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1.
Abstract

Long‐term field experiments are the most suitable tools for determining the optimal nutrient‐supplying technologies that contribute to sustainable agriculture. Under certain environmental conditions (low precipitation, deep groundwater table, negative water balance), part of the applied nitrogen (N) can be found in the soil profile for a longer period and provide N nutrition for crops. A long‐term field experiment has been running at Nagyhörcsök in Hungary since 1973. The nitrogen–phosphorus–potassium (NPK) application rates follow the overall nutrient‐supplying categories (weak, medium, adequate, excessive) by the main nutrients and their combinations. The seasonal dynamics of exchangeable NH4 and NO3 were followed in 1983 and 2003. From certain treatments, two parallel average samples (20–20 subsamples were mixed to get average composite samples by plots) were collected 19 times from March through November from three soil layers. There was no difference in NH4‐N between years, and its seasonal fluctuation was slight in both years, whereas there was an increase in NO3‐N in accordance with the applied N rates. No significant difference occurred in the NO3‐N of the N0P0K0 and the N1P1K1 treatments during both years. A significantly higher NO3‐N content was observed in the higher rate nutrient treatments. Both soil N forms were higher in 1983 than in 2003. Based on the experimental results, the fate and behavior of the surplus N in the soil can be characterized and the residual amount can be taken into account during the calculation of the N‐fertilization demand of arable crops in relation to the N‐fertilizer advisory system.  相似文献   

2.
Abstract

Both nitrogen (N) deposition and biochar can affect the emissions of nitrous oxide (N2O), carbon dioxide (CO2) and ammonia (NH3) from different soils. Here, we have established a simulated wet N deposition experiment to investigate the effects of N deposition and biochar addition on N2O and CO2 emissions and NH3 volatilization from agricultural and forest soils. Repacked soil columns were subjected to six N deposition events over a 1-year period. N was applied at rates of 0 (N0), 60 (N60), and 120 (N120) kg Nh a?1 yr?1 without or with biochar (0 and 30 t ha?1 yr?1). For agricultural soil, adding N increased cumulative N2O emissions by 29.8% and 99.1% (p < 0.05) from the N60 and N120 treatments, respectively as compared to without N treatments, and N120 emitted 53.4% more (p < 0.05) N2O than the N60 treatment; NH3 volatilization increased by 33.6% and 91.9% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 43.6% more (p < 0.05) NH3 than N60; cumulative CO2 emissions were not influenced by N addition. For forest soil, adding N significantly increased cumulative N2O emissions by 141.2% (p < 0.05) and 323.0% (p < 0.05) from N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 75.4% more (p < 0.05) N2O than N60; NH3 volatilization increased by 39.0% (p < 0.05) and 56.1% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and there was no obvious difference between N120 and N60 treatments; cumulative CO2 emissions were not influenced by N addition. Biochar amendment significantly (p < 0.05) decreased cumulative N2O emissions by 20.2% and 25.5% from agricultural and forest soils, respectively, and increased CO2 emissions slightly by 7.2% and NH3 volatilization obviously by 21.0% in the agricultural soil, while significantly decreasing CO2 emissions by 31.5% and NH3 volatilization by 22.5% in the forest soil. These results suggest that N deposition would strengthen N2O and NH3 emissions and have no effect on CO2 emissions in both soils, and treatments receiving the higher N rate at N120 emitted obviously more N2O and NH3 than the lower rate at N60. Under the simulated N deposition circumstances, biochar incorporation suppressed N2O emissions in both soils, and produced contrasting effects on CO2 and NH3 emissions, being enhanced in the agricultural soil while suppressed in the forest soil.  相似文献   

3.
Abstract

A pot experiment was conducted under natural climatic conditions to study the effect of low doses of gamma irradiation (0, 5, 10, and 20 Gy) on the performance of winter chickpea (Cicer arietinum L.) in the presence of increased supply of 15N labeled ammonium sulfate (0, 20, 50, and 100 kg N ha‐1). Presowing seed irradiation produced a significant increase in dry matter production (up to 3 6%) and total nitrogen yield (up to 45%). The stimulative effect of irradiation was more pronounced with the application of NH4 +‐N fertilizer. Seed irradiation increased the amount of N2‐fixation by 8–61% depending on the dose and level of NH4 +‐N fertilizer rate. A 10 Gy was found to be the optimal irradiation dose for enhancing N2‐fixation. High levels of NH4 +‐N decreased the percentage and the amount of N2‐fixation, but did not affect nodule formation. However, the presowing 10 Gy irradiation dose reduced the negative effect of ammonia‐N fertilizer on N2‐fixation. Therefore, we recommend irradiating chickpea seeds with a 10 Gy dose before planting in soil containing high levels of mineral nitrogen to reduce its negative effect on N2‐fixation.  相似文献   

4.
Abstract

Seven rice soils varying in texture, pH, organic matter and total nitrogen content were extracted with 1N and 2N KCl, 1N and 2N Nacl, 10% Nacl at pH 2.5, N CH3 CooNa at pH 3.0, and Morgan's reagent using a soil: solution ratio of 1:10. The ammonium in the extracts was determined by steam distillation with MgO.

The normality of KCl or Nacl had no significant effect on the amount of NH4 + ‐N extracted but KCl proved a better extractant than Nacl. However, Nacl at pH 2.5 generally extracted significantly higher amounts of NH4 + ‐N as compared to the neutral salt solution. N CH3 CooNa at pH 3.0 did not extract more NH4 + than Morgan's reagent. Overall, KCl appeared to be better than Nacl; Nacl at pH 2.5 N CH3 CooNa and Morgan's reagent were either equally effective or better for some of the soils as compared to KCl. However, when recovery of the known amount of NH4 +‐N applied to soils was used as a criterion, the efficiency of these chemicals were in the following descending order: KCl > NaCl, pH 2.5 > NaCl > CH3CooNa, pH 3.0 > Morgan's reagent.  相似文献   

5.
Abstract

Determination of soil aluminum (Al), ammonium‐nitrogen (NH4‐N), and nitrate‐nitrogen (NO3‐N) is often needed from the same soil samples for lime and fertilizer recommendations, but Al has to be extracted and quantified separately from NH4‐N and NO3‐N according to present methods. The objective of this study was to develop a reliable method for simultaneous analyses of soil Al, NH4‐N and NO3‐N using a Flow Injection Autoanalyzer. Thirty‐five soil samples from different locations with wide ranges of extractable Al, NH4‐N and NO3‐N were selected for this study. Aluminum, NH4‐N and NO3‐N were extracted by both 1 M and 2 M potassium chloride (KCl), and quantified using a LACHAT Flow Injection Autoanalyzer simultaneously and separately. One molar KCl was found to be a suitable extractant for all three compounds when compared to 2 M KCl. The 1 M KCl extract proposed could aid in decreasing the costs associated with simultaneous NH4‐N, NO3‐N, and Al analyses. Results of those three compounds analyzed simultaneously were not statistically different from those analyzed separately in 1 M KCl solution. This new procedure of simultaneous determination of NH4‐N, NO3‐N, and Al increases efficiency and reduces cost for soil test laboratories and laboratory users.  相似文献   

6.
Abstract

For Southeastern forest soils amounts of P, K, Ca, Mg, and Mn extracted by 0.05 N HCl + 0.025 N H2SO4 (double‐acid) were significantly correlated with amounts extracted by 0.2 N NH4Cl + 0.2 N HOAc + 0.015 N + NH4F + 0.012 N HCl (new‐Mehlich). The new‐Mehlich consistently removed more nutrients than the double acid.

Both P and Mn extracted by the two solutions were significantly correlated with their concentrations in the foliage of loblolly pine (Pinus taeda L.).  相似文献   

7.
Abstract

Microbial nitrification and denitrification are responsible for the majority of soil nitrous (N2O) emissions. In this study, N2O emissions were measured and the abundance of ammonium oxidizers and denitrifiers were quantified in purple soil in a long-term fertilization experiment to explore their relationships. The average N2O fluxes and abundance of the amoAgene in ammonia-oxidizing bacteria during the observed dry season were highest when treated with mixed nitrogen, phosphorus and potassium fertilizer (NPK) and a single N treatment (N) using NH4HCO3as the sole N source; lower values were obtained using organic manure with pig slurry and added NPK at a ratio of 40%:60% (OMNPK),organic manure with pig slurry (OM) and returning crop straw residue plus synthetic NH4HCO3fertilizer at a ratio of 15%:85% (SRNPK). The lowest N2O fluxes were observed in the treatment that used crop straw residue(SR) and in the control with no fertilizer (CK). Soil NH4+provides the substrate for nitrification generating N2O as a byproduct. The N2O flux was significantly correlated with the abundance of the amoA gene in ammonia-oxidizing bacteria (r = 0.984, p < 0.001), which was the main driver of nitrification. During the wet season, soil nitrate (NO3?) and soil organic matter (SOC) were found positively correlated with N2O emissions (r = 0.774, p = 0.041 and r = 0.827, p = 0.015, respectively). The nirS gene showed a similar trend with N2O fluxes. These results show the relationship between the abundance of soil microbes and N2O emissions and suggest that N2O emissions during the dry season were due to nitrification, whereas in wet season, denitrification might dominate N2O emission.  相似文献   

8.
Abstract

Rice (Oryza sativaL. CV. Lemont) was grown on 19 soils, and eight extractants were evaluated for determining the availability of Cu to rice plants. Correlation analyses were employed as criteria for evaluating methods that would provide the best index of Cu availability. The order of removal of Cu from soils was: 0.5NHC1 + 0.05NA1C13> 0.5NHNO3> 0.5 N HC1 > EDTA + NH4OAc > 0.1NHC1 > EDTA + (NH4)2CO3? DTPA‐TEA, pH 7.3 >>> 1 N NH40Ac, pH 4.8.

Uptake of Cu by rice plants was significantly correlated with soil Cu. Among the eight extractants evaluated, Cu extracted with DTPA‐TEA, pH 7.3 was better related to the concentration (r = 0.563 ) and uptake (r = 0.673 ) of Cu by rice plants grown on the soils with different chemical and physical properties.

A significant negative correlation was found between the concentration of Cu in rice plants and the organic matter content of the soils. Each one percent increase in the organic matter of the soils resulted in a corresponding decrease of approximately one mg/kg in the concentration of Cu in the rice‐plant tissue. Multiple regressions of extractable Cu by eight methods with soil organic matter content accounted for from 53.4 to 70.0% of the variations in the prediction of the concentration of Cu in the rice plants. Combinations of other soil chemical properties measured with extractable Cu did not significantly improve the predictability  相似文献   

9.
Abstract

Tomato plants were grown in sand culture with NH+ 4, and NO? 3, forms of N and three levels of light. Plants supplied with NH+ 4, nutrition under high light intensity had symptoms of stunting, leaf roll, wilting, interveinal chlorosis of the older leaves, and one third the dry weight of N03‐fed plants. In contrast, growth of plants receiving NH+ 4, nutrition under shade appeared normal although dry weight was reduced. NH4‐N nutrition suppressed K, Ca and Mg accumulation in tissues and increased P contents as compared to NO3‐N nutrition.  相似文献   

10.
Sustainable management of nitrogen (N) in crop production requires a multifactorial assessment of the soil inorganic nitrogen pool (Nmin). It is assumed that the reliable prediction of the total Nmin content requires data on the content of mineral N forms (NO3‐N, NH4‐N), the contents of other extractable macronutrients and the soil pH. This hypothesis was tested during three growing seasons on a production farm in Górzno, Poland. The contents of 0.01 M CaCl2‐extractable NO3‐N, NH4‐N, P, K, and Mg and the pH were measured in soil layers of 0–0.3, 0.3–0.6, and 0.6–0.9 m just prior to the start of spring vegetation of a given crop and immediately after its harvest (autumn). This study was conducted in 17 fields differing in cropping sequence (CS): 10 with oilseed rape (Brassica napus L.) (OSR‐CS) and seven with maize (Zea mays L.) (SM‐CS) as the dominant crops. Principal factor analysis (PFA) was applied to explore and interpret patterns in data sets defined by the changeability in the content of Nmin in association with variability in contents of other CaCl2‐extractable nutrients. In spring, the first principal factor (PF1) for OSR‐CS was associated with phosphorus (P), whereas PF2 and PF3 were loaded by NO3‐N and NH4‐N, respectively. For SM‐CS, PF1 was loaded by both inorganic N forms, whereas PF2 and PF3 were loaded by potassium (K), magnesium (Mg), and P. In autumn, the dominance of P as the key variable associated with the PFs was stronger in both CSs compared with those in the spring. The prediction of Nmin, in spite of the moderate strength of the PFs (“r” coefficients), can be conducted based on the inorganic N content. In spring, the reliable prediction of Nmin for the OSR‐CS requires data on both N forms. In the SM‐CS, the content of NO3‐N can be used as the sole Nmin predictor. In autumn, the variability in Nmin content can be explained based solely on the NH4‐N content. This was also the main factor affecting the variability in other soil fertility characteristics, such as the contents of K and Mg and the soil pH.  相似文献   

11.
Abstract

Combinations of NH4‐N:NO3‐N usually result in higher tomato (Lycopersicon esculentum Mill.) yields than when either form of nitrogen (N) was used alone. Leaf chlorophyll content is closely related to leaf N content, but the effect of the NH4‐N:NO3‐N ratio on leaf greenness was not clear. The objective of this study was to determine the influence of NH4‐N:NO3‐N ratios on chlorophyll meter (SPAD) readings, and evaluate the meter as a N status estimator and tomato yield predictor in greenhouse production systems. Fruit yield and SPAD readings increased as the amount of NH4‐N in solution increased up to 25%, while higher ratios of NH4‐N resulted in a decline in both. The N concentration in tomato leaves increased as concentration of NH4‐N in solution increased. Fruit yield increased as chlorophyll readings increased. SPAD readings, total N in leaves, fresh weight of shoots, and fruit yield all showed a quadratic response to NH4‐N, reaching a peak at 25 or 50% of N as NH4‐N. SPAD readings taken at the vegetative and flowering stages of growth had the highest correlation (r2=0.54) with N concentration in leaves, but this could not be used as a reliable estimate of N status and fruit yield. Lack of correspondence between high N concentration values and fruit yield indicated a detrimental effect of NH4‐N on chlorophyll molecules or chloroplast structure. The SPAD readings, however, may be used to determine the optimum NH4‐N concentration in solution to maximize fruit yield.  相似文献   

12.
Abstract

Inhibition of nitrification in soil results in a decreased ratio of nitrate‐nitrogen (NO3‐N) to ammonium‐nitrogen (NH4‐N). If the conditions for NO3‐N loss by leaching or denitrification exist, nitrification inhibitors should increase concentrations of total inorganic soil nitrogen (N) (TISN) (NH4‐N + NO3‐N). This can then result in plants taking up more N and developing more crop yield or biomass. This study examined whether inhibition of nitrification by dicyandiamide (DCD) would result in increased concentrations of TISN under field conditions. The effects of DCD on soil N were evaluated in hyperthermic sandy soils planted to potato (Solanum tuberosum L., cv. Atlantic). Treatments were factorial combinations of N as ammonium nitrate (NH4NO3) at 67, 134, and 202 kg N ha‐1 and DCD at 0, 5.6, and 11.2 kg DCD ha‐1. Soil NH4‐N, NO3‐N, and TISN concentrations were determined for up to five potato growth stages at two locations for two years for a total of 16 determinations (cases), i.e., four were not determined. The N form ratio [NO3‐N/(NH4‐N + NO3‐N] x 100 was decreased in 10 of 16 cases, indicating that nitrification was inhibited by DCD. With two of these 10 cases, TISN concentration increased, but with four others, TISN concentration decreased with at least one N rate. With four of these 10 cases, inhibition of nitrification had no effect on TISN concentration. Under the conditions of these field studies, DCD inhibited nitrification more often than not. Inhibition of nitrification was, however, more likely to reduce TISN concentration than to increase it. This may have been due to DCD effects on immobization of applied NH4‐N.  相似文献   

13.
Abstract

Very low recovery of NH4+‐N was observed in total N determination of (NH4)2SO4 in KC1 solutions by a semimicro Kjeldahl method using permanganate and reduced iron to recover NO3‐ and NO2‐, whereas complete recovery was obtained in analysis of NH4+‐N in water, and of NO3 ?‐N or NO2 ?‐N in either water or KC1 solutions. The loss of NH4 +‐N observed with KC1 was attributed to the formation of NCl3 upon reaction of NH4 + with Cl2 generated during oxidation of Cl? by MnO4 ?. This difficulty is avoided by using K2SO4 instead of KC1 for extraction of inorganic N from soil. Complete recovery was obtained by adding 15N‐labeled NH4+, NO3‐, or NO2‐ to 0.5 M K2SO4 soil extracts, and total 15N analyses of the labeled extracts were in good agreement with values calculated from the additions of 15N and the total N contents of the soil extracts.  相似文献   

14.
Abstract

This study was undertaken to assess the mineralization of nitrogen (N) in rice soils amended with organic residues under flooded condition. A lab incubation study with a 3x3 factorial design (two replications) was conducted with three rice soils (Joydebpur, Faridpur, and Thakurgaon) receiving the following treatments: 1) control, 2) rice straw (Oryza sativa L.), or 3) pea vine (Pisum sativum L.). The organic residue (25 mg straw g‐1 soil) was mixed with soil and glass beads (1:1, soil to beads ratio), and transferred into a Pyrex leaching tube, flooded and then incubated at 35°C for up to 12 weeks. The soils in the leaching tubes were leached (while maintaining flooded condition) at 1,2,4, 8, and 12 weeks with deionized water for determination of NH4‐N, NO3‐N, pH, and Eh. Nitrogen mineralization in soils amended with rice straw was somewhat different than that of soils treated with pea vine. Soil treated with rice straw had a higher N mineralization rate than soils treated with pea vine, which was due to a lower carbon (C):N ratio for rice straw. The potentially mineralizable N pool (No) in soils amended with rice straw and pea vine under flooded conditions, estimated using a 1st order exponential equation, were 7 to 15 times, and 3 to 9 times greater for rice straw No values and pea vine, respectively, than the control. The KN values for unamended soils ranged from 0.35 to 0.52 mg N kg‐1 wk‐1 and rice straw and pea vine treated soils were from 0.75 to 1.22 and 0.46 to 0.58 mgN kg‐1 wk‐1. The lower No and KN values in pea vine treatments suggested there was greater immobilization of N than in rice straw treatments.  相似文献   

15.
Inorganic nitrogen (N) in soils is a primary component of soil‐plant N buffering. This study was conducted to determine if non‐exchangeable ammonium‐nitrogen (NH4‐N) could serve as an index of potentially mineralizable organic N which is an important sink in N buffering. Four long‐term winter wheat (Triticum aestivum L.) experiments that had received annual fertilizer N at 0 to 272 kg N ha‐1 were used. Soils from these experiments were extracted by four 10 mL portions of 2M potassium chloride (KC1) at room temperature followed by extraction with 20 mL of 2M hot KC1. Extraction at 100°C for four hours using 3 g soil and 20 mL 2M KC1 was found to be the most effective. Hot KC1‐extractable NH4‐N minus room temperature KCl‐extractable NH4‐N was considered non‐exchangeable NH4‐N. Non‐exchangeable NH4‐N was correlated with the long‐term N rates, and believed to be a reliable index of potentially mineralizable organic N. The relationship was linear for NH4‐N where the lowest N rate had the lowest extractable N. The mean non‐exchangeable NH4‐N concentration ranged from 8.42 to 16.34 mg kg‐1; whereas, nitrate‐nitrogen (NO3‐N) ranged from 0.07 to 1.87 mg kg1. Total inorganic N extracted was similar to that mineralized in a 42‐day aerobic water saturated incubation. In addition, using a linear‐plateau model, extractable NH4‐N was highly correlated with long‐term average yield (R2=0.92). For the soils evaluated, this method provided a rapid measure of potentially mineralizable N.  相似文献   

16.
Urine patches are significant hot‐spots of C and N transformations. To investigate the effects of urine composition on C and N turnover and gaseous emissions from a Danish pasture soil, a field plot study was carried out in September 2001. Cattle urine was amended with two levels of 13C‐ and 15N‐labeled urea, corresponding to 5.58 and 9.54 g urea‐N l–1, to reflect two levels of protein intake. Urine was then added to a sandy‐loam pasture soil equivalent to a rate of 23.3 or 39.8 g urea‐N m–2. Pools and isotopic labeling of nitrous oxide (N2O) and CO2 emissions, extractable urea, ammonium (NH4+), and nitrate (NO3–), and plant uptake were monitored during a 14 d period, while ammonia (NH3) losses were estimated in separate plots amended with unlabeled urine. Ammonia volatilization was estimated to account for 14% and 12% of the urea‐N applied in the low (UL) and high (UH) urea treatment, respectively. The recovery of urea‐derived N as NH4+ increased during the first several days, but isotopic dilution was significant, possibly as a result of stress‐induced microbial metabolism. After a 2 d lag phase, nitrification proceeded at similar rates in UL and UH despite a significant difference in NH4+ availability. Nitrous oxide fluxes were low, but generally increased during the 14 d period, as did the proportion derived from urea‐N. On day 14, the contribution from urea was 23% (UL) and 13% (UH treatment), respectively. Cumulative total losses of N2O during the 14 d period corresponded to 0.021% (UL) and 0.015% (UH) of applied urea‐N. Nitrification was probably the source of N2O. Emission of urea‐derived C as CO2 was only detectable within the first 24 h. Urea‐derived C and N in above‐ground plant material was only significant at the first sampling, indicating that uptake of urine‐C and N via the leaves was small. Urine composition did not influence the potential for N2O emissions from urine patches under the experimental conditions, but the importance of site conditions and season should be investigated further.  相似文献   

17.
Abstract

Mixtures of cation and anion exchange resins are used as part of the resin core technique to determine nitrogen transformation in forest soils as they adsorb the NH4‐N and NO3‐N from soil solution percolating through the incubated soil cores. In the field, the exchange resins may be subjected to a variety of conditions, involving drying, rehydration, freezing, and thawing. This paper examines how these processes affect adsorption of NH4‐N and NO3‐N and the stability of the resins. Lab tests were performed on the anion resin Amberlite IRA‐93, the cation resin Amberlite IR‐120, a mixture of IRA‐93 and IR‐120, and the commercially‐mixed bed resin Amberlite MB1. The background content of NO3‐N and NH4‐N on the resins was large and highly variable between different batches of resins in spite of a 2 M NaCl pre‐rinse. The IR‐120 cation resin that was subjected to 48 hours air‐drying contained significantly less NH4‐N than the moist resins, while the drying of the IRA‐93 anion resin caused a significant release of NO3‐N from resins with no N addition. Although the variation was large, the mixed bed resin MB1 indicated a release of NH4‐N, which supports results from long term in situ deployments. A reduced adsorption of NO3‐N was found on the IRA‐93 anion resins and the MB1 mixed bed resins that were dried prior to N addition while the dry IR‐120 cation resins adsorbec significantly less NH4‐N than the control resin. No effect of freezing and thawing efficiency was observed on resin stability or N adsorption efficiency. Sufficient blanks that have been subjected to similar moisture changes are necessary in N limited systems with low levels of available NH4‐N and NO3‐N.  相似文献   

18.
Abstract

In a pot experiment, the effects of NO3‐N and NH4‐N fertilizer were examined on the pH of the bulk soil and rhizosphere, and on the growth and nutrient uptake of 18–35‐d old bean plants (Phaseolus vulgaris L.) supplied with KH2PO4 or rock phosphate (Hyperphos). Prior to sowing, the soil was incubated for 16 d to ensure complete nitrification of NH4‐N which decreased bulk soil pH from 6.8 to 5.5. In other pots, a nitrification inhibitor, N‐Serve, was added together with the ammonium fertilizer and after 18 d growth, the pH of the bulk soil was 6.6 while the pH of the rhizosphere decreased to 4.5. Shoot and root dry matter yield was significally greater for plants supplied with KH2PO4 and fertilized with NH4‐N compared with NO3‐N. This increased growth by NH4‐N fed plants was presumably due to a increased nutrient availability caused by the acidification of the bulk soil. Shoot concentrations of ? and micronutrients, such as Fe, Mn, Zn, and Cu, were higher for plants supplied with NH4‐N, and more strikingly were higher for plats supplied with NH4‐N+N‐Serve when expressed on a root length basis. In this latter case, the increased nutrient acquisition by plants could only be due to acidification of the rhizopshere. The inhibitory effect of NH4‐N+N‐Serve, particularly on root growth, was not caused by NH4+ toxicity, but was due to a direct effect of N‐Serve as shown by growth comparisons with another nitrification inhibitor, dicyanodiamide (DCD).  相似文献   

19.
Abstract

To evaluate the chance to reduce leaf NO3 content and to increase capability to use NH4‐N even in the absence of NO3‐N in the nutrient solution, plants of two Apiaceae species, fennel (Foeniculum vulgare Miller var. azoricum Mill. Thell.) and celery (Apium graveolens L. var. dulce Mill. Pers.), and of one species of Chenopodiaceae, Swiss chard (Beta vulgaris L. var. vulgaris), were hydroponically grown in a growth chamber with three different NH4‐N: NO3‐N (NH4: NO3) ratios (100: 0,50: 50, and 0: 100), but with the same total N level (4 mM) for 14 days. Swiss chard growth was inhibited by NH4 nutrition and reached the highest values with the NH4: NO3 ratio 0: 100. For all the morphological and yield features analyzed, fennel and celery resulted to be quite unresponsive to nitrogen (N) chemical form. Water use efficiency increased in Swiss chard and decreased in fennel and celery with the increase of NO3‐N percentage in the nutrient solution. The dependency of N uptake rate on shoot increment per unit root was more conspicuous for Swiss chard than fennel and celery. All species took more NO3‐N than NH4‐N when N was administered in mixed form. In the best conditions of N nutrition, Swiss chard accumulated NO3 in leaves in high concentration (3,809 mg kg"1 fresh mass). On average, fennel and celery accumulated 564 mg NO3 kg?1 fresh mass with the ratio NH4: NO3100: 0 and showed that by using NH4 produce having very low NO3 content can be obtained. By increasing NO3‐N percentage in the nutrient solution; NO3 leaf content of fennel and celery increased remarkably (7,802 mg kg?1 fresh mass with the ratio N H4: NO3 0: 100).  相似文献   

20.
The contribution of bacteria and fungi to NH4+ and organic N (Norg) oxidation was determined in a grassland soil (pH 6.3) by using the general bacterial inhibitor streptomycin or the fungal inhibitor cycloheximide in a laboratory incubation study at 20°C. Each inhibitor was applied at a rate of 3 mg g?1 oven‐dry soil. The size and enrichment of the mineral N pools from differentially (NH415NO3 and 15NH4NO3) and doubly labelled (15NH415NO3) NH4NO3 were measured at 3, 6, 12, 24, 48, 72, 96 and 120 hours after N addition. Labelled N was applied to each treatment, to supply NH4+‐N and NO3?‐N at 3.15 μmol N g?1 oven‐dry soil. The N treatments were enriched to 60 atom % excess in 15N and acetate was added at 100 μmol C g?1 oven‐dry soil, to provide a readily available carbon source. The oxidation rates of NH4+ and Norg were analysed separately for each inhibitor treatment with a 15N tracing model. In the absence of inhibitors, the rates of NH4+ oxidation and organic N oxidation were 0.0045 μmol N g?1 hour?1 and 0.0023 μmol N g?1 hour?1, respectively. Streptomycin had no effect on nitrification but cycloheximide inhibited the oxidation of NH4+ by 89% and the oxidation of organic N by more than 30%. The current study provides evidence to suggest that nitrification in grassland soil is carried out by fungi and that they can simultaneously oxidize NH4+ and organic N.  相似文献   

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