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PubMed1989

Response of Ulmus americana seedlings to varying nitrogen and water status. 2 Water and nitrogen use efficiency in photosynthesis.

Photosynthetic utilization of water and nitrogen in Ulmus americana L. seedlings was tightly linked with the relative availability of each resource. During periodic drying cycles, water use efficiency increased as predawn water potential fell from -0.5 to -2.0 MPa. During the later stages of such drying cycles, the relative contribution of stomatal limitations to the total net photosynthetic limitation appeared to be at its greatest, whereas biochemical limitations were predominant in well-watered plants grown under low nitrogen (N) availability. For any level of leaf water status, water use efficiency of photosynthesis (WUE) was always greater in plants with high leaf N content than in plants with low leaf N content. Photosynthetic nitrogen use efficiency (PNUE) was always greater in plants with low leaf N content than in plants with high leaf N content, for any level of water status. In combined N treatments and predawn water status classes, there was a significant inverse relationship between PNUE and WUE.

Journal Article↗
PubMed2006

Direct observation of nitrogen location in molecular beam epitaxy grown nitrogen-doped ZnO.

ZnO is a wide band gap, naturally n-type semiconductor with great promise for optoelectronic applications; the main obstacle yet to be overcome is p-type doping. Nitrogen, the most promising candidate currently being pursued as a dopant, has been predicted to preferentially incorporate into the ZnO lattice in the form of a N-2 molecule at an O site when a plasma source is used, leading to compensation rather than p-type doping. We demonstrate this to be incorrect by using N K-edge x-ray absorption spectra and comparing them with first-principles calculations showing that nitrogen, in fact, incorporates substitutionally at O sites where it is expected to act as an acceptor. We also detect the formation of molecular nitrogen upon annealing. These results suggest that effective p-type doping of ZnO with N may be possible only for low-temperature growth processes.

Journal Article↗
PubMed1980

Increase in Dry Weight and Total Nitrogen Content in Zea mays and Setaria italica Associated with Nitrogen-fixing Azospirillum spp.

The association between nitrogen-fixing bacteria from the genus Azospirillum and the grasses Zea mays and Setaria italica was investigated in sterilized Leonard-jar assemblies. Nitrogen-fixing bacteria isolated from Cynodon dactylon roots in Israel and Azospirillum brasilense (Sp-7, Sp-80, and Cd) were examined. C(2)H(2) reduction activity was detected in systems containing 0.0 to 0.08 but not in those containing 0.16 gram per liter NH(4)NO(3). The organisms tested significantly increased plant dry weight (50-100%), total N content of leaves (50-100%) and C(2)H(4) production (300-1000 nanomoles C(2)H(4) per plant per hour). Highest C(2)H(2) reduction activities were obtained above 30 C and with high light intensities. Significant increases in S. italica dry weight (DW) and nitrogen (N) content were observed in sand (DW = 80%, N = 150%), sandy loam soil (DW = 80%, N = 75%) and loess (DW = 37%, N = 25%). The results obtained in this work clearly demonstrate the potential benefit of inoculating grasses with Azospirillum.

Journal Article↗
PubMed1979

Nitrogen-fixing (acetylene redution) activity and population of aerobic heterotrophic nitrogen-fixing bacteria associated with wetland rice.

Nitrogen-fixing activity associated with different wetland rice varieties was measured at various growth stages by an in situ acetylene reduction method after the activities of blue-green algae (cyanobacteria) in the flood water and on the lower portion of the rice stem were eliminated. Nitrogen-fixing activities associated with rice varieties differed with plant growth stages. The activities increased with plant age, and the maximum was about at heading stage. The nitrogen fixed during the whole cropping period was estimated at 5.9 kg of N per ha for variety IR26 (7 days) and 4.8 kg of N per ha for variety IR36 (95 days). The population of aerobic heterotrophic N(2)-fixing bacteria associated with rice roots and stems was determined by the most-probable-number method, using semisolid glucose-yeast extract and semisolid malate-yeast extract media. The addition of yeast extract to the glucose medium increased the number and activity of aerobic heterotrophic N(2)-fixing bacteria. The glucose-yeast extract medium gave higher counts of aerobic N(2)-fixing bacteria associated with rice roots than did the malate-yeast extract medium, on which Spirillum-like bacteria were usually observed. The lower portion of the rice stem was also inhabited by N(2)-fixing bacteria and was an active site of N(2) fixation.

Journal Article↗
PubMed1993

Identification of the sources of energy for nitrogen fixation and physiological characterization of nitrogen-fixing members of a marine microbial mat community.

Experimental manipulations of a microbial mat community were performed to determine sources of energy and reductant used for nitrogen fixation and to physiologically characterize the responsible diazotrophs. The dominant photolithotrophic members of this community were nonheterocystous cyanobacteria, but other potential nitrogen-fixing microorganisms were also present. Pronounced diel variability in rates of acetylene reduction was observed, with nighttime rates a factor of three to four higher than daytime rates. Acetylene reduction measured at night was dependent upon the occurrence of oxygenic photosynthesis the preceding day; mats incubated in the dark during the daytime reduced acetylene at rates comparable to those of light-incubated mats but were not able to reduce acetylene at the normally high rates the following night. The addition of various exogenous carbon compounds to these dark-incubated mats did not elicit nighttime acetylene reduction. Nighttime acetylene reduction apparently proceeds under anoxic conditions in these mats; the highest rates of acetylene reduction occur late at night. Additions of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (an inhibitor of oxygenic photosynthesis) to mats resulted in a pronounced stimulation of acetylene reduction during the day, but acetylene reduction the next night proceeded at greatly reduced rates (relative to untreated mats). This daytime stimulation, under the 3-(3,4-dichlorophenyl)-1,1-dimethylurea-induced anoxic conditions in the experimentally treated mats, was light dependent. These results suggest that nitrogen fixation in these mats may be attributed to the activities of nonheterocystous cyanobacteria utilizing storage products of oxygenic photosynthesis under anoxic conditions at night.

Journal Article↗
PubMedDate not supplied

[The effect of the plant growth stimulant bactozole on Rhizobium leguminosarum bv. viciae 250a and its nitrogen-tolerant mutant M-71 under varied nitrogen supply].

The effect of the plant growth stimulant bactozole on the growth of Rhizobium leguminosarum bv. viciae 250a and its nitrogen-tolerant mutant M-71 and the synthesis of extracellular carbohydrates was studied. At a low content of nitrate (6 mM) in the medium, all three bactozole concentrations tested (0.001, 0.01, and 0.1%) exerted similar stimulating effects on the growth of the parent strain 250a (about 1.5-fold) and the synthesis of extracellular carbohydrates (about 2-fold). At a high content of nitrate (20 mM) in the medium, when the growth of the parent strain and the synthesis of extracellular carbohydrates were inhibited, bactozole at all three concentrations exerted only a growth-stimulating effect. At the same time, mutant M-71 showed better growth at higher concentrations of bactozole, whereas the ability of the mutant to synthesize extracellular carbohydrates decreased with increasing bactozole concentration. The cell biomass of the mutant accumulated at 20 mM nitrate was 1.8-2.5 times greater than it was at 6 mM nitrate. Bactozole enhanced the symbiosis of legume plants with both parent and mutant strains, raising the mass of plants and enhancing nodulation and the nitrogen-fixing activity of root nodules. The symbiotic parameters of mutant M-71 were better (irrespective of whether bactozole was present or not) when its inoculum was grown at a high nitrogen content (20 mM nitrate), whereas the respective parameters of the parent strain were better when it was grown at 6 mM nitrate. The inference is made that the better physiological characteristics of the mutant in the high-nitrate medium is due to its higher nitrate reductase activity (as compared with the parent strain) in both the free-living state and in legume nodules.

Carbohydrates↗
PubMed2005

Dynamics of exogenous nitrogen partitioning and nitrogen remobilization from vegetative organs in pea revealed by 15N in vivo labeling throughout seed filling.

The fluxes of (1) exogenous nitrogen (N) assimilation and (2) remobilization of endogenous N from vegetative plant compartments were measured by 15N labeling during the seed-filling period in pea (Pisum sativum L. cv Cameor), to better understand the mechanism of N remobilization. While the majority (86%) of exogenous N was allocated to the vegetative organs before the beginning of seed filling, this fraction decreased to 45% at the onset of seed filling, the remainder being directed to seeds. Nitrogen remobilization from vegetative parts contributed to 71% of the total N in mature seeds borne on the first two nodes (first stratum). The contribution of remobilized N to total seed N varied, with the highest proportion at the beginning of filling; it was independent of the developmental stage of each stratum of seeds, suggesting that remobilized N forms a unique pool, managed at the whole-plant level and supplied to all filling seeds whatever their position on the plant. Once seed filling starts, N is remobilized from all vegetative organs: 30% of the total N accumulated in seeds was remobilized from leaves, 20% from pod walls, 11% from roots, and 10% from stems. The rate of N remobilization was maximal when seeds of all the different strata were filling, consistent with regulation according to the N demand of seeds. At later stages of seed filling, the rate of remobilization decreases and may become controlled by the amount of residual N in vegetative tissues.

Kinetics↗
PubMed1989

The Azorhizobium caulinodans nitrogen-fixation regulatory gene, nifA, is controlled by the cellular nitrogen and oxygen status.

The nucleotide sequence of the Azorhizobium caulinodans ORS571 nifA locus was determined and the deduced NifA amino acid sequence compared with that of NifA from other nitrogen-fixing species. Highly conserved domains, including helix-turn-helix and ATP-binding motifs, and specific conserved residues, such as a cluster of cysteines, were identified. The nifA 5' upstream region was found to contain DNA sequence motifs highly homologous to promoter elements involved in nifA/ntr-mediated control and a consensus element found in the 5' upstream region of the Bradyrhizobium japonicum 5-aminolevulinic acid synthase (hemA) gene and of Escherichia coli genes activated during anaerobiosis via the fnr (fumarate nitrate reduction) control system. A nifA-lac fusion was constructed using miniMu-lac and its activity measured in different genetic backgrounds and under various physiological conditions (in culture and in planta). NifA expression was found to be negatively autoregulated, repressed by rich nitrogen sources and high oxygen concentrations, and controlled (partially) by the ntrC gene, both in culture and in planta. DNA supercoiling was also implicated in nifA regulation, since DNA gyrase inhibitors severely repressed nifA-lac expression.

Amino Acid Sequence↗
PubMed1997

Regulation of nitrogen fixation by different nitrogen sources in the filamentous non-heterocystous cyanobacterium Microcoleus sp.

The pattern of N2 fixation, the synthesis and activity of nitrogenase under different nitrogen sources was studied in the filamentous, non-heterocystous cyanobacterium Microcoleus sp. grown under defined culture conditions. Cells grown under a 10 h light/14 h dark (10L/14D) cycle with N2 as an inorganic nitrogen source showed highest nitrogenase activity (acetylene reduction) at the end of the light phase and then a decrease after entering the dark phase. Nitrogenase synthesis was neither suppressed after 7 days of growth with 2 mM NaNO3 or 0.2 mM (NH4)2SO4 or 0.3 mM urea nor with 20 mM NaNO3 or 3 mM (NH4)2SO4 or 4 mM urea under the 10L/14D cycle. Western immunoblots tested with polyclonal antisera against the Fe-protein revealed the following: (1) the Fe-protein was synthesized in cells grown with N2 as well as in cells grown with NaNO3 or (NH4)2SO4 under the 10L/14D cycle; (2) the Fe-protein was found in cells grown with urea under the 10L/14D cycle, but not in the darkness; (3) only one protein band, corresponding to the Fe-protein, was found in cells harvested during the light phase of the 10L/14D cycle under the tested conditions. No nitrogenase activity was observed when chloramphenicol was added to the cultures 4 h before the onset of the light period. This observation suggest de novo synthesis of nitrogenase in Microcoleus sp.

Acetylene↗
PubMed2003

Measurement and modeling of ozone and nitrogen oxides produced by laser breakdown in oxygen-nitrogen atmospheres.

The production of ozone nad nitrogen oxides was studied during multiple laser breakdown in oxygen-nitrogen mixtures at atmospheric pressure. About 2000 laser shots at 10(10) W cm-2 were delivered into a sealed reaction chamber. The chamber with a long capillary was designed to measure absorption of O3, NO, and NO2 as a function of the number of laser shots. The light source for absorption measurements was the continuum radiation emitted by the plasma during the first 0.2 microsecond of its evolution. A kinetic model was developed that encompassed the principal chemical reactions between the major atmospheric components and the products of laser breakdown. In the model, the laser plasma was treated as a source of nitric oxide and atomic oxygen, whose rates of production were calculated using measured absorption by NO, NO2, and O3. The calculated concentration profiles for NO, NO2, and O3 were in good agreement with measured profiles over a time scale of 0-200 s. The steady-state concentration of ozone was measured in a flow cell in air. For a single breakdown in air, the estimated steady-state yield of ozone was 2 x 10(12) molecules, which agreed with the model prediction. This study can be of importance for general understanding of laser plasma chemistry and for elucidating the nature of spectral interferences and matrix effects that may take place in applied spectrochemical analysis.

Flow Injection Analysis↗
PubMed2006

Effects of phase-feeding of crude protein on performance, carcass characteristics, serum urea nitrogen concentrations, and manure nitrogen of finishing beef steers.

As cattle mature, the dietary protein requirement, as a percentage of the diet, decreases. Thus, decreasing the dietary CP concentration during the latter part of the finishing period might decrease feed costs and N losses to the environment. Three hundred eighteen medium-framed crossbred steers (315 +/- 5 kg) fed 90% (DM basis) concentrate, steam-flaked, corn-based diets were used to evaluate the effect of phase-feeding of CP on performance and carcass characteristics, serum urea N concentrations, and manure characteristics. Steers were blocked by BW and assigned randomly to 36 feedlot pens (8 to 10 steers per pen). After a 21-d step-up period, the following dietary treatments (DM basis) were assigned randomly to pens within a weight block: 1) 11.5% CP diet fed throughout; 2) 13% CP diet fed throughout; 3) switched from an 11.5 to a 10% CP diet when approximately 56 d remained in the feeding period; 4) switched from a 13 to an 11.5% CP diet when 56 d remained; 5) switched from a 13 to a 10% CP diet when 56 d remained; and 6) switched from a 13 to an 11.5% CP diet when 28 d remained. Blocks of cattle were slaughtered when approximately 60% of the cattle within the weight block were visually estimated to grade USDA Choice (average days on feed = 182). Nitrogen volatilization losses were estimated by the change in the N:P ratio of the diet and pen surface manure. Cattle switched from 13 to 10% CP diets with 56 d remaining on feed or from 13 to 11.5% CP with only 28 d remaining on feed had lower (P < 0.05) ADG, DMI, and G:F than steers fed a 13% CP diet throughout. Steers on the phase-feeding regimens had lower (P = 0.05) ADG and DMI during the last 56 d on feed than steers fed 13.0% CP diet throughout. Carcass characteristics were not affected by dietary regimen. Performance by cattle fed a constant 11.5% CP diet did not differ from those fed a 13% CP diet. Serum urea N concentrations increased (P < 0.05) with increasing dietary CP concentrations. Phase-feeding decreased estimated N excretion by 1.5 to 3.8 kg/steer and nitrogen volatilization losses by 3 to 5 kg/steer. The results suggest that modest changes in dietary CP concentration in the latter portion of the feeding period may have relatively small effects on overall beef cattle performance, but that decreasing dietary CP to 10% of DM would adversely affect performance of cattle fed high-concentrate, steam-flaked, corn-based diets.

Animal Feed↗
PubMed2001

The relationship of milk urea nitrogen to urine nitrogen excretion in Holstein and Jersey cows.

The objectives of this study were to assess the relationship between urinary nitrogen excretion (UN, g/d) and milk urea nitrogen concentration (MUN, mg/dl) and whether the types of carbohydrates fed interacts with the dietary CP and the breed (size) of cows to affect this relationship. Eight multiparous cows (four Holstein and four Jersey) were fed four different diets in a 2 x 2 factorial arrangement of levels of crude protein (13 and 17%) and levels of neutral detergent fiber (30 and 40%). The experimental design was a split plot Latin square with breeds forming the main plots and diets forming the subplots. Experimental periods were 3 wk in length, with d 1 to 14 used for adjustment and d 15 to 19 used for a total collection of urine and feces. Crude protein concentrations had a significant effect on milk, milk fat and protein production, plasma urea N, MUN, and on N balance measurements (N intake, fecal and urinary N excretion, milk N production, N retention, apparent N digestibility, and N efficiency). Neutral detergent fiber levels had no effect on any production parameters or N balance measurements. The relationship between urinary N and MUN was linear over the range of MUN values observed and different for the two breeds. The breed effect on the UN-MUN relationship was no longer significant (P = 0.63) when body weight (BW) was included in the model. The optimal allometric coefficient for BW was 0.96 and was not different from 1.0. Therefore, the following equation is proposed to predict UN excretion based on MUN and BW: UN (g/d) = 0.0259 (+/- 0.0006) BW (kg) x MUN (mg/dl).

Animals↗
PubMed2002

Use of nitrogen stable isotope ratio of periphyton for monitoring nitrogen sources in a river system.

In order to confirm the usefulness of the N stable isotope ratio of periphyton (mainly composed of attached algae) as an indicator for monitoring the N sources in river watersheds, we measured the isotope ratio of periphyton along the Chikuma River. In the river, both the concentrations of dissolved total nitrogen (DTN) and the delta15N values of periphyton increased downstream. Specific nitrogen loading rates (SNLR) calculated from administrative data also showed an increase downstream from 7 to 11 kg N ha(-1) yr(-1), with the increasing contribution by sewage and livestock waste from 6 to 40% to total N loading. There are significant positive relationships between the DTN concentration and the SNLR (r2=0.54, P<0.05), and the delta15N values of periphyton and the SNLR (r2=0.78, P<0.05). The increase in DTN concentration reflected the increase in input of N loading. The increase in delta15N of periphyton might reflect the increase in relative contribution by sewage and livestock waste down the river, especially the increase in sewage. The present study indicates the usefulness of the N stable isotope ratio of periphyton as an indicator for monitoring N sources in a river system.

Animals↗
PubMed2005

Tracing the influence of sewage nitrogen in a coastal ecosystem using stable nitrogen isotopes.

This paper reviews the use of stable nitrogen isotopes (delta15N) to delineate the influence of sewage nitrogen (N) in coastal ecosystems, drawing extensively on the case of Himmerfjärden, a Baltic Sea bay that receives 15N-enriched tertiary treated sewage that is discharged mainly as dissolved inorganic N (DIN). Gradients of delta15N in macroalgae (Fucus vesiculosus) and surface sediments traced sewage-derived N to 24 km from the outfall but elevated delta15N values (> 7 per thousand) indicated that the sewage influence was most pronounced within 10 km. Comparison of macroalgal delta15N values before and after enhanced tertiary treatment showed a decrease in the spatial impact of sewage N from about 24 km to 12 km from the outfall and a decrease to more marine delta15N values in more recent growth tissues. Sedimentary delta15N records showed that sewage has had a dominant influence on organic matter production in the bay with dramatic increases in sedimentary delta15N during the years of maximum sewage N loads. In cases where sewage N introduces a distinct isotopic signature into a system and where it has had a dominant influence on organic matter production, delta15N values in biota and sediments can be used to trace the spatial and temporal influence of sewage N in aquatic ecosystems.

Ecosystem↗
PubMed1994

Effect of mutations in Escherichia coli glnL (ntrB), encoding nitrogen regulator II (NRII or NtrB), on the phosphatase activity involved in bacterial nitrogen regulation.

We examined the effects of mutations in glnL, encoding the signal-transducing kinase/phosphatase nitrogen regulator II (NRII), on the regulated phosphatase activity involved in nitrogen regulation. With wild-type NRII, this phosphatase activity was only observed in the presence of the signal transduction protein II (PII). Three different glnL mutations result in altered NRII proteins that had phosphatase activity in the absence of PII. The most active of these contained an alteration of the site of NRII autophosphorylation, histidine 139, to asparagine (H139N). The phosphatase activity of the NRII-H139N protein was further stimulated by the PII protein and by ATP. This suggests that the PII protein is not directly involved in a catalytic step of the regulated phosphatase activity but rather plays a regulatory role. We also measured the effect on the regulated phosphatase activity of alterations at conserved residues in the kinase/phosphatase domain of NRII and the effect of deleting the non-conserved N-terminal domain of NRII. For this we used fusion proteins containing the Escherichia coli maltose-binding protein (MBP) linked to the protein of interest. A protein consisting of MBP linked to wild-type NRII was a less active kinase than was wild-type NRII but in the presence of PII had wild-type phosphatase activity. A protein consisting of MBP linked to just the C-terminal domain of wild-type NRII had kinase activity but lacked phosphatase activity. Alterations at the highly conserved residues Asp-287, Gly-289, and Gly-291 in NRII affected both activities. A fusion of MBP to the NRII-H139N protein lacked kinase activity but had phosphatase activity in the absence of PII. Thus, while the kinase and phosphatase activities of NRII could be genetically separated, some of the highly conserved residues in the C-terminal domain of NRII (Asp-287, Gly-289, Gly-291) are apparently important for both activities.

Amino Acid Sequence↗
PubMed2005

Pulse additions of soil carbon and nitrogen affect soil nitrogen dynamics in an arid Colorado Plateau shrubland.

Biogeochemical cycles in arid and semi-arid ecosystems depend upon the ability of soil microbes to use pulses of resources. Brief periods of high activity generally occur after precipitation events that provide access to energy and nutrients (carbon and nitrogen) for soil organisms. To better understand pulse-driven dynamics of microbial soil nitrogen (N) cycling in an arid Colorado Plateau ecosystem, we simulated a pulsed addition of labile carbon (C) and N in the field under the canopies of the major plant species in plant interspaces. Soil microbial activity and N cycling responded positively to added C while NH (4) (+) -N additions resulted in an accumulation of soil NO (3) (-) . Increases in microbial activity were reflected in higher rates of respiration and N immobilization with C addition. When both C and N were added to soils, N losses via NH(3) volatilization decreased. There was no effect of soil C or N availability on microbial biomass N suggesting that the level of microbial activity (respiration) may be more important than population size (biomass) in controlling short-term dynamics of inorganic and labile organic N. The effects of C and N pulses on soil microbial function and pools of NH (4) (+) -N and labile organic N were observed to last only for the duration of the moisture pulse created by treatment addition, while the effect on the NO (3) (-) -N pool persisted after soils dried to pre-pulse moisture levels. We observed that increases in available C lead to greater ecosystem immobilization and retention of N in soil microbial biomass and also lowered rates of gaseous N loss. With the exception of trace gas N losses, the lack of interaction between available C and N on controlling N dynamics, and the subsequent reduction in plant available N with C addition has implications for the competitive relationships between plants species, plants and microbes, or both.

Bacterial Physiological Phenomena↗
PubMed2006

Stoichiometric response of nitrogen-fixing and non-fixing dicots to manipulations of CO2, nitrogen, and diversity.

Human activities have resulted in increased nitrogen deposition and atmospheric CO(2) concentrations in the biosphere, potentially causing significant changes in many ecological processes. In addition to these ongoing perturbations of the abiotic environment, human-induced losses of biodiversity are also of major concern and may interact in important ways with biogeochemical perturbations to affect ecosystem structure and function. We have evaluated the effects of these perturbations on plant biomass stoichiometric composition (C:N:P ratios) within the framework of the BioCON experimental setup (biodiversity, CO(2), N) conducted at the Cedar Creek Natural History Area, Minnesota. Here we present data for five plant species: Solidago rigida, Achillea millefolium, Amorpha canescens, Lespedeza capitata, and Lupinus perennis. We found significantly higher C:N and C:P ratios under elevated CO(2) treatments, but species responded idiosyncratically to the treatment. Nitrogen addition decreased C:N ratios, but this response was greater in the ambient CO(2) treatments than under elevated CO(2). Higher plant species diversity generally lowered both C:N and C:P ratios. Importantly, increased diversity also led to a more modest increase in the C:N ratio with elevated CO(2) levels. In addition, legumes exhibited lower C:N and higher C:P and N:P ratios than non-legumes, highlighting the effect of physiological characteristics defining plant functional types. These data suggest that atmospheric CO(2) levels, N availability, and plant species diversity interact to affect both aboveground and belowground processes by altering plant elemental composition.

Asteraceae↗
PubMed2005

Modeling nitrogen uptake and potential nitrate leaching under different irrigation programs in nitrogen-fertilized tomato using the computer program NLEAP.

Readily available nitrogen (N) sources such as ammonium nitrate with excessive irrigation present a potential hazard for the environment. The computer program Nitrate Leaching and Economic Analysis Package (NLEAP) is a mechanistic model developed for rapid site-specific estimates of nitrate-nitrogen (NO3-N) moving below the root zone in agricultural crops and potential impacts of NO3-N leaching into groundwater. In this study, the value of NLEAP was tested to simulate N uptake by crops and NO3-N leaching parameters in large lysimeters under the tomato crop. Three seedlings of tomato variety of H-2274 (Lycopersicum esculentum L.) were transplanted into each lysimeter. N fertilizer at the rate of 140 kg N ha(-1) was sidedressed in two split applications, the first half as ammonium sulphate and the second half as ammonium nitrate. The lysimeters were irrigated based on programs of C 0.75, 1.00, 1.25 and 1.50, C referring to class A-Pan evaporation coefficients. Parameters such as leaching index (LI), annual leaching risk potential (ALRP), N available for leaching (NAL), amount of NO3-N leached (NL) and amount of N taken up by the crops (NU) were estimated using the NLEAP computer model. To test the ability of model to simulate N uptake and NL, measured values were compared with simulated values. Significant correlations, R2 = 0.92 and P < 0.03 for the first year and R2 = 0.86 and P < 0.06 for the second year, were found between measured and simulated values for crop N consumption, indicating that the NLEAP model adequately described crop N uptake under the varied irrigation programs using an optimal N fertilization program for the experimental site. Significant correlations, R2 = 0.96 and P < 0.01 for the first year and R2 = 0.97 and P < 0.01 for the second year, were also found between measured and simulated values of NL, indicating that the NLEAP model also adequately predicted NL under the varied irrigation programs. Therefore, this computer model can be useful to estimate the NO3-N moving beyond the root zone under conditions in which the present experiment was carried out. Also, the NLEAP-estimated NAL values and other parameters can also be used to improve N management practices and N fertilizer recommendations that will help to decrease the adverse effect of N fertilizer on groundwater quality and farm profitability.

Agriculture↗