, the TEAPs enhanced potential nitrification rate (PNR) of the soil. Nitrification was highest at Fe3+ reduction followed by SO42− reduction, NO3− reduction and lowest in unreduced control soil. Predicted PNR correlated significantly with the observed PNR. Electron donor Fe2+ stimulated PNR, while S2− inhibited it significantly. Terminal-restriction fragment length polymorphism targeting the amoA gene of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) highlighted population dynamics during the sequential reduction of terminal electron acceptors. Only the relative abundance of AOA varied significantly during the course of soil reduction. Relative abundance of AOB correlated with NO3− and Fe2+. Linear regression models predicted PNR from the values of NO3−, Fe2+ and relative abundance of AOA. Principal component analysis of PNR during different reducing conditions explained 72.90% variance by PC1 and 19.52% variance by PC2. Results revealed that AOA might have a significant role in nitrification during reducing conditions in the tropical flooded ecosystem of a vertisol.

Medusahead is an invasive annual grass that, once established, severely affects range-land productivity and stability. Medusahead builds large seedbanks in the litter and on the soil surface. Effective weed control of medusahead involves either inhibiting germination from the seedbank, eliminating the seedbank, or enhancing germination so that plants are available for control. The purpose of this study was to determine the influence of nitrogen enrichment, immobilization, and nitrification inhibition treatments in the field on the size and germination status of medusahead seedbanks. The germination status of medusahead seeds in seedbanks was determined by periodically collecting field samples of surface soil and litter and bioassaying them in greenhouse emergence tests. Control seedbanks had increased seedling emergence with KNO3 or GA3 enrichment of the bioassay substrate. The combination of these two materials increased emergence. Nitrogen enrichment increased seedling establishment in the field. Carbon enrichment in the field decreased seedling establishment and increased medusahead seeds in seedbanks. Nitrapyrin treatment decreased medusahead in the field similar to carbon enrichment. In comparison to the control or other treatments, GA3 enrichment was not as effective in increasing emergence from nitrapyrin-treated bioassay samples. The combination of carbon and nitrapyrin treatments was very effective in eliminating medusahead emergence in the field, but in wetter years, it never completely eliminated medusahead seedling recruitment and subsequent reproduction. These treatments have promise for influencing succession in medusahead infestations if an adapted perennial species, capable of competing under low nitrogen levels, becomes available.

Ammonia (NH3) emissions from poultry farming operations have become a crucial concern due to their potential adverse effects on performance, birds and human health, and the environment. Due to genetic improvements, current commercial poultry require high quality balanced nutrition to maintain their rapid growth and production. Amino acids are components of protein nutrition that greatly influence the growth of the birds, and methionine is the first limiting essential amino acid in the high protein diets of poultry. However, excess or misuse of amino acid supplementation to poultry diets increases nitrogen (N) excretion and emissions to the environment. Currently, there are limited numbers of research publications regarding NH3 emissions from poultry manure, and few of them address manure enhancement by microbial nitrification. Therefore, the aim of this review is to evaluate the potential of soil nitrifying bacteria to reduce NH3 volatilisation and enhance N retention in poultry manure. This review presents the current status of knowledge regarding soil nitrifying bacteria, NH3 nitrification, and summarises the strategies to enhance microbial nitrification of poultry manure, and the environmental ramifications when using different techniques to control NH3 emissions. In spite of the fact that there are few research studies on reducing NH3 volatilisation through nitrification, it has been concluded that nitrification would be a sustainable method for mitigating N excretion and NH3 emission from poultry; however, further research is needed to identify the proper nitrifying bacteria to enhance microbial nitrification.

This study investigated the effects of mistletoe infection on N cycling in a semi–arid savanna, south-west Zimbabwe. We established five plots (10 × 10 m) which each included three large canopy-dominant Acacia karroo trees infected by one of three mistletoes (Erianthemum ngamicum, Plicosepalus kalachariensis and Viscum verrucosum) and non-infected A. karroo trees. In each plot, we measured litterfall, litter quality (N, phenolics, tannins and lignin), soil nutrient concentrations and N transformations beneath tree canopies. Soil N, P and Ca were greatest beneath trees infected by P. kalachariensis than beneath non-infected trees. Litterfall and litter N returns were 1.5, 2 and 1.4 times more beneath A. karroo trees infected by E. ngamicum, P. kalachariensis and V. verrucosum, respectively. Mineral N increased with mistletoe infection but did not exceed 20%. Soil N transformations were greater beneath trees infected by E. ngamicum (> 40%), and lower beneath trees infected by P. kalachariensis (<50%) and V. verrucosum (<48%) than beneath non-infected A. karroo trees. Soil N transformations were negatively correlated with condensed tannins, lignin and lignin : N. We conclude that the improved N concentration can increase resource heterogeneity, which may alter the ecosystem structure and functioning in the semi-arid savanna.

We have studied a number of related processes of the nitrogen cycle in a Brazilian floodplain lake to identify the major pools and pathways over a short time period. The study was centred on the littoral zone dominated by the floating plant Eichhornia azurea, which has a large epiphyte algal community of which heterocystous cyanobacteria were the major components. The water column was continuously undersaturated with oxygen although some elevated values (to 60% saturation) were recorded in the macrophyte beds in the afternoon. Marked diel temperature changes were documented. NH4-N dominated the dissolved N component in the water with maximal values (60 mg m−3) at lowest O2, concentrations early in the morning. Nitrogen fixation (acetylene reduction) of the epiphyte community showed marked diel changes with daily values of 5 mg N fixed m−2 day−1 (based on 3:1 C2H4:N2 ratio). Macrophyte NH4-N uptake rates (in situ incubations) were 93 mg N m−2 day−1. The activities of nitrifying bacteria could not be detected with the nitrapyrin block on dark CO2 fixation but denitrification (acetylene block technique) was recorded in the sediments when enhanced with NO-3. The major pathways of aquatic nitrogen involved macrophyte uptake and sediment release of NH4-N.

Soil mineralization and nitrification rates were measured in (1) undisturbed and felled gaps of varying size in terra firme forest, and (2) along a forest – savanna transect, on Ilha de Maracá in northern Brazil. Both rates were similar to those found in studies of other forests with a marked seasonal rainfall pattern. However, rates were much lower than those of tropical forests where there is little seasonality in rainfall. A major finding was that the highest rates were during the transition between dry and wet seasons, implying that wetting and drying may be an important initiator of soil nitrogen flux. Felling had little effect on either process up to a gap size of 2500 m2. In the forest-savanna study, nitrogen mineralization was lower in the savanna in all seasons, but in the wet season when the savanna soils were water-logged NH4+-N was immobilized. Experimental additions of nutrients identified two important results; first that added NH4+-N was quickly immobilized rather than nitrified – this may be an important nutrient conservation mechanism, and second that soil calcium appeared to be a limiting factor, either directly or through a pH effect.

Seasonally flooded forests represent a transition between terrestrial and aquatic ecosystems. The Mapire river, a tributary of the Orinoco river, floods its surrounding forests during the wet season (May–December). The soils are very acid and the total nitrogen concentration (0.1%) is only half that found in nearby soils flooded by Orinoco waters. Ammonium-nitrogen predominates in the soil during the flooded period while nitrate-nitrogen concentrations are higher in the dry period. Wide fluctuations in the inorganic nitrogen fractions did not considerably affect the annual course of soil nitrogen.

The predominance of mineralization versus nitrification (56 and 5 μg soil month−1 respectively) and possibly the synchronization of nitrogen availability with plant demand could be considered as nitrogen conserving mechanisms.

In synchrony with the hydrologic cycle, the seasonally flooded forest studied shows a nitrogencycle where inputs and accumulation are maximized when the system is under minimum stress (dry season). During flooding, the system enters a period of dormancy making minimal use of nutrient and energy to avoid or tolerate anaerobiosis.

We studied the relationships between soil nutrient availability and microbial biomass and activity of two contrasting soil conditions in a tropical deciduous forest in western Mexico. Hilltops have higher pH, water, dissolved organic C, and ammonium concentrations than hillslopes. Our main hypothesis was that soil microbial biomass, microbial activity and bacterium species richness would be higher in soils with high availability of nutrients. Fifteen soil cores, 0–5 cm depth, were taken in the dry, early rainy and rainy season, from each of the ten replicate plots in hilltop and hillslope positions located on three contiguous small watersheds. We measured moisture, C, N and P availability, potential C mineralization, net nitrification, microbial biomass and culturable heterotrophic and nitrifying bacteria in composite samples from each plot. Microbial biomass, species richness of culturable heterotrophic bacteria and C mineralization were significantly higher on hilltops than on hillslopes. Net nitrification was, in contrast, significantly higher on hillslopes than on hilltops and counts of culturable nitrifying bacteria were also significantly higher in the rainy-season samples. Hilltops and hillslopes had low similarity in composition of culturable heterotrophic bacterial species, particularly during the rainy season. The results suggested that C and N availability and seasonal changes in soil moisture are important controlling factors for some soil culturable-bacterial species, which may affect both C mineralization and nitrification in these tropical deciduous forest soils.

Formalin (a 33–38% aqueous formaldehyde solution) is currently used for bath treatments to control ectoparasitic infections of fish. Its effects on nitrification were evaluated in a semi-closed pilot scale saltwater recirculating turbot culture system. Tested treatments included 1 h static exposure to 20, 30, 40, 50, 60, 70, 90 mg l−1 formaldehyde without flushing, and long-term (i.e., 2, 4 and 6 h) exposures with constant 60 mg l−1 formaldehyde in a recirculating system. Formaldehyde has no apparent effect on the ammonia oxidative bacterial community. However, a significant effect on nitrite oxidation was observed in 1 h static exposures of concentrations higher than 40 mg l−1, and in recirculating system exposures of 60 mg l−1 formaldehyde for more than 4 h. Repeated treatments may be hazardous for nitrifying bacteria, which could induce an increase in nitrite concentration. Nitrite concentrations should be monitored when treatments are repeated or when they last a long time in recirculating aquaculture systems.

(Accepted 31st July 1999)

In the ‘elfin’ cloud forest of Serrania de Macuira, exchangeable ammonium and nitrate, and the rates of soil nitrogen mineralization and nitrification were measured in soil samples under different water, temperature and mineral nutrient additions. The effects of nitrogen, phosphorus and nitrogen plus phosphorus fertilization on radial trunk growth were measured in three tree species. In the cloud forest soils, concentrations of ammonium were much higher than those of nitrate. Nitrate was higher in samples collected during the afternoon than during the morning, probably as a result of leaching during the night or nitrification during the day. When samples were incubated under different water and temperature treatments, rates of nitrogen mineralization and nitrification increased more with changes in soil water content than with changes in temperature. Nitrification was significantly increased in soils amended with ammonium or with ammonium plus phosphorus, suggesting that nitrification is substrate-limited. Fertilization with nitrogen and phosphorus resulted in significantly increased girth increments in Guapira fragrans (Dum. -Cours.) Little and Rapanea guianensis Aublet. Myrcianthes fragrans (Sw.) D.C. did not respond to the fertilization. The results of this study support the hypothesis that the characteristics of montane rain forest in small and large tropical mountains (the ‘Massenerhebung’ effect) are greatly controlled by soil water conditions and related soil nitrogen availability.

Trois microalgues, Synechocystis (Picocyanobactérie), Chlorella et Micractinium (Chlorophyta) se développant dans le lagunage naturel, ont été mises en culture en milieu axénique et ensemencées dans des microcosmes d'eau usée filtrée, stérilisée ou non. Ceci dans le but d'évaluer les voies d'élimination de NH4, apporté par cette eau usée. L'assimilation algale, la nitrification et le stripping de NH3, se sont révélées les principales voies d'élimination de l'ammonium dans le milieu non stérilisé. Par ailleurs, dans le milieu stérilisé, seuls l'assimilation algale et le stripping sont présents. Les bactéries hétérotrophes aérobies semblent ne pas intervenir dans cette élimination.

Human activity has greatly perturbed the nitrogen cycle through increased fixation by legumes, by energy and fertilizer production, and by the mobilization of N from long-term storage pools. This extra reactive N is readily transported through the environment, and there is increasing evidence that it is changing ecosystems through eutrophication and acidification. Rothamsted Experimental Station, UK has been involved in research on N cycling in ecosystems since its inception in 1843. Measurements of precipitation composition at Rothamsted, made since 1853, show an increase of nitrate and ammonium N in precipitation from 1 and 3 kg N ha−1 yr−1, respectively, in 1855 to a maximum of 8 and 10 kg N ha−1 yr−1 in 1980, decreasing to 4 and 5 kg N ha−1 yr−1 today. Nitrogen inputs via dry deposition do, however, remain high. Recent measurements with diffusion tubes and filter packs show large concentrations of nitrogen dioxide of c. 20 μg m−3 in winter and c. 10 μg m−3 in summer; the difference is linked to the use of central heating, and with variations in wind direction and pollutant source. Concentrations of nitric acid and particulate N exhibit maxima of 1·5 and 2 μg m−3 in summer and winter, respectively. Concentrations of ammonia are small, barely rising above 1 μg m−3.

Taking deposition velocities from the literature gives a total deposition of all measured N species to winter cereals of 43·3 kg N ha−1 yr−1, 84% as oxidized species, 79% dry deposited. The fate of this N deposited to the very long-term Broadbalk Continuous Wheat Experiment at Rothamsted has been simulated using the SUNDIAL N-cycling model: at equilibrium, after 154 yr of the experiment and with N deposition increasing from c. 10 kg ha−1 yr−1 in 1843 to 45 kg ha−1 yr−1 today, c. 5% is leached, 12% is denitrified, 30% immobilized in the soil organic matter and 53% taken off in the crop. The ‘efficiency of use’ of the deposited N decreases, and losses and immobilization increase as the amount of fertilizer N increases. The deposited N itself, and the acidification that is associated with it (from the nitric acid, ammonia and ammonium), has reduced the number of plant species on the 140-yr-old Park Grass hay meadow. It has also reduced methane oxidation rates in soil by c. 15% under arable land and 30% under woodland, and has caused N saturation of local woodland ecosystems: nitrous oxide emission rates of up to 1·4 kg ha−1 yr−1 are equivalent to those from arable land receiving >200 kg N ha−1 yr−1, and in proportion to the excess N deposited; measurements of N cycling processes and pools using 15N pool dilution techniques show a large nitrate pool and enhanced rates of nitrification relative to immobilization. Ratios of gross nitrification[ratio ]gross immobilization might prove to be good indices of N saturation.