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1.
One-year-old seedlings of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) are not colonized with ectomycorrhizal (EM) fungi, but often colonized with arbuscular mycorrhizal (AM) fungi. The AM fungi could be important for nutrient acquisition in Chinese fir seedlings. Previous studies show that feedbacks between aboveground and belowground plant tissues play a fundamental role in controlling the interaction between plants and AM fungi. Our results indicate significant feedback in seedlings grown on shrubland soils, but not on plowed soils. The amounts of sugar in fir leaves in the shrubland soils were significantly lower than those in plowed soils. Leaf zinc (Zn) and nitrogen (N) concentrations were significantly higher in seedlings in shrubland soils than in plowed soils. In mycorrhizal seedlings growing in shrubland soils, leaf N:P ratios were significantly higher than those in plowed soils, likely because of enhanced N absorption through AM-mediated process. Leaf N:P ratios in seedlings grown on plowed soils were below the threshold levels, because of low metabolic activity of feedback in AM-mediated process. The results suggested that the presence of feedback between Chinese fir seedlings and AM fungi should be benefit in transplanting Chinese fir seedlings.  相似文献   

2.
ABSTRACT

Plant nitrogen (N)-acquisition strategy affects soil N availability, community structure, and vegetation productivity. Cultivated grasslands are widely established to improve degraded pastures, but little information is available to evaluate the link between N uptake preference and forage crop biomass. Here an in-situ 15N labeling experiment was conducted in the four cultivated grasslands of Inner Mongolia, including two dicots (Medicago sativa and Brassica campestris) and two monocots (Bromus inermis and Leymus chinensis). Plant N uptake rate, shoot- and root biomass, and concentrations of soil inorganic-N and microbial biomass-N were measured. The results showed that the root/shoot ratios of the dicots were 2.6 to 16.4 fold those of the monocots. The shoot N concentrations of the dicots or legumes were 40.6% to 165% higher than those of the monocots or non-legumes. The four forage crops in the cultivated grassland preferred to uptake more NO3?-N than NH4+-N regardless of growth stages, and the NH4+/NO3? uptake ratios were significantly lower in the non-legumes than in the legumes (p < 0.05). Significant differences in the NH4+-N rather than NO3?-N uptake rate were observed among the four forages, related to plant functional types and growth stages. The NH4+ uptake rate in the perennial forages exponentially decreased with the increases in shoot-, root biomass, and root/shoot ratio. Also, the plant NH4+/NO3? uptake ratio was positively correlated with soil NH4+/NO3? ratio. Our results suggest that the major forage crops prefer to absorb soil NO3?-N, depending on soil inorganic N composition and belowground C allocation. The preferential uptake of NO3?-N by forages indicates that nitrate-N fertilizer could have a higher promotion on productivity than ammonium-N fertilizer in the semi-arid cultivated grassland.  相似文献   

3.
Relay strip intercropping of soybean has been widely developed in the southwest of China to secure China's soybean production. However, due to the shading from maize, soybean plants are thin and have a poor root system. Uniconazole is a plant-growth retardant that could enhance root vigor; increase root length, root volume, and root dry weight; and affect nitrogen (N) metabolism. To understand the effects of uniconazole on the root growth and N-transfer metabolism of soybean seedlings under relay strip intercropping, the changes in some morphological characteristics of root, dry-matter weight, root vigor, nitrate (NO3 ?)-N, ammonium (NH4 +)-N, and amino acid of xylem sap after seed treatment with uniconazole powder (0, 2, 4, and 8 mg kg?1 seed) were investigated. Main root length, total lateral root lengths, first lateral root numbers, root nodule numbers, root vigor together with bleeding sap, bleeding sap–top ratio, root dry weight, and root/shoot ratio were increased, indicating uniconazole improved soybean root system in relay strip intercropping. Uniconazole powder treatment could increase NO3 ?-N, NH4 +-N, and total amino acid of xylem sap, to increase the potential of leaf and root N reduction and assimilation, and increase of leaf and root N contents. Thus, results suggested that uniconazole treatment can improve root growth and N transfer mechanism of soybean to support its further growth.  相似文献   

4.

Purpose

We investigated the effects of weed control and fertilization at early establishment on foliar stable carbon (δ13C) and nitrogen (N) isotope (δ15N) compositions, foliar N concentration, tree growth and biomass, relative weed cover and other physiological traits in a 2-year old F1 hybrid (Pinus elliottii var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Barr. ex Golf.)) plantation grown on a yellow earth in southeast Queensland of subtropical Australia.

Materials and methods

Treatments included routine weed control, luxury weed control, intermediate weed control, mechanical weed control, nil weed control, and routine and luxury fertilization in a randomised complete block design. Initial soil nutrition and soil fertility parameters included (hot water extractable organic carbon (C) and total nitrogen (N), total C and N, C/N ratio, labile N pools (nitrate (NO3 ?) and ammonium (NH4 +)), extractable potassium (K+)), soil δ15N and δ13C. Relative weed cover, foliar N concentrations, tree growth rate and physiological parameters including photosynthesis, stomatal conductance, photosynthetic nitrogen use efficiency, foliar δ15N and foliar δ13C were also measured at early establishment.

Results and discussion

Foliar N concentration at 1.25 years was significantly different amongst the weed control treatments and was negatively correlated to the relative weed cover at 1.1 years. Foliar N concentration was also positively correlated to foliar δ15N and foliar δ13C, tree height, height growth rates and tree biomass. Foliar δ15N was negatively correlated to the relative weed cover at 0.8 and 1.1 years. The physiological measurements indicated that luxury fertilization and increasing weed competition on these soils decreased leaf xylem pressure potential (Ψxpp) when compared to the other treatments.

Conclusions

These results indicate how increasing N resources and weed competition have implications for tree N and water use at establishment in F1 hybrid plantations of southeast Queensland, Australia. These results suggest the desirability of weed control, in the inter-planting row, in the first year to maximise site N and water resources available for seedling growth. It also showed the need to avoid over-fertilisation, which interfered with the balance between available N and water on these soils.  相似文献   

5.
Buzek  F.  Černý  J.  Pačes  T. 《Water, air, and soil pollution》1998,105(1-2):155-164
The effects of atmospheric deposition on N cycling in acidified soils were studied at three spruce and one beech forested sites in the Czech Republic. Nitrogen content and δ15N were monitored in bulk and throughfall precipitation, needles, leaves, soils and soil solutions. Changes in soil NO3 - production, effect of admixing of atmospheric N in spruce forest and N consumption in deciduous forest are described using changes in 15N fractionation of mineralized N in soil. Admixing of atmospheric NH4+ can be identified at low concentrations of exchangeable NH4 +. The δ15N ratio of atmospheric NO3 - input is on average by 2‰ less negative than the δ5N ratio in soil water; admixing changes the δ15N of soil NO3 - detected in lysimeters.  相似文献   

6.
A laboratory-based aerobic incubation was conducted to investigate nitrogen(N) isotopic fractionation related to nitrification in five agricultural soils after application of ammonium sulfate((NH4)2SO4). The soil samples were collected from a subtropical barren land soil derived from granite(RGB),three subtropical upland soils derived from granite(RQU),Quaternary red earth(RGU),Quaternary Xiashu loess(YQU) and a temperate upland soil generated from alluvial deposit(FAU). The five soils varied in nitrification potential,being in the order of FAU YQU RGU RQU RGB. Significant N isotopic fractionation accompanied nitrification of NH+4. δ15N values of NH+4 increased with enhanced nitrification over time in the four upland soils with NH+4 addition,while those of NO-3 decreased consistently to the minimum and thereafter increased. δ15N values of NH+4 showed a significantly negative linear relationship with NH+4-N concentration,but a positive linear relationship with NO-3-N concentration. The apparent isotopic fractionation factor calculated based on the loss of NH+4 was 1.036 for RQU,1.022 for RGU,1.016 for YQU,and 1.020 for FAU,respectively. Zero- and first-order reaction kinetics seemed to have their limitations in describing the nitrification process affected by NH+4 input in the studied soils. In contrast,N kinetic isotope fractionation was closely related to the nitrifying activity,and might serve as an alternative tool for estimating the nitrification capacity of agricultural soils.  相似文献   

7.
Vermicompost, a byproduct of earthworm digestion of organic solid waste is receiving attention as a peat substitute in the production of plug seedling media. We aimed to test the effects of adding nitrogen to vermicompost on the morphological development of tomato seedlings. Nursery experiments on tomato seedlings were carried out in the greenhouse. Urea at 0.00 kg/m3, 0.25 kg/m3, 0.50 kg/m3, and 1.00 kg/m3 was added to vermicompost and to the vermicompost-vermiculite (at a volume ratio of 4:1) mixture. Results showed that (1) Nitrogen application at different rates to the vermicompost significantly increased the strong seedling index (SSI) at the middle (T1) and late (T2) seedling growth stages. Besides, nitrogen application significantly increased concentrations of available nitrogen (available-N) at the beginning of seedling cultivation (T0) and nitrate nitrogen (NO3?-N) at T2 in vermicompost. (2) Adding nitrogen to vermicompost significantly increased the number of root tips at T1 and T2 and the root volume at T2. And it significantly decreased the electrical conductivity (EC), total N (TN), available N, ammonium N (NH4+-N), and NO3?-N at T1 and T2. (3) Adding nitrogen to the vermicompost-vermiculite mixture significantly increased the root/shoot ratio, and SSI at T1 and T2. And it significantly increased the pH and reduced the EC at T1 and the available-N, NH4+-N, and NO3?-N at T2. In short, adding nitrogen (0.5～1.0 kg/m3 urea) to vermicompost improved the shoot and root morphological development of tomato seedlings, as well as the biomass accumulation and allocation. Adding nitrogen to the vermicompost-vermiculite mixture further promoted the development of tomato seedlings.  相似文献   

8.
The effects of nitrogen (N) forms (ammonium- or nitrate-N) on plant growth under salinity stress [150 mmol sodium chloride (NaCl)] were studied in hydroponically cultured cotton. Net fluxes of sodium (Na+), ammonium (NH4+), and nitrate (NO3?) were also determined using the Non-Invasive Micro-Test Technology. Plant growth was impaired under salinity stress, but nitrate-fed plants were less sensitive to salinity than ammonium-fed plants due mainly to superior root growth by the nitrate-fed plants. The root length, root surface area, root volume, and root viability of seedlings treated with NO3-N were greater than those treated with NH4-N with or without salinity stress. Under salinity stress, the Na+ content of seedlings treated with NO3-N was lower than that in seedlings treated with NH4-N owing to higher root Na+ efflux. A lower net NO3? efflux was observed in roots of nitrate-fed plants relative to the net NH4+ efflux from roots of ammonium-fed plants. This resulted in much more nitrogen accumulation in different tissues, especially in leaves, thereby enhancing photosynthesis in nitrate-fed plants under salinity stress. Nitrate-N is superior to ammonium-N based on nitrogen uptake and cotton growth under salinity stress.  相似文献   

9.
Aerobic incubations to estimate net nitrogen (N) mineralization typically involve periodic leaching of soil with 0.01 M calcium chloride (CaCl2), so as to remove mineral N that would otherwise be subject to immobilization. A study was conducted to evaluate the accuracy of leaching for analysis of exchangeable ammonium (NH4+)-N and nitrate + nitrite (NO3?+ NO2–)-N, relative to conventional extractions using 2 M potassium chloride (KCl). Ten air-dried soils were used, five each from Illinois and Brazil, that had been amended with NH4+-N (1 g kg?1) and NO3–-N (0.6 g kg?1). Both methods were in good agreement for inorganic N analysis of the Brazilian Oxisols, whereas leaching was significantly lower by 12–48% in recovering exchangeable NH4+-N from Illinois Alfisols, Mollisols, and Histosols. The potential for underestimating net N mineralization was confirmed by a 12-wk incubation experiment showing 9–86% of mineral N recoveries from three temperate soils as exchangeable NH4+.  相似文献   

10.
Purpose

Sustainable management of riparian zone soils is required to ensure the health of natural ecosystems and maintenance of soil nitrogen (N) pools and soil N cycling. However, the effect of revegetation type and age on soil N pools remains poorly understood.

Materials and methods

This study compiled data from published articles to understand the effects of revegetation types and age on soil total N (TN) and soil inorganic N (NH4+-N, and NO3?-N) using a meta-analysis. We extracted 645 observations from 52 published scientific articles.

Results and discussion

The revegetation of riparian zones led to a significant increase of soil TN (mean effect size: 11.5%; 95% CI: 3.1% and 20.6%). Woodland increased soil TN significantly by 14.0%, which was associated with the presence of N fixing species and high litter inputs. Soil NH4+-N concentration significantly increased (mean effect size: 20.1%; 95% CI: 15.1% and 25.4%), whereas a significant decrease in soil NO3?-N (mean effect size: ? 21.5%; 95% CI: ? 15.0% and ? 27.5%) was observed. Of the revegetation types considered in this paper, NO3?-N concentration in soil followed the order: grassland < shrubland < woodland, suggesting that woodland might be more efficient in soil NO3?-N retention than grassland. The high plant N uptake and accelerated NO3?-N leaching in grassland could be related to the decreased soil NO3?-N in grassland compared with other revegetation types. Revegetation significantly decreased soil moisture by (mean effect size: ? 7.9%; 95% CI: ? 3.3% and ? 12.2%) compared with the control, which might be associated with the selection of exotic species as dominant vegetation in the riparian zone. Soil TN increased in revegetation ages between 10 and 40 years following revegetation and was related to increased soil organic carbon inputs within those ages following the establishment.

Conclusions

This study provides insight into influence of different vegetation types and age on soil N pools and soil moisture. This study also highlights the importance of revegetation in riparian zones to increase soil TN.

  相似文献   

11.
The incidence and severity of take-all disease, due to Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici Walker, was observed on spring barley plants growing in soil in two glasshouse experiments. Soil amendments of NH+4-N significantly increased the number of diseased plants and roots during the first month after germination in comparison with controls unamended with N (P < 0.05). No significant difference in the incidence of take-all disease was detected between more mature barley plants growing in soil amended with either NH+4 or NO?3-N and unamended controls. The least take-all disease in 3 month-old barley plants was observed when N was supplied as foliar sprays of urea at 0.5 mg N kg?1 soil (P < 0.01). There was no significant correlation between the degree of infection and the NH+4-N to NO?3-N ratio in the rhizosphere soil  相似文献   

12.
不同沟灌方式下玉米根区矿物氮迁移动态研究   总被引：1，自引：0，他引：1  
为探索交替隔沟灌溉下玉米根区矿物氮分布规律, 通过遮雨棚内微区试验, 研究了常规沟灌、交替隔沟灌和固定隔沟灌3 种沟灌方式对玉米根区硝态氮、铵态氮迁移的影响。结果表明: 交替隔沟灌溉根区硝态氮等值线和常规沟灌相似, 沟内硝态氮含量基本沿垄的中心对称分布。固定隔沟灌溉的湿润沟内硝态氮含量小于干燥沟, 施氮后非灌水沟硝态氮保持较高水平。收获时交替隔沟灌溉的根区硝态氮残留量比常规灌溉略高。与硝态氮分布相比, 铵态氮在根区土壤中的含量很小, 3 种沟灌方式在沟和垄中的铵态氮含量没有明显差异。  相似文献   

13.
Purpose

This study examined the usefulness of 15N natural abundance (δ15N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning.

Materials and methods

In situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L?1 NO3?-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ15N of NH4+-N and NO3?-N in the top 5 cm soil before and after the incubation, and δ15N of NO3?-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes.

Results and discussion

The significant decrease in δ15N of NH4+-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ15N of NH4+-N and significant increase in δ15N of NO3?-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes.

Conclusions

The δ15N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ15N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes.

  相似文献   

14.
Root development responds not only to the quantity of inorganic nitrogen in the rhizosphere, but to its form, NH4+ or NO3?. Root growth of tomato showed a hyperbolic response to soil levels of inorganic nitrogen: very few roots were found in soil blocks depleted in inorganic nitrogen, roots proliferated as soils increased to 2 μg NH4+-N g?1 soil or 6 μg NO3?-N g?1 soil, and root growth declined in soils with the higher levels of inorganic nitrogen. High NH4+ concentrations inhibited root growth, but low concentrations promoted the development of an extensive, fine root system. Supply with NO3? as the sole nitrogen source led to a more compact root system. These differences in root morphology under NH4+ and NO3? nutrition may be mediated through pH. Rice and maize roots absorbed NH4+ most rapidly right at the apex and appeared to assimilate this NH4+ in the zone of elongation. During NH4+ assimilation, root cells must release protons, and the resulting acidification around the walls of cells in this region should stimulate root extension. By contrast, NO3? absorption reached a maximum in the maturation zone of rice and maize roots, and this NO3? was probably assimilated in more basal regions. Absorption of NO3? requires proton efflux, whereas NO3? assimilation requires proton influx. The net result under NO3? nutrition was only subtle shifts in rhizosphere pH that probably would not influence root elongation. The signal through which roots detect changes in rhizosphere NH4+ and NO3? levels is still obscure. It is proposed that a product of nitrogen metabolism such as nitric oxide serves as a signal.  相似文献   

15.
N2O emissions from soils treated with NH4+-N under aerobic conditions in the laboratory were 3- to 4-fold higher than those from controls (no extra N added) or when NO3?-N was added. Although the emission of N2O-N in these field and laboratory experiments represented only 0.1–0.8% of the applied fertilizer NH4+-N and are therefore not significant from an agronomic standpoint, these studies have conclusively demonstrated that the oxidation of applied ammoniacal fertilizers (nitrification) could contribute significantly to the stratospheric N2O pool.Like N-serve, acetylene was shown to be a potent inhibitor of nitrification as it stopped the oxidation of NH4+-N to (NO3+-N + NO2?)-N and hence reduced the evolution of N2O from nitrification within 60 min after its addition.Although high amounts of NO3?-N were present, the rate of denitrification was very low from soils with moisture up to 60% saturation. The further increase in the degree of saturation resulted in several-fold increase of denitrification which eventually became the predominant mechanism of gaseous N losses under anaerobic conditions.  相似文献   

16.

Purpose

This study investigated how nitrogen (N) nutrition and key physiological processes varied under changed water and nitrogen competition resulting from different weed control and fertilisation treatments in a 2-year-old F1 hybrid (Pinus elliottii Engelm var. elliottii?×?P. caribaea var. hondurensis Barr. ex Golf.) plantation on a grey podzolic soil type, in Southeast Queensland.

Materials and methods

The study integrated a range of measures including growth variables (diameter at ground level (DGL), diameter at breast height (DBH) and height (H)), foliar variables (including foliar N concentration, foliar δ13C and δ15N) and physiological variables (including photosynthesis (An), stomatal conductance (gs), transpiration (E), intrinsic water use efficiency (WUEi) (A/gs) and xylem pressure potential (ΨXPP)) to better understand the mechanisms influencing growth under different weed control and fertilisation treatments. Five levels of weed control were applied: standard (routine), luxury, intermediate, mechanical and nil weed control, all with routine fertilisation plus an additional treatment, routine weed control and luxury fertilisation. Relative weed cover was assessed at 0.8, 1.1 and 1.6 years after plantation establishment to monitor the effectiveness of weed control treatments. Soil investigation included soil ammonium (NH4 +-N), nitrate (NO3 ?-N), potentially mineralizable N (PMN), gravimetric soil moisture content (MC), hot water extractable organic carbon (HWETC), hot water extractable total N (HWETN), total C, total N, stable C isotope composition (δ13C), stable N isotope composition (δ15N), total P and extractable K.

Results and discussion

There were significant relationships between foliar N concentrations and relative weed cover and between tree growth and foliar N concentration or foliar δ15N, but initial site preparation practices also increased soil N transformations in the planting rows reducing the observable effects of weed control on foliar δ15N. A positive relationship between foliar N concentration and foliar δ13C or photosynthesis indicated that increased N availability to trees positively influenced non-stomatal limitations to photosynthesis. However, trees with increased foliar N concentrations and photosynthesis were negatively related to xylem pressure potential in the afternoons which enhanced stomatal limitations to photosynthesis and WUEi.

Conclusions

Luxury and intermediate weed control and luxury fertilisation positively influenced growth at early establishment by reducing the competition for water and N resources. This influenced fundamental key physiological processes such as the relationships between foliar N concentration, A n, E, gs and ΨXPP. Results also confirmed that time from cultivation is an important factor influencing the effectiveness of using foliar δ15N as an indicator of soil N transformations.
  相似文献   

17.
High yield agricultural systems, such as high tunnel (HT) vegetable production, require a large supply of soil nutrients, especially nitrogen (N). Compost is a common amendment used by HT growers both to supply nutrients and to improve physical and biological soil properties. We examined commercially-available composts and their effects on soil N, plant N uptake, and tomato yield in HT cultivation. In addition, a laboratory study examined N and carbon (C) mineralization from the composts, and the usefulness of compost properties as predictors of compost N mineralization was assessed under field and laboratory conditions. The field study used a randomized complete block design with four replications to compare four compost treatments (all added at the rate of 300 kg total N ha?1) with unamended soil and an inorganic N treatment (110 kg N ha?1). Tomatoes were grown in Monmouth, Maine during the summers of 2013 and 2014. Compost NO3?-N and NH4+-N application rates were significantly correlated with soil NO3?-N and NH4+-N concentrations throughout the growing season. Marketable yield was positively correlated with compost total inorganic N and NO3?-N in both years, and with NH4+-N in 2014. There were no significant differences among composts in percentage of organic N mineralized and no correlations were observed with any measured compost property. In the laboratory study, all compost-amended soils had relatively high rates of CO2 release for the initial few days and then the rates declined. The compost-amended soils mineralized 4%–6% of the compost organic N. This study suggested compost inorganic N content controls N availability to plants in the first year after compost application.  相似文献   

18.
Indirect evidence of the nitrogen (N) status of tropical forests strongly suggests that in heavily weathered soils under old-growth lowland tropical forests nitrogen is in relative excess. However, within the lowland forests of the Amazon basin, there is substantial evidence that soil texture influences soil NH4+ and NO3? concentrations and hence possibly N availability and retention in the soil. Here, we evaluate the soil N status of two heavily weathered soils which contrast in texture (sandy versus clay Oxisol). Using 15N pool dilution, we quantified gross rates of soil N cycling and retention. We also measured the δ15N signatures from the litter layer down to 50-cm depth mineral soil and calculated the overall 15N enrichment factor (ε) for each soil type. The clay soil showed high gross N mineralization and nitrification rates and a high overall 15N enrichment factor, signifying high N losses. The sandy soil had low gross rates of N cycling and 15N enrichment factor, manifesting a conservative soil N cycling. Faster turnover rates of NH4+ compared to NO3? indicated that NH4+ cycles faster through microorganisms than NO3?, possibly contributing to better retention of NH4+ than NO3?. However this was opposite to abiotic retention processes, which showed higher conversion of NO3? to the organic N pool than NH4+. Our combined results suggest that clay Oxisol in Amazonian forest have higher N availability than sandy Oxisol, which will have important consequences for changes in soil N cycling and losses when projected increase in anthropogenic N deposition will occur.  相似文献   

19.
In many coastal areas of Louisiana, surface water quality is deteriorating rapidly due to elevated nutrient input from agricultural, domestic and industrial sources. This study investigates the potential use of natural abundance variations in 15N/14N ratios for identification and tracing surface water inorganic N sources. Surface water samples were collected from streams and point sources in Louisiana and analyzed for NH4 +-N, NO3 ?-N and associated 15N/14N (δ15N ‰) concentrations. Ammonium-N from domestic sewage and industrial discharge point sources was found to have distinct δ15N ranges. Domestic sewage discharge into a slow flowing stream was traced for about 30 km downstream using 15N/14N ratios. At the sewage point source NH4 +-δ15N values averaged +43%o and increased linearly to +162‰ with distance from the discharge. In a larger stream with a greater flow velocity the NH4 +-δ15N surface water signature of an industrial discharge source was identifiable for approximately 1 km from the point source. Surface water NO3 ?-°15N values generally ranged from +1 to +99‰ and no significant association was observed between δ15N values with distance from the domestic sewage and industrial point sources. The discrete NH4 +-δ15N signatures of domestic sewage and industrial point sources compared to downstream surface water NH4 +-δ15N values suggest that N isotopic ratios have the potential to be used as tracers in surface waters contaminated with inorganic N.  相似文献   

20.
Optimal fertilizer nitrogen (N) rates result in economic yield levels and reduced pollution. A soil test for determining optimal fertilizer N rates for wheat has not been developed for Quebec, Canada, or many other parts of the world. Therefore, the objectives were to determine: 1) the relationship among soil nitrate (NO? 3)- N, soil ammonium (NH + 4)- N and N fertilizer on wheat yields; and 2) the soil sampling times and depths most highly correlated with yield response to soil NO? 3-N and NH + 4-N. In a three year research work, wet and dried soil samples of 0- to 30- and 30- to 60-cm depths from 20 wheat fields that received four rates of N fertilizer at seeding and postseeding (plants 15 cm tall) were analyzed for NH + 4-N and NO? 3 -N using a quick-test (N-Trak) and a standard laboratory method. Wheat yield response to N fertilizer was limited, but strong to soil NO? 3-N.  相似文献   

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