Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Nitrogen

  • acid nitrogen
  • amide nitrogen
  • amine nitrogen
  • amino acid nitrogen
  • amino nitrogen
  • ammonia nitrogen
  • assimilable nitrogen
  • atmospheric nitrogen
  • available nitrogen
  • base nitrogen
  • basic nitrogen
  • blood urea nitrogen
  • dry nitrogen
  • endogenous nitrogen
  • fertilizer nitrogen
  • fixed nitrogen
  • foliar nitrogen
  • high nitrogen
  • imine nitrogen
  • inorganic nitrogen
  • kjeldahl nitrogen
  • leaf nitrogen
  • liquid nitrogen
  • mineral nitrogen
  • molecular nitrogen
  • new nitrogen
  • nitrate nitrogen
  • organic nitrogen
  • plant nitrogen
  • pure nitrogen
  • pyridine nitrogen
  • reactive nitrogen
  • serum blood urea nitrogen
  • serum urea nitrogen
  • soil nitrogen
  • soluble nitrogen
  • total ammonia nitrogen
  • total nitrogen
  • total volatile base nitrogen
  • total volatile basic nitrogen
  • urea nitrogen
  • volatile base nitrogen
  • volatile basic nitrogen

  • Terms modified by Nitrogen

  • nitrogen Heterocycle
  • nitrogen Nucleophile
  • nitrogen acquisition
  • nitrogen addition
  • nitrogen adsorption
  • nitrogen allocation
  • nitrogen application
  • nitrogen assimilation
  • nitrogen atmosphere
  • nitrogen atom
  • nitrogen availability
  • nitrogen balance
  • nitrogen base
  • nitrogen bond
  • nitrogen budget
  • nitrogen catabolite repression
  • nitrogen compound
  • nitrogen concentration
  • nitrogen content
  • nitrogen control
  • nitrogen cycle
  • nitrogen cycling
  • nitrogen decreased
  • nitrogen deficiency
  • nitrogen deposition
  • nitrogen dioxide
  • nitrogen donor
  • nitrogen donor atom
  • nitrogen doping
  • nitrogen dynamics
  • nitrogen enrichment
  • nitrogen environment
  • nitrogen excretion
  • nitrogen fertilization
  • nitrogen fertilizer
  • nitrogen fixation
  • nitrogen fixation rate
  • nitrogen flow
  • nitrogen form
  • nitrogen fraction
  • nitrogen gas
  • nitrogen heterocycle
  • nitrogen incorporation
  • nitrogen input
  • nitrogen intake
  • nitrogen intermediate
  • nitrogen inversion
  • nitrogen isotope
  • nitrogen isotope analysis
  • nitrogen isotope composition
  • nitrogen isotope ratio
  • nitrogen level
  • nitrogen ligand
  • nitrogen limitation
  • nitrogen loading
  • nitrogen loss
  • nitrogen metabolism
  • nitrogen metabolite
  • nitrogen mineralization
  • nitrogen monoxide
  • nitrogen mustard
  • nitrogen nucleophile
  • nitrogen oxide
  • nitrogen pollution
  • nitrogen pool
  • nitrogen rate
  • nitrogen ratio
  • nitrogen removal
  • nitrogen requirement
  • nitrogen retention
  • nitrogen solubility
  • nitrogen sorption analysis
  • nitrogen source
  • nitrogen species
  • nitrogen stable isotope
  • nitrogen stable isotope analysis
  • nitrogen starvation
  • nitrogen status
  • nitrogen storage
  • nitrogen stream
  • nitrogen supply
  • nitrogen temperature
  • nitrogen transfer
  • nitrogen treatment
  • nitrogen uptake
  • nitrogen utilization
  • nitrogen value

  • Selected Abstracts


    This work studied the development of free amino acids (FAAs) and dipeptide anserine as quality indices for gutted hake stored in ice for 25 days. The correlation of these compounds was determined with total volatile basic nitrogen (TVBN) which has been used as a quality index, for fish stored in ice. The most abundant free amino acids in hake muscle were found to be threonine, glycine, alanine, glutamic acid, ,-alanine methylhistidine. lysine and the dipeptide, anserine. The only hydrophobic free ammo adds which exhibit significant differences (P<0.05) throughout storage was tryptophan. moreover, this amino acid exhibited a very high correlation (r=0.951) with TVBN. A significant decrease in anserine (P<0.05) correlated with the increases in 1-methylhistidine and ,-alanine throughout storage. These changes also exhibited a very high correlation with TVBN. Therefore, 1-methylhistidine, ,-alanine anserine and tryptophan could be used as quality parameters for hake stored in ice. [source]


    G.B. AWUAH
    ABSTRACT Studies were conducted to investigate the effect of initial container pressure on heat penetration parameters using flexible aluminum containers. A pilot scale liquid nitrogen dispenser, regulated to discharge a fine stream of liquid nitrogen (LN2), provided approximately 10 to 15 psi pressure within the container prior to end-over-end processing in a computer-controlled retort using water immersion with 32 psi over pressure. Thermal process parameters including the heating rate index (fh), lag factor (jh), the cumulative lethality (Fo), cook-value (Co) and the overall heat transfer coefficient (Uo) were examined in relation to retort temperature (241,261F), rpm (0,15 rpm) and product initial temperature (54,121F) using 5% w/w bentonite suspension with or without liquid nitrogen. Generally, containers with added liquid nitrogen had no impact on evaluated data compared to their counterparts without LN2 under similar experimental conditions. Estimated overall heat transfer coefficient (Uo) compared favorably with published data, while the Co/Fo ratio decreased with increasing temperatures as expected. Product cold spot location migrated in either upward or downward direction depending on the mode of heat transfer. Although added LN2 generally had no limiting effect on both heat transfer and heat penetration data, processing aluminum containers with high initial pressure at high retort temperatures could create excessively high internal pressure that could compromise container seam integrity. [source]


    JOURNAL OF PHYCOLOGY, Issue 5 2009
    Espen Granum
    Diel periodicity and effects of inorganic carbon (Ci) and NO3, on the expression of 11 key genes for primary carbon and nitrogen metabolism, including potential C4 photosynthesis, in the marine diatom Thalassiosira pseudonana Hasle et Heimdal were investigated. Target gene transcripts were measured by quantitative reverse transcriptase,PCR, and some of the gene-encoded proteins were analyzed by Western blotting. The diatom was grown with a 12 h photoperiod at two different Ci concentrations maintained by air-equilibration with either 380 ,L · L,1 (near-ambient) or 100 ,L · L,1 (low) CO2. Transcripts of the principal Ci and NO3, assimilatory genes RUBISCO LSU (rbcL) and nitrate reductase displayed very strong diel oscillations with peaks at the end of the scotophase. Considerable diel periodicities were also exhibited by the ,-carboxylase genes phosphoenolpyruvate carboxylase (PEPC1 and PEPC2) and phosphoenolpyruvate carboxykinase (PEPCK), and the Benson,Calvin cycle gene sedoheptulose,bisphosphatase (SBPase), with peaks during mid- to late scotophase. In accordance with the transcripts, there were substantial diel periodicities in PEPC1, PEPC2, PEPCK, and especially rbcL proteins, although they peaked during early to mid-photophase. Inorganic carbon had some transient effects on the ,-carboxylase transcripts, and glycine decarboxylase P subunit was highly up-regulated by low Ci concentration, indicating increased capacity for photorespiration. Nitrogen-starved cells had reduced amounts of carbon metabolic gene transcripts, but the PEPC1, PEPC2, PEPCK, and rbcL transcripts increased rapidly when NO3, was replenished. The results suggest that the ,-carboxylases in T. pseudonana play key anaplerotic roles but show no clear support for C4 photosynthesis. [source]


    JOURNAL OF PHYCOLOGY, Issue 3 2006
    Anna Christina Tyler
    Macroalgae, often the dominant primary producers in shallow estuaries, can be important regulators of nitrogen (N) cycling. Like phytoplankton, actively growing macroalgae release N to the water column; yet little is known about the quantity or nature of this release. Using 15N labeling in laboratory and field experiments, we estimated the quantity of N released relative to assimilation and gross uptake by Gracilaria vermiculophylla (Ohmi) Papenfuss (Rhodophyta, Gracilariales), a non-native macroalgae. Field experiments were carried out in Hog Island Bay, a shallow back-barrier lagoon on the Virginia coast where G. vermiculophylla makes up 85%,90% of the biomass. There was good agreement between laboratory and field measurements of N uptake and release. Daily N assimilation in field experiments (32.3±7.2 ,mol N·g dw,1·d,1) was correlated with seasonal and local N availability. The average rate of N release across all sites and dates (65.8±11.6 ,mol N·g dw,1·d,1) was 67% of gross daily uptake, and also varied among sites and seasons (range=33%,99%). Release was highest when growth rates and nutrient availability were low, possibly due to senescence during these periods. During summer biomass peaks, estimated N release from macroalgal mats was as high as 17 mmol N·m,2·d,1. Our results suggest that most estimates of macroalgal N uptake severely underestimate gross N uptake and that N is taken up, transformed, and released to the water column on short time scales (minutes,hours). [source]


    JOURNAL OF PHYCOLOGY, Issue 3 2004
    Kazuyoshi Kuwano
    The gametophytic cells of six species of Laminariales, Laminaria japonica Areschoug, L. longissima Miyabe, Kjellmaniella crassifolia Miyabe, Ecklonia stolonifera Okamura, E. kurome Okamura, and Undaria pinnatifida (Harvey) Suringar, were subjected to cryopreservation in liquid nitrogen. The cells were suspended in various cryoprotective solutions and slowly cooled to ,40°C over a period of 4 h. After this slow cooling step, the suspensions were immediately immersed in liquid nitrogen. All the species of Laminariaceae used in the present study survived maximally in a mixture of ethylene glycol and proline. On the other hand, the gametophytic cells of Undaria pinnatifida, a member of the Alariaceae, survived maximally in the mixture of glycerol and proline. The viability of the thawed gametophytic cells decreased during postthawing incubation. The decrease in viability continued for 4,6 days, and the minimum levels ranged from 36.2% to 67.2%. After 4,6 days of incubation, the percentage viability of all strains began to increase due to the renewal of cell division. [source]


    JOURNAL OF PHYCOLOGY, Issue 5 2002
    Pascal Claquin
    The elemental composition and the cell cycle stages of the marine diatom Thalassiosira pseudonana Hasle and Heimdal were studied in continuous cultures over a range of different light- (E), nitrogen- (N), and phosphorus- (P) limited growth rates. In all growth conditions investigated, the decrease in the growth rate was linked with a higher relative contribution of the G2+M phase. The other phases of the cell cycle, G1 and S, showed different patterns, depending on the type of limitation. All experiments showed a highly significant increase in the amount of biogenic silica per cell and per cell surface with decreasing growth rates. At low growth rates, the G2+M elongation allowed an increase of the silicification of the cells. This pattern could be explained by the major uptake of silicon during the G2+M phase and by the independence of this process on the requirements of the other elements. This was illustrated by the elemental ratios Si/C and Si/N that increased from 2- to 6-fold, depending of the type of limitation, whereas the C/N ratio decreased by 10% (E limitation) or increased by 50% (P limitation). The variations of the ratios clearly demonstrate the uncoupling of the Si metabolism compared with the C and N metabolisms. This uncoupling enabled us to explain that in any of the growth condition investigated, the silicification of the cells increased at low growth rates, whereas carbon and nitrogen cellular content are differently regulated, depending of the growth conditions. [source]


    Hanisak M. D.
    This study used the tremendous biochemical and ecological diversity of macroalgae to assess nitrogen and phosphorus availability at a broad, ecosystem-level scale in the Florida Keys and nearby waters. Spatial variation in tissue nutrients (carbon, C; nitrogen, N; phosphorus, P) of dominant macroalgae were assessed, both as ratios and absolute values, along 12 inshore-offshore transects in the Florida Keys and at 10 stations in nearby Florida Bay. The resulting detailed analysis demonstrated spatial and temporal patterns in macroalgal tissue nutrients. The transect data revealed no universal inshore-offshore patterns in tissue nutrients and no obvious "hotspots" of nutrient enrichment. Similarly, when data were compared among segments, there was no universal geographical pattern in tissue nutrients for all species. The most striking result was that the N and P status of macroalgae in Florida Bay was significantly different than other locations. Macroalgae collected from Florida Bay generally had higher N and lower P levels than algae collected elsewhere. The most common inshore-offshore pattern was higher %N and lower %P availability inshore; however, limited inshore-offshore differences in N:P ratio suggests that both nutrients were generally readily available in proportional amounts required by the various species. Most species in this study had higher %N, and to a lesser extent, higher %P and %C in March than in July. Based on the published literature on other species of macroalgae, it appears that N and P are generally available in sufficient quantities that most macroalgal growth is not limited by either nutrient. [source]

    Drug design: hiding in full view

    Norman S. Radin
    Abstract Compounds that can produce potent biological effects in cells encompass a variety of structural motifs. Many of these compounds share a structural feature that has rarely been noted. It is an allylic cluster of atoms, a 3-carbon chain with a double bond between two of the atoms and an oxygen atom at the other end. The oxygen can be in a hydroxyl group, or in an ether or ketal or ester linkage, or simply a carbonyl form. In the latter case, the linkage is an allylic ketone (ene-one) structure. Nitrogen is often seen in equivalent forms. Inclusion of at least one allylic moiety appears to be able to turn a modestly active or inert compound into an effective drug or toxin. Some compounds lack the allylic moiety but develop one by enzymatic action, usually via cytochrome P-450 enzymes. These metabolites probably represent the active drug forms. The above concepts seem to be radically simplistic and improbable, but the evidence supporting them and the explanations for the biological activities are hidden "in plain view." Comparisons with the pleiotropic activities of the allylic sphingolipid, ceramide, indicate that many allylic drugs operate by controlling the state of protein phosphorylation, by activating proteases, by generating reactive oxygen species, by slowing mitochondrial electron transport, or by lowering cellular glutathione concentrations. Drug Dev Res 69:15,25, 2008 © 2008 Wiley-Liss, Inc. [source]

    Caste-specific N and C isotope ratios in fungus-growing termites with special reference to uric acid preservation and their nutritional interpretation

    I. Tayasu
    Abstract 1. Nitrogen and carbon isotope ratios and uric acid concentrations in fungus-growing termites (Isoptera: Termitidae: Macrotermitinae), sampled in Cameroon and Thailand, were determined in order to compare castes that are known to differ in behaviour and feeding habits. 2. Nitrogen isotope ratios (,15N) were either not significantly changed or lower in workers compared with the diet (the fungus combs), whereas carbon isotope ratios (,13C) were higher in worker termites than in the fungus combs. 3. In old workers, ,15N values were unexpectedly low and correlated negatively with whole-body uric acid concentrations. This indicates that older workers retain uric acid, which has a low ,15N value, to conserve nitrogen within the colony and, furthermore, that older colony members may ultimately be consumed by younger conspecifics. [source]

    Effect of Platinum and Ruthenium Incorporation on Voltammetric Behavior of Nitrogen Doped Diamond-Like Carbon Thin Films

    ELECTROANALYSIS, Issue 23 2009
    W. Khun
    Abstract Nitrogen doped diamond-like carbon thin films with or without platinum and ruthenium incorporation (N-DLC or PtRuN-DLC) were deposited on highly conductive p-Si substrates by DC magnetron sputtering to study the effect of Pt and Ru doping on the voltammetric performance of the N-DLC films. The potential windows of these film electrodes were measured in different electrolytic solutions, such as H2SO4, HCl and KCl. The cyclic voltammograms obtained from the N-DLC film electrodes in these solutions showed wide potential windows while the introduction of Pt and Ru into the film electrodes apparently narrowed down the potential windows due to their catalytic activities. [source]

    An Efficient Molybdenum(VI)-Catalyzed Direct Substitution of Allylic Alcohols with Nitrogen, Oxygen, and Carbon Nucleophiles

    Hongwei Yang
    Abstract Direct nucleophilic substitution of allylic alcohols with various nitrogen, oxygen, and carbon nucleophiles catalyzed by MoO2(acac)2 was realized. The corresponding products were obtained in moderate-to-excellent yields. Studies of the reaction mechanism showed that a carbenium intermediate was formed in the transition state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    The Combination of TsNH2 and NCS as Nitrogen and Chlorine Sources for Direct Diamination of Enones

    Cody Timmons
    Abstract The regio-, stereo-, and chemoselective diamination of enones has been achieved without the observation of any haloamines. The reaction employs the readily available inexpensive combination of NCS and TsNH2 as an electrophilic nitrogen source, and three nitriles as nucleophilic nitrogen sources. A novel mechanism involving the formation of aziridinium intermediates from the reaction of TsNHCl with olefins and a new [2+3] cyclic addition for aziridinim ring opening has been proposed for the electrophilic diamination of olefins. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Comparison of greenhouse gas fluxes and nitrogen budgets from an ombotrophic bog in Scotland and a minerotrophic sedge fen in Finland

    J. Drewer
    Northern peatlands cover approximately 4% of the global land surface area. Those peatlands will be particularly vulnerable to environmental and climate change and therefore it is important to investigate their total greenhouse gas (GHG) budgets, to determine the feedback on the climate. Nitrogen (N) is known to influence the GHG budget in particular by affecting the methane (CH4) balance. At two peatland sites in Scotland and Finland GHG fluxes of carbon dioxide (CO2), methane and nitrous oxide (N2O) and nitrogen fluxes were measured as part of the European project ,NitroEurope'. The Scottish site, Auchencorth Moss, was a GHG sink of ,321, ,490 and ,321 g CO2 eq m,2 year,1 in 2006, 2007 and 2008, respectively, with CO2 as the dominating GHG. In contrast, the dominating GHG at the Finnish site, Lompolojänkkä, was CH4, resulting in the site being a net GHG source of +485 and +431 g CO2 eq m,2 year,1 in 2006 and 2007, respectively. Therefore, Auchencorth Moss had a negative global warming potential (GWP) whilst Lompolojänkkä had a positive GWP over the investigated time period. Initial results yielded a positive N budget for Lompolojänkkä of 7.1 kg N ha,1 year,1, meaning the site was gaining nitrogen, and a negative N budget for Auchencorth Moss of ,2.4 kg N ha year,1, meaning the site was losing nitrogen. [source]

    Graphene-Based Nanoporous Materials Assembled by Mediation of Polyoxometalate Nanoparticles

    Ding Zhou
    Abstract A kind of graphene-based nanoporous material is prepared through assembling graphene sheets mediated through polyoxometalate nanoparticles. Owing to the strong interaction between graphene and polyoxometalate, 2D graphene sheets with honeycomb-latticed carbon atoms could assemble into a porous structure, in which 3D polyoxometalate nanoparticles serve as the crosslinkers. Nitrogen and hydrogen sorption analysis reveal that the as-prepared graphene-based hybrid material possesses a specific surface area of 680 m2 g,1 and a hydrogen uptake volume of 0.8,1.3 wt%. Infrared spectrometry is used to probe the electron density changes of polyoxometalate particle in the redox-cycle and to verify the interaction between graphene and polyoxometalate. The as-prepared graphene-based materials are further characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. [source]

    Balances of phosphorus and nitrogen in carp ponds

    R. Knösche
    The impact of carp pond effluents on natural waters was investigated in the German federal states of Brandenburg, Saxony and Bavaria, and in Hungary. Data from 38 ponds (size = 0.25,122 ha) were available for the calculation of inlet,outlet differences. An average difference of 0.51 kg phosphorus (P) ha,1 year,1 was obtained. This means that every hectare of pond surface releases 510 g P less than it receives from the incoming water. This result was independent of the amount of fish harvested (, 1500 ha,1 year,1). The average retention of P (P-balance) was 5.71 kg P ha,1 year,1. Phosphorus retention increased with increasing intensity of production. Nitrogen (N) retention increased with production intensity from 78.5 kg ha,1 year,1 in German standard ponds to >,290 kg N ha,1 year,1in pig-cum-fish ponds in Hungary. A predominantly mineralized sludge suspension is released during harvesting at loads below 1% of the retention capacity of the pond. Under usual pond management regimes, the sludge load during harvesting ranged from 50 to 200 L ha,1, equivalent to 0.3,9.3 g dry matter ha,1. The present study suggests that ponds are not a burden on the environment. By contrast, these water bodies improve water quality. Therefore, pressures to reduce the intensity of pond production cannot be justified on the basis of supposed impacts on water quality. However, even if loads during harvesting are low compared with the retention capacity of the pond, more effort should be carried out to reduce the pollution of streams by pond outlets downstream. This can be done by limiting pond drainage to periods when the suspended material has settled or by short-term sedimentation of the sludge in a settling pond downstream of the rearing facility. [source]

    Seasonal response of nutrients to reduced phosphorus loading in 12 Danish lakes

    FRESHWATER BIOLOGY, Issue 10 2005
    Summary 1.,Concentrations of phosphorus, nitrogen and silica and alkalinity were monitored in eight shallow and four deep Danish lakes for 13 years following a phosphorus loading reduction. The aim was to elucidate the seasonal changes in nutrient concentrations during recovery. Samples were taken biweekly during summer and monthly during winter. 2.,Overall, the most substantive changes in lake water concentrations were seen in the early phase of recovery. However, phosphorus continued to decline during summer as long as 10 years after the loading reduction, indicating a significant, albeit slow, decline in internal loading. 3.,Shallow and deep lakes responded differently to reduced loading. In shallow lakes the internal phosphorus release declined significantly in spring, early summer and autumn, and only non-significantly so in July and August. In contrast, in deep lakes the largest reduction occurred from May to August. This difference may reflect the much stronger benthic pelagic-coupling and the lack of stratification in shallow lakes. 4.,Nitrogen only showed minor changes during the recovery period, while alkalinity increased in late summer, probably conditioned by the reduced primary production, as also indicated by the lower pH. Silica tended to decline in winter and spring during the study period, probably reflecting a reduced release of silica from the sediment because of enhanced uptake by benthic diatoms following the improved water transparency. 5.,These results clearly indicate that internal loading of phosphorus can delay lake recovery for many years after phosphorus loading reduction, and that lake morphometry (i.e. deep versus shallow basins) influences the patterns of change in nutrient concentrations on both a seasonal and interannual basis. [source]

    Does high nitrogen loading prevent clear-water conditions in shallow lakes at moderately high phosphorus concentrations?

    FRESHWATER BIOLOGY, Issue 1 2005
    María A. González Sagrario
    Summary 1. The effect of total nitrogen (TN) and phosphorus (TP) loading on trophic structure and water clarity was studied during summer in 24 field enclosures fixed in, and kept open to, the sediment in a shallow lake. The experiment involved a control treatment and five treatments to which nutrients were added: (i) high phosphorus, (ii) moderate nitrogen, (iii) high nitrogen, (iv) high phosphorus and moderate nitrogen and (v) high phosphorus and high nitrogen. To reduce zooplankton grazers, 1+ fish (Perca fluviatilis L.) were stocked in all enclosures at a density of 3.7 individuals m,2. 2. With the addition of phosphorus, chlorophyll a and the total biovolume of phytoplankton rose significantly at moderate and high nitrogen. Cyanobacteria or chlorophytes dominated in all enclosures to which we added phosphorus as well as in the high nitrogen treatment, while cryptophytes dominated in the moderate nitrogen enclosures and the controls. 3. At the end of the experiment, the biomass of the submerged macrophytes Elodea canadensis and Potamogeton sp. was significantly lower in the dual treatments (TN, TP) than in single nutrient treatments and controls and the water clarity declined. The shift to a turbid state with low plant coverage occurred at TN >2 mg N L,1 and TP >0.13,0.2 mg P L,1. These results concur with a survey of Danish shallow lakes, showing that high macrophyte coverage occurred only when summer mean TN was below 2 mg N L,1, irrespective of the concentration of TP, which ranged between 0.03 and 1.2 mg P L,1. 4. Zooplankton biomass and the zooplankton : phytoplankton biomass ratio, and probably also the grazing pressure on phytoplankton, remained overall low in all treatments, reflecting the high fish abundance chosen for the experiment. We saw no response to nutrition addition in total zooplankton biomass, indicating that the loss of plants and a shift to the turbid state did not result from changes in zooplankton grazing. Shading by phytoplankton and periphyton was probably the key factor. 5. Nitrogen may play a far more important role than previously appreciated in the loss of submerged macrophytes at increased nutrient loading and for the delay in the re-establishment of the nutrient loading reduction. We cannot yet specify, however, a threshold value for N that would cause a shift to a turbid state as it may vary with fish density and climatic conditions. However, the focus should be widened to use control of both N and P in the restoration of eutrophic shallow lakes. [source]

    Laser Ablation (193 nm), Purification and Determination of Very Low Concentrations of Solar Wind Nitrogen Implanted in Targets from the GENESIS Spacecraft

    Laurent Zimmermann
    azote; ablation laser; purification; spectrométrie de masse; mission GENESIS The GENESIS space mission recovered ions emitted by the Sun during a 27 month period. In order to extract, purify and determine the very low quantities of solar nitrogen implanted in the GENESIS targets, a new installation was developed and constructed at the CRPG (Nancy, France). It permitted the simultaneous determination of nitrogen and noble gases extracted from the target by laser ablation. The extraction procedure used a 193 nm excimer laser that allowed for surface contamination in the outer 5 nm to be removed, followed by a step that removed 50 nm of the target material, extracting the solar nitrogen and noble gases implanted in the target. Following purification using Ti and Zr getters for noble gases and a Cu-CuO oxidation cycle for N2, the extracted gases were analysed by static mode (pumps closed) mass spectrometry using electron multiplier and Faraday cup detectors. The nitrogen blanks from the purification section and the static line (30 minutes) were only 0.46 picomole and 0.47 picomole, respectively. La mission GENESIS a récupéré des ions émis par le soleil pendant une période de 27 mois. Afin d'extraire, purifier et analyser de très faibles quantités d'azote solaire implantés dans des cibles GENESIS, une nouvelle installation a été développée et construite au CRPG. Elle a permis l'analyse simultanée de l'azote et des gaz nobles extraits de la couche d'or par ablation. La procédure d'extraction a utilisé un laser Excimer 193 nm qui a permis une étape d'extraction à 5 nm pour éliminer la pollution à la surface, suivie d'une étape qui a extrait jusqu'à une profondeur de 50 nm l'azote et les gaz rares solaires implantés dans la cible. Après une purification à l'aide de getters Ti et Zr pour les gaz rares et un cycle d'oxydation Cu-CuO pour N2, les gaz extraits ont été analysés en mode statique (pompage fermé) par spectrométrie de masse à l'aide d'un multiplicateur d'électrons et d'une cage de Faraday. Les blancs d'azote provenant de la partie purification et de la ligne en statique (30 minutes) étaient de seulement 0.46 et 0.47 picomole, respectivement. [source]

    Nitrogen and the Colour of the Crops

    GERMAN RESEARCH, Issue 2-3 2002
    Hermann J. Heege Prof. em.
    To each plant its due: An optical sensor on the fertiliser distributor uses leaf colouring to determine the corn's nitrogen requirement. This restricts fertilisation to actual requirements [source]

    The response of heterotrophic activity and carbon cycling to nitrogen additions and warming in two tropical soils

    Abstract Nitrogen (N) deposition is projected to increase significantly in tropical regions in the coming decades, where changes in climate are also expected. Additional N and warming each have the potential to alter soil carbon (C) storage via changes in microbial activity and decomposition, but little is known about the combined effects of these global change factors in tropical ecosystems. In this study, we used controlled laboratory incubations of soils from a long-term N fertilization experiment to explore the sensitivity of soil C to increased N in two N-rich tropical forests. We found that fertilization corresponded to significant increases in bulk soil C concentrations, and decreases in C loss via heterotrophic respiration (P< 0.05). The increase in soil C was not uniform among C pools, however. The active soil C pool decomposed faster with fertilization, while slowly cycling C pools had longer turnover times. These changes in soil C cycling with N additions corresponded to the responses of two groups of microbial extracellular enzymes. Smaller active C pools corresponded to increased hydrolytic enzyme activities; longer turnover times of the slowly cycling C pool corresponded to reduced activity of oxidative enzymes, which degrade more complex C compounds, in fertilized soils. Warming increased soil respiration overall, and N fertilization significantly increased the temperature sensitivity of slowly cycling C pools in both forests. In the lower elevation forest, respired CO2 from fertilized cores had significantly higher ,14C values than control soils, indicating losses of relatively older soil C. These results indicate that soil C storage is sensitive to both N deposition and warming in N-rich tropical soils, with interacting effects of these two global change factors. N deposition has the potential to increase total soil C stocks in tropical forests, but the long-term stability of this added C will likely depend on future changes in temperature. [source]

    Tradeoffs and thresholds in the effects of nitrogen addition on biodiversity and ecosystem functioning: evidence from inner Mongolia Grasslands

    Abstract Nitrogen (N) deposition is widely considered an environmental problem that leads to biodiversity loss and reduced ecosystem resilience; but, N fertilization has also been used as a management tool for enhancing primary production and ground cover, thereby promoting the restoration of degraded lands. However, empirical evaluation of these contrasting impacts is lacking. We tested the dual effects of N enrichment on biodiversity and ecosystem functioning at different organizational levels (i.e., plant species, functional groups, and community) by adding N at 0, 1.75, 5.25, 10.5, 17.5, and 28.0 g N m,2 yr,1 for four years in two contrasting field sites in Inner Mongolia: an undisturbed mature grassland and a nearby degraded grassland of the same type. N addition had both quantitatively and qualitatively different effects on the two communities. In the mature community, N addition led to a large reduction in species richness, accompanied by increased dominance of early successional annuals and loss of perennial grasses and forbs at all N input rates. In the degraded community, however, N addition increased the productivity and dominance of perennial rhizomatous grasses, with only a slight reduction in species richness and no significant change in annual abundance. The mature grassland was much more sensitive to N-induced changes in community structure, likely as a result of higher soil moisture accentuating limitation by N alone. Our findings suggest that the critical threshold for N-induced species loss to mature Eurasian grasslands is below 1.75 g N m,2 yr,1, and that changes in aboveground biomass, species richness, and plant functional group composition to both mature and degraded ecosystems saturate at N addition rates of approximately 10.5 g N m,2 yr,1. This work highlights the tradeoffs that exist in assessing the total impact of N deposition on ecosystem function. [source]

    Combined Effect of Nitrogen- and Oxygen-Containing Functional Groups of Microporous Activated Carbon on its Electrochemical Performance in Supercapacitors

    Denisa Hulicova-Jurcakova
    Abstract Microporous activated carbon originating from coconut shell, as received or oxidized with nitric acid, is treated with melamine and urea and heated to 950,°C in an inert atmosphere to modify the carbon surface with nitrogen- and oxygen-containing groups for a systematic investigation of their combined effect on electrochemical performance in 1,M H2SO4 supercapacitors. The chemistry of the samples is characterized using elemental analysis, Boehm titration, potentiometric titration, and X-ray photoelectron spectroscopy. Sorption of nitrogen and carbon dioxide is used to determine the textural properties. The results show that the surface chemistry is affected by the type of nitrogen precursor and the specific groups present on the surface before the treatment leading to the incorporation of nitrogen. Analysis of the electrochemical behavior of urea- and melamine-treated samples reveal pseudocapacitance from both the oxygen and the nitrogen containing functional groups located in the pores larger than 10,Å. On the other hand, pores between 5,Å and 6,Å are most effective in a double-layer formation, which correlates well with the size of hydrated ions. Although the quaternary and pyridinic-N-oxides nitrogen groups have enhancing effects on capacitance due to the positive charge, and thus an improved electron transfer at high current loads, the most important functional groups affecting energy storage performance are pyrrolic and pyridinic nitrogen along with quinone oxygen. [source]

    A comparative study on low-energy elastic electron-NHx (x = 1,2,3) collisions

    L. M. Brescansin
    Abstract In this work, a theoretical study on elastic electron-NHx (x = 1,2,3) collisions in the low-energy range is presented. More specifically, calculated elastic differential, integral, and momentum transfer cross-sections are reported in the (1,30)-eV energy range. An optical potential composed of static, exchange, and correlation,polarization contributions is used to represent the electron-target interaction whereas the iterative Schwinger variational method and the method of continued fractions are used to solve the scattering equations. Comparison of the calculated cross-sections for electron scattering by these targets shows that the results are very similar to each other at higher incident energies. This similarity indicates that the interaction between the scattering electron and the central Nitrogen is dominant. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

    The Ratios of Carbon, Nitrogen, and Phosphorus in a Wetland Coastal Ecosystem of Southern India

    Lizen Mathews
    Abstract The fertility of the coastal and estuarine waters is of great concern because of its influence on the productivity of these waters. Seasonal variations in the distribution of organic carbon, total nitrogen and total phosphorus in the sediments of Kuttanad Waters, a part of the tropical Cochin Estuary on the south west coast of India, are examined to identify the contribution of sediments to the fertility of the aquatic systems. The adjoining region has considerable agricultural activity. The fresh water zones had higher quantities of silt and clay whereas the estuarine zone was more sandy. Organic carbon, total phosphorus and total nitrogen were higher in the fresh water zones and lower in the estuarine zones. Total phosphorus and organic carbon showed the lowest values during monsoon periods. No significant trends were observed in the seasonal distributions of total nitrogen. Ratios of C/N, C/P and N/P, and the phosphorus and nitrogen content indicate significant modification in the character of the organic matter. Substantial amounts of the organic matter can contribute to reducing conditions and modify diagenetic processes. [source]

    Comparative Effect of Nitrogen Sources on Maize under Saline and Non-saline Conditions

    M. Irshad
    Abstract The main objective of this study was to compare the relationship between biomass yield and nutrient uptake in salt-stressed maize (Zea mays L.) following nitrogen (N) nutrition in a greenhouse. Three forms of N were applied, each at the rate of 100 kg ha,1: urea-N, nitrate-N, 1/2 urea-N + 1/2 nitrate-N (mixed-N) and no N application (control). Maize was grown as a test crop for 6 weeks. All N sources greatly stimulated crop growth and nutrient uptake compared with the control. The biomass (shoot and root) of maize was significantly greater in mixed-N treatment than in single sources in saline soil whereas it varied in the order of urea-N > mixed-N > nitrate-N > control in non-saline soil. Under both soil conditions, the concentration of Ca, Mg and Na in shoot was highest in nitrate-N treatments while that of K was highest in the control. Shoot nitrogen concentration was not significantly different among N sources under non-saline treatment, whereas under saline conditions, the concentration varied markedly in the order of nitrate-N > urea-N > mixed-N > control. The mineral concentrations in the shoot increased under salt treated soil when compared with non-saline soil. The ratios of Na/K, Na/Ca and Na/Mg were also higher under salt stress due to higher accumulation of Na ion in the shoot. Among N-fertilizer sources, Na/Ca and Na/Mg ratios were highest in control whereas Na/K ratio was the highest in nitrate-N treatment. The lowest cation ratios were noted in mixed-N-treated plants under both soils. Regression analysis showed that maize biomass was related to N concentration by the following equations: Y = ,4.54 + 0.97N for the non-saline soil and Y = 0.89 + 0.25N for the saline soil. Nitrogen use efficiency for non-saline soil exceeded that of saline soil by 15 %. [source]

    Nitrogen, Phosphorus, Potassium, Magnesium and Calcium Removal by Brown Midrib Sorghum Sudangrass in the Northeastern USA

    Q. M. Ketterings
    Abstract For the long-term sustainability of the dairy industry in the Northeastern USA, manure nutrient application rates should not exceed crop nutrient removal once above-optimum soil fertility levels are reached. Dairy producers have shown a growing interest in brown midrib (BMR) forage sorghum (Sorghum bicolor (L.) Moench.) × sudangrass (Sorghum sudanense Piper) hybrids (S × S) as a more environmentally sound alternative to maize (Zea mays L.) but data on S × S nutrient removal rates are scant. Our objectives were to determine N, P, K, Ca and Mg removal with harvest as impacted by N application rate, using six N rate studies in New York. One of the six sites had a recent manure history. Although site-to-site differences existed, N application tended to decrease P and K and increase N, Ca and Mg concentrations in BMR S × S forage. Nutrient removal and yield were highly correlated for all sites except one location that showed a K deficiency. The crop removed large amounts of P and K in the manured site, suggesting that BMR S × S is an excellent scavenger of these nutrients. If manure is applied mid-season, forage K levels are likely too high for feeding to non-lactating cows. [source]

    Effect of N Fertilization Rate on Sugar Yield and Non-Sugar Impurities of Sugar Beets (Beta vulgaris) Grown Under Mediterranean Conditions

    J. T. Tsialtas
    Abstract For three successive growing seasons (1999,2001), a completely randomized block design experiment was established at the surrounding area of each of four sugar beet processing plants of Hellenic Sugar Industry SA, Greece (a total of 12 experiments). Nitrogen was applied at five rates (0, 60, 120, 180 and 240 kg N ha,1) and six replications per rate. Nitrogen fertilization had site-specific effects on quantitative (fresh root and sugar yields) and qualitative (sucrose content, K, Na, , -amino N) traits. When data were combined over years and sites, fresh root and sugar yields were maximized at high N rates (330.75 and 295 kg N ha,1 respectively), as derived from quadratic functions fitted to data. In three trials, increased N rates had negative effects on root and sugar yield. These sites were characterized by high yield in control plots, light soil texture (sand > 50 %) and low CEC values. When data were converted into relative values (the ratio of the trait values to the control mean of each experiment), root and sugar yield was found to be maximized at higher N rates (350 and 316 kg N ha,1, respectively). Sucrose content was strongly and linearly reduced by the increased N rates when data were combined but a significant reduction with increasing N rates was found in only two sites. Non-sugar impurities (K, Na, , -amino N) were positively related to the increased N rates when data were combined. Sodium and , -amino N showed to be most affected by N fertilization as positive relationships were found in six and eight of 12 locations, respectively. Increased N supply resulted in higher soil NO3 -N concentrations (0,90 cm depth) at harvest which were related with amino N contents in sugar beet roots (in 1999 and 2001). [source]

    Strategies to Improve the Use Efficiency of Mineral Fertilizer Nitrogen Applied to Winter Wheat

    K. Blankenau
    Recovery of fertilizer nitrogen (N) applied to winter wheat crops at tillering in spring is lower than that of N applied at later growth stages because of higher losses and immobilization of N. Two strategies to reduce early N losses and N immobilization and to increase N availability for winter wheat, which should result in an improved N use efficiency (= higher N uptake and/or increased yield per unit fertilizer N), were evaluated. First, 16 winter wheat trials (eight sites in each of 1996 and 1997) were conducted to investigate the effects of reduced and increased N application rates at tillering and stem elongation, respectively, on yield and N uptake of grain. In treatment 90-70-60 (90 kg N ha,1 at tillering, 70 kg N ha,1 at stem elongation and 60 kg N ha,1 at ear emergence), the average values for grain yield and grain N removal were up to 3.1 and 5.0 % higher than in treatment 120-40-60, reflecting conventional fertilizer practice. Higher grain N removal for the treatment with reduced N rates at tillering, 90-70-60, was attributed to lower N immobilization (and N losses), which increased fertilizer N availability. Secondly, as microorganisms prefer NH4+ to NO3, for N immobilization, higher net N immobilization would be expected after application of the ammonium-N form. In a pot experiment, net N immobilization was higher and dry matter yields and crop N contents at harvest were lower with ammonium (ammonium sulphate + nitrification inhibitor Dicyandiamide) than with nitrate (calcium nitrate) nutrition. Five field trials were then conducted to compare calcium nitrate (CN) and calcium ammonium nitrate (CAN) nutrition at tillering, followed by two CAN applications for both treatments. At harvest, crop N and grain yield were higher in the CN than in the CAN treatment at each N supply level. In conclusion, fertilizer N use efficiency in winter wheat can be improved if N availability to the crops is increased as a result of reduced N immobilization (and N losses) early in the growth period. N application systems could be modified towards strategies with lower N applications at tillering compensated by higher N dressing applications later. An additional advantage is expected to result from use of nitrate-N fertilizers at tillering. Strategien zur Verbesserung der Effizienz von Düngerstickstoff in Winterweizen Aus früheren Versuchen mit Winterweizen ist bekannt, daß zur Ernte die Wiederfindung von im Frühjahr zur Bestokkung gedüngtem Stickstoff (N) geringer ist, als die von N aus Spätgaben. Die Ursachen liegen in einer höheren mikrobiell-bedingten Netto-N-Immobilisation, aber auch N-Verlusten zwischen Bestockung und Schoßbeginn im Vergleich zu späteren Wachstumstadien begründet. In den vorliegenden Versuchen wurden zwei Strategien getestet, um insbesondere die früh in der Vegetation auftretende Netto-N-Immobilisation zu vermindern. Die dadurch erwartete erhöhte N-Verfügbarkeit sollte zu einer erhöhten N-Effizienz (höherer N-Entzug/Ertrag bezogen auf die N-Düngung) führen. 1996 und 1997 wurden jeweils 8 Feldversuche mit Winterweizen durchgeführt, um den Einfluß einer reduzierten Andüngung bei gleichzeitig erhöhter Schossergabe im Vergleich zur konventionellen N-Düngung zu untersuchen. Tatsächlich wurden in dem Prüfglied 90-70-60 (N-Sollwertdüngung: 90 kg N ha,1, Schossergabe: 70 kg N ha,1, Ährengabe: 60 kg N ha,1) im Mittel bis zu 3.1 % höhere Erträge und 5.0 % höhere N-Abfuhren mit dem Korn im Vergleich zur konventionellen Variante 120-40-60 (N-Sollwertdüngung: 120 kg N ha,1, Schossergabe: 40 kg N ha,1 und Ährengabe: 60 kg N ha,1) erzielt. Die höhere N-Abfuhr kann auf eine erhöhte N-Verfügbarkeit infolge geringerer mikrobieller N-Festlegung zurückgeführt werden. Da die vornehmlich heterotrophen Bodenmikroorganismen bevorzugt NH4+ gegenüber NO3, immobilisieren, kann eine höhere N-Immobilisation bei Ammonium-Düngung erwartet werden. Tatsächlich wurden in einem Gefäßversuch nach Düngung von Ammoniumsulfat (+ Nitrifikationshemmer Dicyandiamid) geringere Trokkenmasseerträge und N-Aufnahmen von Weizenpflanzen erzielt als mit Calciumnitrat. Für die Ammoniumsulfatvariante ergab sich eine höhere Netto-N-Immobilisation. Danach wurde in fünf Feldversuchen mit Winterweizen der Einfluß einer Andüngung mit Nitrat (Calciumnitrat) im Vergleich zur Verwendung des ammoniumhaltigen Kalkammonsalpeters (KAS) auf die N-Aufnahme und den Kornertrag untersucht (beide Varianten erhielten KAS als Spätgaben). In der nitratangedüngten Variante wurden zum Teil signifikant höhere Ertäge und N-Aufnahmen in Korn und Stroh ermittelt. Aus den dargestellten Versuchen kann gefolgert werden, daß die Düngerstickstoff-Effizienz verbessert werden kann, wenn vor allem die N-Immobilisation (und eventuell auch N-Verluste) in frühen Wachstumsstadien zwischen Bestockung und Schoßbeginn verringert und so die N-Verfügbarkeit erhöht wird. Es kann empfohlen werden Winterweizenbestände mit geringeren N-Mengen , als nach N-Sollwert 120 kg N ha,1 vorgesehen , anzudüngen und die Schossergabe entsprechend zu erhöhen. Die Verwendung von nitrathaltigen Düngern bei der Andüngung ist von Vorteil. [source]

    Effects of Nitrogen on Dry Matter Accumulation and Productivity of Three Cropping Systems and Residual Effects on Wheat in Deep Vertisols of Central India

    P. Ramesh
    A field experiment was conducted on deep vertisols of Bhopal, India to study the effects of three levels of nitrogen (N), namely 0, 75 and 100 % of the recommended dose of nitrogen (RDN), on the dry matter accumulation (DMA) and productivity of three cropping systems (sole soybean, sole sorghum and soybean + sorghum intercropping) during the rainy season and their residual effect on the subsequent wheat crop during the post-rainy season. During the rainy season, sole sorghum was found to have significantly higher DMA and productivity in terms of soybean equivalent yield (SEY) than sole soybean or soybean + sorghum intercropping. Increasing the N dose from 0 to 100 % RDN significantly improved the DMA and SEY. At a low fertility level (N0), soybean + sorghum intercropping was found to be more productive, while at a high fertility level (100 % RDN), sole sorghum was more productive than the other two cropping systems. However, during the post-rainy season, sole soybean as the preceding crop gave the highest DMA and seed yield of wheat, which were similar to those found with soybean + sorghum intercropping. Sorghum followed by wheat gave the lowest DMA and seed yield of wheat. Application of 100 % RDN irrespective of cropping system during the preceding crop improved the DMA of wheat but not its seed yield. However, N applied to the wheat crop significantly increased its DMA and seed yield. Einfluss von Stickstoff auf Trockenmasseakkumulation und Produktivität von drei Anbausystemen und deren Rückstandswirkung auf Weizen in einem tiefen Vertisol Zentralindiens Ein Feldexperiment wurde durchgeführt auf einem tiefen Vertisol bei Bhopal, Indien, um den Einfluss von drei Stickstoffkonzentrationen 0, 75 und 100 % der empfohlenen Stickstoffmenge (RDN) auf die Trockenmasseakkumulation (DMA) und Produktivität von drei Anbausystemen (Reinanbau Sojabohne, Reinanbau Sorghum und Sojabohne + Sorghum Mischanbau) während der Regensaison und deren Nachwirkungen auf den folgenden Anbau von Weizen während der Nachregensaison zu untersuchen. Während der Regensaison war der Reinanbau von Sorghum signifikant höher in DMA und in der Produktivität in Form von Ertragsäquivalenten für Sojabohnen (SEY) im Vergleich zu einem Reinanbau von Sojabohne oder einem Mischanbau von Sojabohne + Sorghum. Eine Erhöhung der N-Anwendung von 0 bis 100 % RDN erhöhte Signifikanz DMA und SEY. Unter der niedrigen Düngung (N0) erwies sich Sojabohne + Sorghum Mischanbau als produktiver im Vergleich zu einer hohen Düngungeranwendung (100 % RDN), Reinanbau war produktiver als die anderen beiden Anbausysteme. Allerdings während der Nachregensaison erwies sich der Reinanbau von Sojabohnen vor Weizen als die höchste DMA und Ertragsmenge, was mit dem Sojabohnen + Sorghum Mischanbau vergleichbar war. Sorghum gefolgt von Weizen ergab den geringsten DMA und niedrigsten Weizenertrag. Die Anwendung von 100 % RDN erhöhte unabhängig von dem Anbausystem der vorhergehenden Kulturpflanzen DMA von Weizen aber nicht den Kornertrag. Allerdings erhöhte N im Weizenanbau signifikant sowohl DMA als auch Kornertrag. [source]

    Effect of Different Crop Densities of Winter Wheat on Recovery of Nitrogen in Crop and Soil within the Growth Period

    K. Blankenau
    Previous experiments have shown that, at harvest of winter wheat, recovery of fertilizer N applied in early spring [tillering, Zadok's growth stage (GS) 25] is lower than that of N applied later in the growth period. This can be explained by losses and immobilization of N, which might be higher between GS 25 and stem elongation (GS 31). It was hypothesized that a higher crop density (i.e. more plants per unit area) results in an increased uptake of fertilizer N applied at GS 25, so that less fertilizer N is subject to losses and immobilization. Different crop densities of winter wheat at GS 25 were established by sowing densities of 100 seeds m,2 (Slow), 375 seeds m,2 (Scfp= common farming practice) and 650 seeds m,2 (Shigh) in autumn. The effect of sowing density on crop N uptake and apparent fertilizer N recovery (aFNrec = N in fertilized treatments , N in unfertilized treatments) in crops and soil mineral N (Nmin), as well as on lost and immobilized N (i.e. non-recovered N = N rate , aFNrec), was investigated for two periods after N application at GS 25 [i.e. from GS 25 to 15 days later (GS 25 + 15d), and from GS 25 + 15d to GS 31] and in a third period between GS 31 and harvest (i.e. after second and third N applications). Fertilizer N rates varied at GS 25 (0, 43 and 103 kg N ha,1), GS 31 (0 and 30 kg N ha,1) and ear emergence (0, 30 and 60 kg ha,1). At GS 25 + 15d, non-recovered N was highest (up to 33 kg N ha,1 and up to 74 kg N ha,1 at N rates of 43 and 103 kg N ha,1, respectively) due to low crop N uptake after the first N dressing. Non-recovered N was not affected by sowing density. Re-mineralization during later growth stages indicated that non-recovered N had been immobilized. N uptake rates from the second and third N applications were lowest for Slow, so non-recovered N at harvest was highest for Slow. Although non-recovered N was similar for Scfp and Shigh, the highest grain yields were found at Scfp and N dressings of 43 + 30 + 60 kg N ha,1. This combination of sowing density and N rates was the closest to common farming practice. Grain yields were lower for Shigh than for Scfp, presumably due to high competition between plants for nutrients and water. In conclusion, reducing or increasing sowing density compared to Scfp did not reduce immobilization (and losses) of fertilizer N and did not result in increased fertilizer N use efficiency or grain yields. Einfluß unterschiedlicher pflanzendichten von Winterweizen auf die Wiederfindung von Stickstoff in Pflanze und Boden während der Vegetationsperiode Aus Wintergetreideversuchen ist bekannt, daß zur Ernte die Wiederfindung von Düngerstickstoff aus der Andüngung (Bestockung, [GS-Skala nach Zadok] GS 25) im Aufwuchs und in mineralischer Form im Boden (Nmin) niedriger ist als die von Düngerstickstoff der Schosser-und Ährengaben. Dies kann auf höhere Verluste bzw. eine höhere Immobilisation von Düngerstickstoff zwischen GS 25 und Schoßbeginn zurückgeführt werden, da hier die N-Aufnahme der Pflanzen im Vergleich zu späteren Wachstumsstadien gering ist. Daraus wurde abgeleitet, daß eine Erhöhung der Pflanzendichte zu einer erhöhten Aufnahme von früh gedüngtem N führen könnte, so daß weniger Dünger-N für Verlust- und Immobilisationsprozesse im Boden verbleibt. Unterschiedliche Pflanzendichten wurden durch unterschiedliche Aussaatstärken im Herbst erreicht (Slow= 100 Körner m,2, Scfp [herkömmliche Praxis]= 375 Körner m,2, Shigh= 650 Körner m,2). In der folgenden Vegetationsperiode wurde der Einfluß der verschiedenen Aussaatstärken auf die N-Aufnahme, die apparente Wiederfindung von Dünger-N (aFNrec = N in gedüngten , N in ungedüngten Prüfgliedern) in Pflanzen und Nmin, sowie auf potentielle Verluste und Immobilisation von Dünger-N (N-Defizit = N-Düngung , aFNrec) für zwei Phasen im Zeitraum zwischen der ersten N-Gabe (GS 25) und der Schossergabe zu GS 31 (d. h. zwischen GS 25 und 15 Tagen später [GS 25 + 15d] und von GS 25 + 15d bis GS 31), sowie zwischen GS 31 und der Ernte (d. h. nach der zweiten und dritten N-Gabe) untersucht. Die N-Düngung variierte zu den Terminen GS 25 (0, 43, 103 kg N ha,1), GS 31 (0, 30 kg N ha,1) und zum Ährenschieben (0, 30, 60 kg N ha,1). Unabhängig von der Aussaatstärke war das N-Defizit zum Termin GS 25 + 15d am höchsten (bis zu 33 kg N ha,1 und 74 kg N ha,1 bei einer N-Düngung von 43 bzw. 103 kg N ha,1), da die N-Aufnahme durch die Pflanzen während der Bestockungsphase am geringsten war. Das N-Defizit zeigt vornehmlich immobilisierten N an, da zu späteren Terminen eine Re-Mobilisation von N auftrat. Zwischen GS 31 und der Ernte wurden für die Aussaatstärke Slow die geringsten Aufnahmeraten von Düngerstickstoff aus der Schosser- und Ährengabe errechnet, so daß für Slow die höchsten N-Defizitmengen ermittelt wurden. Obwohl die N-Defizitmengen für Scfp und Shigh annähernd gleich waren, wurden bei N-Düngung von 43 + 30 + 60 kg N ha,1 für Scfp die höchsten Kornerträge erzielt. Diese Kombination von Aussaatstärke und N-Düngung kann als praxisüblich bezeichnet werden. Für Shigh wurden vermutlich niedrigere Kornerträge erzielt, weil die Konkurrenz um Nährstoffe und Wasser zwischen den Pflanzen aufgrund der hohen Pflanzendichte am intensivsten war. Die Ergebnisse lassen den Schluß zu, daß eine Verringerung oder Erhöhung der Pflanzendichte über entsprechende Aussaatstärken nicht zu einer Reduktion der Dünger-N-Immobilisation (oder von N-Verlusten) führt und demnach auch nicht die Dünger-N-Ausnutzung durch die Bestände erhöht wird. [source]