Low Levels Of NO3 Research Articles

Salt stress effects on enzymes activities involved in carbon metabolism and nitrogen availability of two Tunisian durum wheat varieties

Two varieties of durum wheat (Om Rabiaa and Karim), were analyzed and evaluated in the presence of increasing doses of NaCl (0, 100, 200 and 300 mM) in which we added different concentrations of nitrate (0.1, 3, 10 mM). The data obtained showed that presence of NaCl in the culture medium induces the increase of the salt accumulation levels (Na+, Cl−) and reduces the levels of K+ and NO3− in the cultivar Om Rabiaa. In Karim variety, ions that have been heavily accumulated following exposure to NaCl are Na+ and K+ while low levels of NO3− and Cl− have been detected. Those findings highlight the difference in the salinity tolerance of durum wheat cultivars also depending on nitrogen (N) availability, Karim cultivar being less sensitive to NaCl treatment than Om Rabiaa. These data also suggested a relationship between salt tolerance capacity and enhancement of nitrogen and carbon metabolisms enzyme activity.

Distribution of arsenic in core sediments and groundwater in the Chapai Nawabganj district, Bangladesh

Arsenic (As) concentration and geochemical analysis of groundwater as well as core sediments of 20 tube wells revealed the uppermost aquifer (20–40 m of depth) groundwater As concentrations ranging from 2.34 to 586.96 μg L−1, and groundwater geochemical conditions change from oxidized to gradually more reduced as higher concentrations of As increased with depth. The highest sediment As levels (25 mg kg−1) were found within the shallow depth (15 m). The groundwater of the study area is of Ca-HCO3 type, where Ca is the dominant metal with high concentrations of As, Fe, and Mn but low levels of NO3− and SO42−. The trace elements Fe, Mn, and As exceed the WHO and DoE standard in groundwater which clearly indicated As contamination except some few areas where less Fe and Mn are released in aquifer water from sediment. The contaminated As zone also corroborated with the GIS study. Considerable variability with depth and location is noted in the levels of As, Fe, and Mn in groundwater, and from these levels it can be seen that the groundwater of Rajarampur village of Chapai Nawabganj Paurasava is more reduced than the groundwater of Baragharia. Groundwater in Baragharia village contains low concentration of As below the WHO standard (< 10 μg L−1), and this type of water is generally suitable for extraction for domestic uses. Some places have been detected as having the most favorable conditions for reducing the environment where higher concentrations of As are observed. Fine-grained sediments are also associated with high levels of As concentration in aquifers. Statistical analysis clearly shows that As is closely related with Fe (R2 = 0.557) and Mn (R2 = 0.627) in sediments. However, As is not well correlated with Mn (R2 = 0.2175) in groundwater. These correlations indicate that the reductive destruction of Mn- and Fe-rich compounds (e.g., MnOOH, FeOOH) is controlled by anaerobic bacteria states for releasing As into the aquifer. Notwithstanding, in spite of the poor correlation between As and Fe, As and Mn bare that Fe and Mn are assumed to be precipitated onto the sediments as siderite and rhodochrosite.

Shifts in stream hydrochemistry in responses to typhoon and non-typhoon precipitation

Abstract. Climate change is projected to increase the intensity and frequency of extreme climatic events such as tropical cyclones. However, few studies have examined the responses of hydrochemical processes to climate extremes. To fill this knowledge gap, we compared the relationship between stream discharge and ion input–output budget during typhoon and non-typhoon periods in four subtropical mountain watersheds with different levels of agricultural land cover in northern Taiwan. The results indicated that the high predictability of ion input–output budgets using stream discharge during the non-typhoon period largely disappeared during the typhoon periods. For ions such as Na+, NH4+, and PO43-, the typhoon period and non-typhoon period exhibited opposite discharge–budget relationships. In other cases, the discharge–budget relationship was driven by the typhoon period, which consisted of only 7 % of the total time period. The striking differences in the discharge–ion budget relationship between the two periods likely resulted from differences in the relative contributions of surface runoff, subsurface runoff and groundwater, which had different chemical compositions, to stream discharge between the two periods. Watersheds with a 17–22 % tea plantation cover showed large increases in NO3- export with increases in stream discharge. In contrast, watersheds with 93–99 % forest cover showed very mild or no increases in NO3- export with increases in discharge and very low levels of NO3- export even during typhoon storms. The results suggest that even mild disruption of the natural vegetation could largely alter hydrochemical processes. Our study clearly illustrates significant shifts in hydrochemical responses between regular and typhoon precipitation. We propose that hydrological models should separate hydrochemical processes into regular and extreme conditions to better capture the whole spectrum of hydrochemical responses to a variety of climate conditions.

The Role of Nitrogen Availability for the Salt-Tolerance of Two Different Varieties of Durum Wheat

Salt stress tolerance of durum wheat was assessed in control and 200 and 300mM NaCl-exposed seed of two cultivars (BidiAP4 and Azizi). These salt treatments were accompanied by different levels of nitrate (Ca(NO3)2) added to the media (0.1, 3, 10mM). The data showed that NaCl stress increased Na(+) and Cl(-) contents and lowered K(+) and NO3 (-) levels in seeds of BidiAP4 cultivar. In Azizi seeds exposed to NaCl, Na(+) and K(+) were highly accumulated while low levels of NO3 (-) and Cl(-) were detected. Those findings highlight the difference in the salt stress tolerance of these two durum wheat cultivars also depending on nitrogen (N) availability, Azizi cultivar being less sensitive to NaCl treatment than BidiAP4. These data also suggested a relationship between salt tolerance capacity and enhancement or maintenance of nitrogen and carbon metabolisms enzyme activity.

The effects of NaCl stress on Jatropha cotyledon growth and nitrogen metabolism

The effects of treatment with 50 and 100 mM NaCl on cotyledon growth, nitrogen assimilation, and the activities of key nitrogen metabolism enzymes were investigated in developing Jatropha curcas cotyledons. Growth inhibition was observed, and relative water content in the developing cotyledons significantly decreased in the 100 mM NaCl treatment. Lower levels of NO3-, NO2-, and NH4+ in the cotyledons were recorded when they were supplied with 50 and 100 mM NaCl. Nitrate reductase activities decline by 9.5% to 31.8% with respect to the control groups. Salt treatment also led to a marked decrease in nitrite reductase activity compared with the controls. Glutamine synthase, glutamate synthetase and dehydrogenase, alanine aminotransferase (AlaAT) and aspartate aminotransferase (AspAT) were markedly induced by the addition of NaCl. These findings will be useful for elucidating the roles key enzymes involved in nitrogen assimilation pathway of J. curcas plant.

Rosemary extract and celery-based products used as natural quality enhancers for colonial type salami with different ripening times

This study aimed to evaluate the use of rosemary (Rosmarinus officinalis) extract (RE), celery (Apium graveolis), and low levels of NO3 and NO2 as natural agents to enhance the quality of colonial salami. Salami was produced according to three treatments: (A) Control: 0.1% curing salt; (B) Rosemary: 0.05% curing salt + 0.5% RE (rosemary extract); and (C) Rosemary+celery: 0.14% Veg 503 + 0.27% Veg 504 (sea salt plus celery) + 0.5% of RE (rosemary extract). There was no effect (P &gt; 0.05) of the treatments on water activity, Na content, and residual NO3 and NO2. Fatty acids C18:2 and C20:4 were reduced (P &lt; 0.05) during the ripening period in the Control treatment indicating possible oxidation. The use of celery resulted in lower pH values (P &lt; 0.05) in the salami. Reduced addition of NO3 and NO2 resulted in salami lighter in color (higher L* values, P &lt; 0.05) at the 12th day of ripening. In conclusion, celery-based products proved to be an effective source of NO2 and NO3 for color development, but the low pH of the product indicates the need for better evaluation of its use in fermented salami. The RE (rosemary extract) reduced fat oxidation in salami, but this needs further evaluation.

Vertical Distribution and Mobilization of Arsenic in Shallow Alluvial Aquifers of Chapai-Nawabganj District, Northwestern Bangladesh

Abstract Core sediments from two boreholes and groundwater from fifty four As-contaminated well waters were collected in the Chapai-Nawabganj area of northwestern Bangladesh for geochemical analysis. Groundwater arsenic concentrations in the uppermost aquifer (10 to 40 m of depth) range from 2.76-315.15 mg/l (average 48.81 mg/l). Arsenic concentration in sediments ranges from 3.26-10 mg/kg. Vertical distribution of arsenic in both groundwater and sediments shows that maximum As concentration (462 mg/l in groundwater and 10 mg/kg in sediments) occurs at a depth of 24 m. In January 2008, 2009 and 2010, maximum As concentration occurs at the same depth. Environmental scanning electron microscope (ESEM) with EDAX was used to investigate the presence of major and trace elements in the sediments. The dominant groundwater type is Ca-HCO3 with high concentrations of As and Fe, but with low levels of NO3- and SO4-2. Statistical analysis clearly shows that As is closely associated with Fe (R2 = 0.64) and Mn (R2 = 0.91) in sediments while As is not correlated with Fe and Mn in groundwater samples. Comparatively low Fe and Mn concentrations in some groundwater, suggest that probably siderite and/or rhodochrosite precipitated as secondary mineral on the surface of the sediment particles. The correlations along with results of sequential leaching experiments suggest that reductive dissolution of FeOOH and MnOOH mediated by anaerobic bacteria represents mechanism for releasing arsenic into the groundwater.

Stream Nitrate Responds Rapidly to Decreasing Nitrate Deposition

Ecosystem acidification and eutrophication resulting from increased deposition of dissolved inorganic nitrogen (DIN) are issues of increasing global concern. Consequently, costly policy decisions are being implemented to decrease nitrogen oxide (NOx) emissions. Although declining DIN deposition along with rapid declines of DIN in surface waters have been reported in parts of Europe, the same observation is just emerging in North America. Here we find a significant decline in bulk deposition NO3− during the later part of a 28-year record in southcentral Ontario, Canada. Despite high N retention and substantial inter-annual variability in the long-term record due to periods of drought, we find significant declines in annual NO3− concentrations and export at six out of 11 streams that drain upland-dominated catchments. In contrast, five streams draining primarily wetland-dominated catchments with lower levels of NO3− show no decreasing trend in NO3− concentration or export. The rapid response in stream NO3− to declining atmospheric inputs was observed at sites with historically moderate inputs of DIN (~870 mg m−2 y−1) in bulk deposition. Topographic features such as slope, and related catchment features including wetland cover, appear to influence which catchments will respond positively to declining DIN deposition. These findings force us to revise our original conceptualization of the N saturation status of these catchments.

Arbuscular mycorrhizas enhance plant interception of leached nutrients

Arbuscular mycorrhizal fungi (AMF) can increase plant growth and nutrition. However, their capacity to reduce the leaching of nutrients through the soil profile is less well understood. Here we present results of an experiment in which the effects of forming arbuscular mycorrhizas (AM) on plant growth and nutrition, nutrient depletion from soil, and nutrient leaching, were investigated in microcosms containing the grass Phalaris aquatica L. Mycorrhizal and non-mycorrhizal plants were grown in a mixture of riparian soil and sand under glasshouse conditions. The formation of AM by P. aquatica significantly increased plant growth and nutrient uptake. Lower levels of NO3-, NH4+ and plant available P in both soil and leachate were observed in columns containing mycorrhizal root systems. These differences in nutrient interception were proportionally greater than the increase in root biomass of the mycorrhizal plants, compared with their non-mycorrhizal counterparts. Taken together, these data indicate that mycorrhizal root systems have an important, but previously little considered, role to play reducing the net loss of nutrients via leaching.

Effects of different nitrogen sources on growth, chlorophyll concentration, nitrate reductase activity and carbon and nitrogen distribution in Araucaria angustifolia

The southern Brazilian highland plateau is a mosaic of two contrasting plant communities, Araucaria forests and grasslands, which differ in the relative abundances and spatial patterns of soil nitrate and ammonium. However, we still do not know the inorganic N preferences of one key species in this mosaic, Araucaria angustifolia, the dominant tree species in the Araucaria forests and an important tree species invading the adjacent grasslands. Growth responses measured in a greenhouse study demonstrated that the species prefers NH4+ over NO3- as an inorganic N source. When provided alone, NO3- induced N deficiency symptoms: increases in root: shoot ratio, root branching and leaf mass per area, thickening of the shoot apexes and decreased mass-based chlorophyll and N concentrations of the young leaves. Nitrate-based nutrition also affected the whole plant N and carbon (C) distribution: young leaves accumulated less N and showed a larger C:N ratio than mature leaves. The nitrate reductase activity (NRA) followed the pattern of root: shoot partitioning expected for temperate climate conifers (activity concentrated in roots). However, the presence of NRA even under sole NH4+ nutrition indicates that plants may show constitutive levels of the enzyme, or that low levels of NO3- (possibly formed by contamination of the growth media) can induce leaf NRA. We suggest that A. angustifolia has ammonium as a preferential inorganic N source, and that this preference may favor a more successful establishment in grassland than in forest areas.

Soil NH4 +/NO3 − nitrogen characteristics in primary forests and the adaptability of some coniferous species

In terrestrial ecosystems, soil nutrient regimes at a plant’s living site generally represent the plant’s “nutrition habitat”. Plant species frequently well adapt to their original “nutrition habitat” during a long process of evolution, and the apparent preference for ammonium or nitrate nitrogen source (NH4+ or NO3−) might be an important aspect of the adaptation. Plants typically favor the nitrogen form most abundant in their natural habitats. Nitrate has been recognized as the dominant mineral nitrogen form in most agricultural soils and the main nitrogen source for crops, but it is not usually the case in forest ecosystems. A large number of studies show that the “nutrition habitats” associated with primary forest soils are typically dominated by NH4+ rather than NO3−, generally with NO3− content much lower than NH4+. Low levels of NO3− in these forest soils generally correspond to low net rates of nitrification. The probable reasons for this phenomenon include: 1) nitrification limitations and/or inhibitions caused by lower pH, lower NH4+ availability (autotrophic nitrifiers cannot successfully compete for NH4+ with heterotrophic organisms and plants), or allelopathic inhibitors (tannins or higher-molecular-weight proanthocyanidins) in the soil; or 2) substantial microbial acquisition of nitrate in the soils, which makes net nitrification rates substantially less than gross nitrification rates even though the latter are relatively high.

The influence of partial harvesting and forest floor disturbance on nutrient availability and understory vegetation in boreal mixedwoods

The impacts of partial cut systems on nutrient availability and understory vegetation are poorly understood. To examine these responses, white spruce dominated stands in the boreal mixedwood of Alberta were clear-cut or partial-cut and the forest floor treated by slash burning, mixing, mounding, or scalping in a split-plot design. Soil nutrient availability (ion exchange resin), net N mineralization (in situ incubations), and vegetation (density and cover) responses were assessed. With the exception of higher Mg availability in the clearcuts, differences in nutrient availability were driven by forest floor disturbance and not harvest method. Relative to controls, burning increased availability of NH4+, NO3–, and P, and scalping increased Ca and Mg but diminished K. Controls had low levels of NO3–. The mixing treatment substantially reduced net N mineralization. In terms of vegetation, partial cuts reduced root suckering by Populus spp. (Populus tremuloides Michx., Populus balsamifera L.) relative to clearcuts. Burning and mounding stimulated fireweed (Epilobium angustifolium L.) cover, while scalping increased Populus spp. sucker density. In contrast, mixing largely reduced vegetation establishment, likely because of the destruction of roots and rhizomes and reduced N supply. Nutrient availability and vegetation establishment were more strongly controlled by forest floor disturbance than by partial canopy retention.

LEVELS OF NITROGEN ASSIMILATION IN BROMELIADS WITH DIFFERENT GROWTH HABITS

Bromeliads exhibit several growth habits, ranging from terrestrial to epiphytic and associated shoot and root architectures. Accordingly, they are probably exposed to different sources of supply and forms of nitrogen (N), including mineral and organic. Nitrogen uptake and assimilation could reflect this. We compared the activities of nitrate reductase (NR) and glutamine synthetase (GS) as well as NO3 − contents in plantlets of two bromeliad species. Vriesea fosteriana, a C3saxicolous tank-forming type, and Tillandsia pohliana, an atmospheric CAM epiphyte, were grown in vitro with NO3 −, NH4 + or NH4NO3as the sole N sources (4 mM of N). Nitrate alone was a poor N source to support growth of both plant species but it was effective with NH4 +. Consistently, both bromeliads exhibited very low levels of NO3 − assimilation. The tank-forming species presented GS activity 2.5–3.0 fold higher than T. pohliana. The low GS activity found in T. pohliana compared to V. fosteriana may be related to distinct photosynthetic pathways and may also reflect an adaptation to survival in a nutrient-limited habitat.

Evaluation of 3,4-dimethylpyrazole phosphate as a nitrification inhibitor in a Citrus -cultivated soil

The objectives of this work were to evaluate the inhibitory action on nitrification of 3,4-dimethylpyrazole phosphate (DMPP) added to ammonium sulphate nitrate [(NH4)2SO4 plus NH4NO3; ASN] in a Citrus-cultivated soil, and to study its effect on N uptake. In a greenhouse experiment, 2 g N as ASN either with or without 0.015 g DMPP (1% DMPP relative to NH4+-N) was applied 6 times at 20-day intervals to plants grown in 14-l pots filled with soil. Addition of DMPP to ASN resulted in higher levels of NH4+-N and lower levels of NO3–-N in the soil during the whole experimental period. The NO3–-N concentration in drainage water was lower in the ASN plus DMPP (ASN+DMPP)-treated pots. Also, DMPP supplementation resulted in greater uptake of the fertilizer-N by citrus plants. In another experiment, 100 g N as ASN, either with or without 0.75 g DMPP (1% DMPP relative to NH4+-N) was applied to 6-year-old citrus plants grown individually outdoors in containers. Concentrations of NH4+-N and NO3–-N at different soil depths and N distribution in the soil profile after consecutive flood irrigations were monitored. In the ASN-amended soil, nitrification was faster, whereas the addition of the inhibitor led to the maintenance of relatively high levels of NH4+-N and NO3–-N in soil for longer than when ASN was added alone. At the end of the experiment (120 days) 68.5% and 53.1% of the applied N was leached below 0.60 m in the ASN and ASN+DMPP treatments, respectively. Also, leaf N levels were higher in plants fertilized with ASN+DMPP. Collectively, these results indicate that the DMPP nitrification inhibitor improved N fertilizer efficiency and reduced NO3– leaching losses by retaining the applied N in the ammoniacal form.

Low soil nitrate levels from golf course fairways related to organic matter sink for nitrogen1

Nitrogen (N) is applied to golf course fairways at rates similar to that applied to corn. This appears excessive since N fertilization of corn is approximately equal to the amount of N removed at harvest, while typically no harvest occurs for turf. This study was done to determine soil nitrate (NO3) concentrations from newer and older golf courses and to help determine the fate of fertilizer N. Soil samples were taken every other month in 1995 from two golf courses in southeastern Louisiana to a 3 m depth and from six sites monthly in 1996 to a 1‐m depth. In August 1996, soils were also sampled off of the fairways in areas that were similar to the fairways, but were unfertilized. All soils were analyzed for water‐extractable NO3, and a comparison was made of soil organic matter (OM) and N contents from fertilized and unfertilized areas. Results indicated, with few exceptions, low levels of NO3 throughout the profile, excluding the upper surface soils. Generally, surface soils measured <15 mg kg‐1 NO3‐N while soils at depths >30 cm were <3 mg kg‐1 NO3‐N. The fertilized fairways had 0.151% soil N versus the adjacent unfertilized areas of 0.108% N. The fertilized soils had 1,930 kg more N per 30 cm thick hectare slice than did the unfertilized soils’ equivalent to 10 years of N fertilization. Organic matter was also higher from the fertilized soils than from the unfertilized soils (1.61% versus 1.03%). It appeared much of the N applied to turf throughout the years had been captured by the OM sink. Prior to golf course development, conditions are generally not as conducive for soil OM buildup as compared to the golf‐course regime of adequate N fertilization and no harvests. Some of the high requirement for N of the golf‐course fairways of this study were likely related to the N requirement of a soil OM fraction that grew as the golf course aged.

Mineral Nutrient Composition of Green and White Asparagus Spears

Mineral nutrients were determined in green and white `Jersey Giant' asparagus (Asparagus officinalis L.) spears grown in 1991 near Booneville, Ark. Green spears had higher concentrations of tissue N, K, P, S, Na, and Zn; similar levels of Fe, Al, and Cu; and lower levels of NO3 than white spears grown under opaque plastic rowcovers or under sawdust mulch. Levels of Ca, Mg, and Mn were higher in plastic-grown white spears than in those grown in sawdust. The spear tip contained higher concentrations of K, S, and Cu than the butt. Less NO3, Fe, and Al were in the tip than in the butt. Spear distribution gradients for K, Fe, and Cu were linear, whereas S and NO3 gradients were both linear and quadratic. Nitrogen, P, Ca, Mg, Zn, Al, and Mn levels were influenced by spear production method and spear segment.

NEITHER GREEN NOR WHITE ASPARAGUS SPEARS ARE AFFECTED BY SUPPLEMENTAL NITROGEN

`Jersey Giant' asparagus (Asparagus officinalis L.), grown in an Enders silt loam mineral soil near Booneville, Ark., was given an application of 80 kg/ha of Supplemental nitrogen (N, as NH4N O3) either prior to or after the Cutting season in 1993. Neither N treatment affected spear objective Color, Pigments, soluble solids concentration (SSC), or yield. Supplemental N decreased spear Ca and K levels. Green asparagus had higher levels of total-N, K, S, P, Ca, Mg, Fe, Zn, Al, Mn, and Cu, but lower levels of NO3 than did white asparagus. As the Cutting season progressed, spear SSC, S, Ca, NO3 (NO3 in White spears only), Zn, Mn, and Cu (Cu in white spears Only) levels decreased, While spear K and Al (Al in white spears only) increased on a dry weight basis. Fall residual soil NO3 levels were not affected by N application, but organic matter was lower in soil which received early supplemental N.

Effects of nitrate on influx, efflux and translocation of potassium in young sunflower plants

Influx, efflux and translocation of K+(86Rb) were studied in the roots of sunflower seedlings (Helianthus annuus L. cv. Uniflorus) treated with 0–4.0 mM NO3− during a 9 day growth period or a 24 h pretreatment period. Roots treated with high levels of NO3− absorbed and translocated more K+(86Rb) than seedlings treated with low levels of NO3−. The content of K+ in the shoots was, however, higher in seedlings treated with low levels of NO3−, indicating a low rate of retranslocation of K+ in those plants. K+(86Rb) efflux was highest into the low‐NO3− solutions. All effects on K+(86Rb)‐fluxes were more obvious in high‐K plants than in low‐K plants. The results are discussed in relation to the Dijkshoorn‐Ben Zioni hypothesis for K++ NO3−‐uptake and translocation in plants.

Effects of carbon and nitrogen supplementation on lignin and cellulose decomposition by a Streptomyces.

Effects of nitrogen source and concentration and organic carbon cosubstrates on lignin and cellulose degradation by Streptomyces badius strain 252 were examined using 14C-labeled substrates prepared from Pseudotsuga menziesii twigs. As compared with white-rot fungi, which do not degrade lignin in the absence of a readily metabolizable carbon cosubstrate, degradation of a milled-wood lignin occurred in a minimal medium, although degradation by S. badius was greatly enhanced when organic nitrogen and an organic carbon cosubstrate were added to the medium. Lignin degradation was greatest in the presence of high levels of organic nitrogen. Further enhancement of lignin and cellulose degradation occurred in a medium containing organic nitrogen supplemented with low levels of NO3-. The specific effects of inorganic nitrogen on lignocellulose degradation by S. badius in an otherwise optimal medium included both enhancement and inhibition of lignin or cellulose degradation depending on the source and concentration of inorganic nitrogen used. These effects were distinctly different from those observed with white-rot fungi and were shown to be specific ion effects on polymer degradation and not simply a salt concentration effect on cellular growth.

EFFECTS OF CERTAIN NEMATICIDES ON SOIL NITROGEN, SOIL NITRIFIERS, AND POPULATIONS OF PRATYLENCHUS PENETRANS IN FLUE-CURED TOBACCO

Field experiments were conducted in 1973 and 1974 on Fox loamy sand to study the effects of Telone (1,3-dichloropropene and related C3 hydrocarbons), Telone C (1,3-dichloropropene and related C3 hydrocarbons 85%, and chloropicrin 15%), Vorlex (1,3-dichloropropene and related C3 hydrocarbons 80%, and methyl isothiocyanate 20%), and the non-fumigant nematicide oxamyl (methyl N′,N′-dimethyl-N-[(methyl-carbamoyl)oxy]-1-thiooxamimidate) on soil nitrifying bacteria, soil nitrogen, and Pratylenchus penetrans (Cobb) Filip, and Stek. 1941 in flue-cured tobacco. Chloropicrin and triazophos (1-phenyl-3-(0-0-diethylthionophosphoryl)-1, 2, 4-triazole), a non-fumigant, were also included in 1974. Soil treated with fumigant nematicides was higher in NH4+-N than untreated soil or soil treated with non-fumigant nematicides. Lower levels of NO3−-N were found in the soil 37 days after fumigation with Telone or Telone C and 28 days with Vorlex. Fumigant nematicides increased total mineralization, (NH4+ + NO3−)-N, of organic nitrogen in the soil; the effect lasted longer with Telone C and chloropicrin. Nitrosomonas spp. were higher in Telone- or Telone C-treated plots at 4 wk after fumigation and higher in all nematicide plots at 8 wk. Nitrobacter spp. were higher with Vorlex and oxamyl than in the check plots at 4, 6, and 8 wk after fumigation. Nematicides reduced the population of P. penetrans in the soil throughout the season in 1973 but control was less consistent in 1974. Oxamyl and triazophos gave good control of nematodes in roots of flue-cured tobacco. All nematicides tested gave an increase in yield of tobacco in 1973 but no significant increases were obtained in 1974.