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1.
常规方法准确测定土壤有效钾素变化可能性的探讨   总被引：1，自引：0，他引：1  
土壤中的有效钾状况通常用1 mol L-1中性醋酸铵提取的速效钾或1 mol L-1硝酸煮沸法提取的缓效钾量来表征。我国农田土壤中近些年来1 mol L-1中性醋酸铵提取的速效钾量呈普遍下降趋势。但土壤中的有效钾素的实际下降值,到目前为止还没有办法通过测土的方法进行准确评估。本文通过室内培养实验,人为改变土壤有效钾量,对常规土壤有效钾测定方法反应土壤有效钾素变化的效果进行了比较和评价。并对硝酸连续提取法准确测定土壤钾素变化的可能性进行了探讨。结果表明,几种提取方式中,以2 mol L-1冷硝酸超声波连续提取10次获得的外源钾变化的回收率最高,达75%~80%。其次是1 mol L-1硝酸100℃水浴法连续提取6次,测钾变化的累计回收率可达75%。如进一步增加提取次数,可能会有限地提高测钾变化的回收率,但随提取次数的增加,提取过程的可操作性和结果的稳定性将显著下降。因而用硝酸作为提取剂,即使是在高温、超声波等方式下,也很难准确测定强固钾能力土壤中有效钾的变化。能够准确测定土壤有效钾素变化的方法必须能将土壤中易发生变化的有效态钾全部提出,并尽量不提取土壤的原生矿物态钾,寻找这一方法将是未来土壤钾素测定工作中值得关注的问题。  相似文献   

2.
Three methods of DNA extraction from feed products and four detection methods for the 5'-junction fragment of genetically modified (GM) Roundup Ready soybean (RRS) were compared and evaluated. The DNA extraction methods, including cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and guanidine hydrochloride (Kit), were assessed for their yields and purity of DNA, extraction time, and reagent cost. The DNA yields of CTAB, SDS, and Kit were 52-694, 164-1750 and 23-105 ng/mg sample, and their extraction time was 2.5-3, 2-2.5, and 1.5-2 h with reagent cost about US dollar 0.24, 0.13, and 1.9 per extraction, respectively. The SDS method was generally well suited to all kinds of feed matrices tested. The limits of detection for the four amplification protocols, including loop-mediated isothermal amplification (LAMP), hyperbranched rolling circle amplification (HRCA), conventional polymerase chain reaction (PCR), and real-time PCR, were 48.5, 4.85, 485, and 9 copies of the pTLH10 plasmid, respectively. The ranked results of the four detection methods were based on multiattribute utility theory as follows (from best to worse): HRCA, LAMP, PCR, and real-time PCR. This comparative evaluation was specifically useful for selection of a highly efficient DNA extraction or amplification method for detecting different GM ingredients.  相似文献   

3.
Abstract

Because imazethapyr residues in soils may cause plant injury to certain rotational crops, sensitive, and reliable methods for imazethapyr monitoring in soils are needed. In this study, imazethapyr analysis was investigated using two newly developed procedures: an anion exchange membrane extraction followed by an HPLC‐UV detection and a canola bioassay. Nine soils in which no previous application of imazethapyr had been made were collected from farm fields in Saskatchewan, Canada. Soils were spiked to yield imazethapyr concentrations in the range of 0–80 μg kg‐1 dry soil and were subjected to analysis by the above procedures. In the anion exchange membrane extraction, spiked soils were shaken with the membrane strips; imazethapyr was then eluted from the membranes with a potassium chloride (KC1) solution, partitioned into dichloromethane and injected into the HPLC. This method allowed for the extraction of the ionized portion of imazethapyr from soils. In a laboratory bioassay, pre‐germinated canola seeds were planted in spiked soils and after five days of growth root and shoot growth inhibition was determined. The results of both methods were dependent on soil type. Generally, soils from depressions in the landscape yielded low imazethapyr recovery by anion exchange membrane extraction; these soils also showed low degree of imazethapyr phytotoxicity to canola growth. After imazethapyr field spraying, soils were sampled from the field at different time intervals for up to one year and analyzed in the laboratory by the above methods; also, after one year, a field bioassay was performed. Using the membrane extraction method, imazethapyr was detected only in field samples collected one week after spraying. The membrane extraction method, although very simple and cost‐efficient lacks sensitivity needed for the imazethapyr monitoring at low concentrations in agricultural soils. The 5‐day canola bioassay (root growth inhibition method) was more sensitive than the membrane extraction and showed imazethapyr presence in all field samples. However, because crop growth inhibition was more severe in the field than in the laboratory, a field bioassay may be the most reliable means to assess injury potential for certain sensitive rotational crops under field conditions.  相似文献   

4.
Dissolved organic matter(DOM) in soil plays an important role in the fate and transport of contaminants.It is typically composed of many compounds,but the effect of different extraction factors on the abundance of different DOM components is unknown.In this study,DOM was extracted from three soils(paddy field,vegetable field and forest soils) with various extraction time,liquid to solid ratios(LSRs),extractant types,and extractant concentrations.The LSR had a significant effect on DOM content,which increased by 0.5–4.0 times among the three soils when LSR increased from 2:1 to 10:1(P 0.05).Dissolved organic matter content increased by 4%–53% when extraction time increased from 10 to 300 min(P 0.05).Extractant concentration had different effects on DOM content depending on the extractant.Higher concentrations of KCl promoted DOM extraction,while higher concentrations of KH_2PO_4 inhibited DOM extraction.Therefore,grey relational analysis was used to further quantitatively evaluate the effect of extraction time,LSR,and extractant concentration on DOM,using KCl as an extractant.For the paddy field and forest soils,the impact of these three factors on DOM extraction efficiency was in the following order:KCl concentration LSR extraction time.However,the effect was different for the vegetable field soil:LSR extraction time KCl concentration.Taking all these factors into account,1.50 mol L~(-1) KCl and an LSR of 10:1 with a shaking time of 300 min was recommended as the most appropriate method for soil DOM extraction.  相似文献   

5.
不同浸提剂以及保存方法对土壤矿质氮测定的影响   总被引：4，自引：0，他引：4  
为探明影响土壤矿质氮测定的因素,从棕壤、潮土和黄棕壤3种类型土壤中各采集10个经不同施肥处理的土样,用连续流动注射分析仪测定经不同浸提剂以及不同保存方法处理后土样的NO3-N和NH4-N含量。结果表明:不论是棕壤、潮土还是黄棕壤,2 mol.L?1 KCl提取硝态氮的数量与0.01 mol.L?1 CaCl2提取的数量相关性均达到P<0.01水平;3种土壤各个土样硝态氮含量的测定值多表现为新鲜土<冷冻土<风干土;将鲜样浸提后作短时间的冷冻处理,其效果与鲜样24 h内的测定结果较接近;土样不同保存方式以及浸提液的保存时间对3种土壤NH4-N测定结果的影响规律不及NO3-N明显。  相似文献   

6.
Abstract

Pressurized hot water and DTPA‐Sorbitol are two relatively new, proposed alternative soil boron (B) extraction methods for which no data on yield or plant nutrient uptake have been reported for validation. Both methods initially have shown significant correlation with the hot water extraction method in untreated soils as well as soils incubated with various levels of B. The objective of the research was to extract samples of B‐treated soils by using all three extraction methods and correlate the B values obtained to yield, B tissue concentration, and total B removal of alfalfa (Medicago sativa). Greenhouse and field experiments on alkaline and limed acid soils naturally low in hot water‐extractable B were conducted to test alfalfa response to B fertilizer. In the greenhouse, highly significant relationships exist between plant uptake and extractable B with all three methods at varying levels of applied B, but no alfalfa yield response was observed. All three methods result in accurate predictions of plant B tissue concentrations and total B removal. The field experiment exhibited a significant positive relationship between total alfalfa yield and extractable B using hot water and pressurized hot water extractions. Extractable B using DTPA‐Sorbitol was not related to total alfalfa yield in the field experiment. This work, coupled with the earlier incubation studies, supports the pressurized hot water extraction method as an improvement over hot water in diverse soil types. The lack of relationship in the acid soil supports DTPA‐Sorbitol as an improvement over hot water in alkaline soils.  相似文献   

7.
The cation–anion exchange resin membrane (CAERM) system is one of the most promising alternative methodologies for the assessment of soil phosphorus (P) availability. Nevertheless, the CAERM method has a recommended period of extraction (16 h) that limits its applicability. With the aim to improve the use of CAERM in routine laboratory work, seven extraction times were studied and compared for repeatability and biological accuracy, using 150 samples of soils and covering a wide range of properties. The results showed dissimilar quantities of extractable P, according to the nature of soils and the period of extraction time. On average of all soils, values of extractable P ranged from a 2.4 mg kg?1 and 26.7 mg kg?1 in 0.25‐h and 16‐h extraction times, respectively. Relative to the repeatability aspects, the results reveal a tendency of increasing results with the decrease of the period of extraction, showing coefficient variation (CV) values ranging from 5% (16 h) to 14% (0.25 h). All the extraction periods tested for the CAERM presented highly significant values of r (0.824–0.943) between extractable P and each of the three biological parameters: relative yield of ryegrass, P content, and P uptake. Considering the three biological parameters simultaneously, the best results were obtained for extraction periods of 8 h, 2 h, and 4 h. Based on the results, and considering both practical and accuracy aspects, it is conclude that 2 h of extraction is a valid alternative to the 16‐h standard extraction period for the CAERM methodology.  相似文献   

8.
A robust multi-residue procedure is needed for the analysis of the pro-herbicide isoxaflutole and its degradates in soil and plant materials at environmentally relevant (<1 microg kg-1) levels. An analytical method using turbo-spray and heat-nebulizer high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was developed for the analysis of isoxaflutole (IXF) and its two metabolites, diketonitrile (DKN) and the benzoic acid metabolite (BA), at sub-microgram per kilogram levels in soil and plant samples. The average recoveries of the three compounds in spiked soil and plant samples ranged from 84 to 110% and 94 to 105%, respectively. The limits of quantification were validated at 0.06 microg kg-1 for soil and 0.3 microg kg-1 for plant samples. The limits of detection (LOD) for soil analysis were 0.01, 0.002, and 0.01 microg kg-1 for IXF, DKN, and BA, respectively. Corresponding LOD for the plant analysis method were 0.05, 0.01, and 0.05 microg kg-1. The developed method was validated using forage grass and soil samples collected from a field lysimeter study in which IXF was applied to each of four forage treatments. Forage plants and soils were sampled for analyses 25 days after IXF application to the soil. In soils, IXF was not detected in any treatment, and DKN was the predominant metabolite found. In forage plants, the concentrations of DKN and BA were 10-100-fold higher than that in soil samples, but IXF was not detected in any forage plants. The much higher proportion of BA to DKN in plant tissues (23-53%), as compared to soils (0-5%), suggested that these forages were capable of detoxifying DKN. The developed methods provided LODs at sub-microgram per kilogram levels to determine the fate of IXF and its metabolites in soils and forage plants, and they also represent considerable improvements in extraction recovery rates and detection sensitivity as compared to previous analytical methods for these compounds.  相似文献   

9.
Soil-solid phase associations of Se in seleniferous soils of Punjab were investigated by following sequential extraction procedures involving multiple extractions with 0.2 M K2SO4 (2 times), 0.1 M Na2SeO3 (4 times), 0.05 M NH4OH (4 times), 6 M HCl (2 times) and 9 M HNO3 (2 times) vis-a-vis single extractions with 0.25 M KCl, 0.1 M KH2PO4, 4 M HCl and concentrated HCl. Soil samples were equilibrated with 75Se (as Na2SSeO3) @ 9.25 kBq g - 1 soil by incubating at field capacity moisture regime and subjecting to alternate wetting and drying cycles. Following multiple extraction procedure, out of total 75Se added, 8.8 - 26.1% was present in readily available form (0.2 M K2SO4 extractable); 27.6 - 49.0% as isotopically exchangeable (0.1M Na2SeO3 extractable) and 5.3 - 12.0% as organic Se (0.05 M NH4OH extractable). Selenium extractable in K2SO4 was significantly correlated with free iron (r = - 0.774, p < 0.05) and CaCO3 (r = 0.670, p <0.10) content of the soils. Negative relationship was observed between Se uptake by maize (Zea mays L.) and ammonium hydroxide extractable (r = - 0.752, p <0.05) as well as residual Se (r = - 0.726, p <0.05) in soils. Highly positive coefficients of correlation between isotopically exchangeable Se and Se content (r = 0.851, p <0.01) as well as its uptake by maize (r = 0.841, p <0.01) indicated that the isotopically exchangeable form of Se may be considered as an index of bioavailable Se in seleniferous soils of Punjab. None of the fractions defined by following single extraction procedure was correlated with either the soil characteristics or Se uptake by maize plants. Multiple extraction procedure could, thus, better explain the distribution of Se in different fractions and uptake by plants.  相似文献   

10.
With the electro–ultrafiltration (EUF) technique, the plant availability of several plant nutrients in soils can be characterized. The basic principle of EUF is that an electric field is induced using platinum electrodes. Ions in the soil suspension move either to the cathode or to the anode and are filtrated through ultra‐membrane filters. In the standard EUF procedure, two extractions steps are used: 30 min at 20°C and 5 min at 80°C. However, the determination of micronutrients and heavy metals with the standard EUF procedure is not possible, because the solubility of these elements in water is low and most of the watersoluble elements are precipitated when passing the platinum electrodes. The addition of DTPA, a well known complexing agent, during a third EUF fraction (5 min at 80°C) enables extraction of micronutrients and heavy metals. Highest concentrations in the 33 soils of the study were found for iron, followed by zinc, manganese, lead, copper, and nickel. Lower concentrations were obtained for cobalt, chromium, cadmium, and molybdenum. For two soils, the EUF/DTPA procedure was compared to CaCl2/DTPA and EDTA soil extraction methods, showing that higher or comparable amounts were found with CaCl2/DTPA and much higher amounts with the EDTA method. These results reveal that the EUF/DTPA technique in principle can be used for the determination of plant‐available micronutrients and heavy metals. However, in a next step the relationship between EUF/DTPA‐extractable elements and their availability for plants needs to be quantified.  相似文献   

11.
The objective of this work was to develop protocols to selectively extract prokaryotic DNA from soils, representative of the whole community, amenable to high-throughput whole genome shotgun sequencing. Prokaryotic cells were extracted from soils by blending, followed by gradient centrifugation. Detergent (sodium deoxycholate) was required for complete dispersion of soil aggregates and detachment of prokaryotic cells from a broad range of soil types. Repeated extractions of a given soil sample were critical to maximize cell yield. Furthermore, cells obtained through repeated extractions captured unique prokaryotic assemblages that would otherwise have been missed in single-pass extractions. DNA was isolated from extracted cells using one of the following treatments: i) lysozyme-SDS-proteinase K (enzymatic) digestion; ii) potassium ethyl xanthogenate digestion; or iii) enzymatic digestion of cells embedded in agarose plugs. In addition, these methods were compared to a commercial bead-beating extraction kit (MoBio UltraClean). Of the indirect DNA extraction methods, plug digestion generated the largest yields (up to 70% of yields obtained by direct DNA extraction) of high-molecular weight DNA (>400 kb). Thus, plug digestion is amenable to large-insert metagenomic library construction and analysis. Comparisons of banding patterns generated by RAPD-PCR and DGGE indicated that sequence composition and inferred community composition of a given extract varied greatly with DNA isolation method. While overall diversity did not change significantly with the cell lysis method, analysis of 16S rRNA gene clone libraries revealed that each extraction procedure produced unique distributions of prokaryotic phyla within the sample population.  相似文献   

12.
In the present study, a laboratory experiment was designed to compare the 0.01 M calcium chloride (CaCl2) and diethylenetriaminepentaacetic acid (DTPA) extraction methods for their ability to predict cadmium (Cd), copper (Cu), iron (Fe), Manganese (Mn), nickel (Ni), and zinc (Zn) availability and mobility in five calcareous soils. The soils were spiked with different amounts of metals (0, 50, 100, 200, and 400 mg kg?1) both in binary (Cu and Zn; Ni and Cd; Fe and Mn) and in multi-systems (Cd, Cu, Fe, Mn, Ni, and Zn) and incubated for 1 months at field capacity. In metal-spiked soils, both extraction methods showed a linear relationship of extractable to total metals for all soils. The fraction of total metals extracted by DTPA was much higher than the fraction extracted by CaCl2, which was attributed to the formation of soluble metal-complexes in the complexing extracts calculated by the Visual Minteq program. DTPA extraction method showed higher selectivity for Cu over other metals both in binary and in multi-systems. Different order of metals extractability was found in binary and multi-systems for both extraction methods. Solid/solution distribution coefficient (Kd) was calculated by the ratio of the solid phase to soil solution concentration of metals extracted by CaCl2 or DTPA extraction methods. Both in binary and in multi-systems, the average Kd (l kg?1) of metals by soils were in the order of Mn (5398) > Fe (4413) > Zn (3376) > Cu (2520) > Ni (969) > Cd (350) in the CaCl2-extractable metals and Fe (35) ≥ Ni (34) > Zn (18) > Mn (11.2) > Cu (6.3) > Cd (4) in the DTPA-extractable metals. Results showed that among the six studied metals, Cd had the lowest Kd, implying a relative higher mobility in these calcareous soils. The Visual Minteq indicated that in the CaCl2-extraction method and in both binary and multi-systems the dominant species for Cu, Mn, Ni, and Zn were Cu2+, Mn2+, Ni2+ and Zn2+, respectively, while for Cd and Fe, the dominant species were CdCl+ and Fe(OH)2+, respectively.  相似文献   

13.
The objective was to evaluate alternatives to the peroxide value method of choice in the dairy industry, the method issued by the International Dairy Federation. Furthermore, the study evaluated the feasibility of alternative solvents for extracting lipids and subsequent peroxide value determinations. Packaged cheeses were stored under illuminated display at 4 degrees C to obtain samples with various peroxide contents but with uniform gross composition. The hydroperoxide contents were measured during 3 weeks of storage by applying two lipid extraction methods, Folch and Bureau of Dairy Industry (BDI) extractions, and three different hydroperoxide extraction solutions [chloroform/methanol (7:3, v/v), hexane/2-propanol/methanol (5:7:2, v/v/v), and methanol/decanol/hexane (3:2:1, v/v/v)], prior to standard colorimetric measurements. Extraction yields of fat from Havarti cheeses using the Folch and BDI extraction methods were approximately 109 and 61%, respectively, of the yields obtained by the International Dairy Federation gravimetric reference method. Although differences in fat extraction yields were compensated for, significantly higher peroxide values resulted from the Folch extraction method than from the BDI extraction method. The peroxide values obtained by the three methods were all in the same range, and pronounced linear correlations between peroxide contents determined using the three solutions were noted (r (2) in the range of 0.951-0.983). Peroxide value levels were not significantly different in samples stored in the dark or exposed to light.  相似文献   

14.
The Mehlich 1 (M1) soil-test method has been used for soil phosphorus (P) extraction in southern Brazil. The objective of this work was to compare M1, Mehlich 3 (M3), and ionic exchange resin (resin) soil-test methods to evaluate the soil P available for crops and grasses in soils amended with phosphate rock (PR). Oxisol and Alfisol received triple superphosphate (TS) and PR. The M1 solution extracted greater P amounts in soils amended with PR compared with the M3 solution and resin methods. Lesser P amounts were extracted with the M3 solution. Crops yields were better associated with the P amounts extracted with M3 and resin methods in soils amended with PR. The results showed that M1 overestimates soil P availability to plants in soils amended with PR; the M3 solution best estimated the soil P available for crops and grasses in soils amended with PR.  相似文献   

15.
A headspace solid-phase microextraction (SPME) method was developed for the determination of secondary compounds from Brazilian sugar cane spirits, or cacha?a, by GC-FID. An SPME holder with an 85 microm polyacrylate coating was utilized. The novel method is compared with an optimized method: liquid-liquid extraction (LLE). Both methods showed good linearity, but the repeatability for analyses done with the SPME technique (%RSD = 1.8-3.9) was better than for those done with LLE (%RSD = 10.3-11.7). The concentrations of the analytes obtained in the analysis of 12 cacha?a samples with the SPME technique were higher than those obtained with LLE. In the SPME method the extraction wastes are smaller. Cacha?a samples were qualitatively analyzed for GC-MS.  相似文献   

16.

Background

In practical farming, there is often a need for short-term availability of information on the soil nutrient status.

Aims

To develop a new express method for the extraction of major plant-available nutrients and measurement of soil nutrients. In future, this method shall serve for in-field measurements of soil samples with an ion-sensitive field-effect transistor (ISFET).

Methods

Various extraction conditions such as type of extractant, soil-to-solution ratio, time, and intensity were investigated on a broad selection of dried soil samples in the laboratory. Based on 83 field-moist soil samples with varying clay contents, these conditions were compared to standard laboratory methods.

Results

With increasing extraction time, the nutrient concentrations increased. When the soil-to-solution ratio was reduced, a greater share of nutrients was extracted, independent of soil type. H2O and 0.01 M CaCl2 and standard calcium-acetate-lactate (CAL) solution proved to be too weak in the short period to reach the ISFET sensor measurement range. Higher concentrated CAL solutions performed much better. Finally, a 5-min CaCl2 extraction followed by the removal of an aliquot for the determination of soil pH and NO3− was found to be effective. The remaining solution was then mixed with 0.20 M CAL solution for the analysis of H2PO4− and K+ at 10 min of extra extraction time. This extraction method showed very good correlations with the values based on the German laboratory reference methods for pH (R2 = 0.91) and for nitrate (R2 = 0.95). For phosphorus and potassium, we obtained an R2 of 0.70 and 0.81, respectively, for all soils. When soils were grouped according to clay content higher correlations were found.

Conclusions

A new express method based on a wet-chemical approach with a soil preparation procedure was successfully developed and validated. This seems to be a valuable basis for future in-field measurements via ISFET.  相似文献   

17.
Potassium (K) fertilization of cotton (Gossypium hirsutum L.) has been a major research focus the last few years throughout the cotton belt. The objective of this field research, conducted from 1991 through 1994 on two high Mehlich I extractable K (EK) soils, was to evaluate broadcast and foliar applied K for conventional‐ (CT) and no‐tillage (NT) production. Main plot broadcast K rates were 0, 28, 56, and 112 kg K ha‐1. Foliar sub‐plot treatments were a non‐foliar check, KNO3, and Ca(NO3)2. The KNO3 was applied four times per year at 4.1 kg K ha‐1 application‐1. Calcium nitrate was applied at 1.6 kg N ha‐1 to equal the N applied in the KNO3. Extractable K increased annually with broadcast K for both tillage systems and soils and was higher for NT than CT. Lint yields from CT of both soils were increased two of the eight site‐years while yields from NT were increased five of eight site‐years by broadcast K. Three of the NT site‐year yields plus four‐year mean yields of both soils were increased by applying 56 kg K ha‐1, a rate higher than currently recommended for high EK soils. Yield responses to foliar fertilization were from added N rather than the K. Petiole K levels were sufficient so that extra K applied foliarly was not recommended for either soil or tillage system.  相似文献   

18.
Pressurized fluid extraction (PFE) is a new sample extraction method operated at elevated temperatures and pressures with liquid solvents. The use of PFE was investigated for the extraction of four Hawaiian clayey soils fortified with the selected chloroacetanilide and nitrogen heterocyclic herbicides Alachlor, Bromacil, Hexazinone, Metribuzin, and Tebuthiuron. The effects of operation temperature, pressure, flush volume, and static cycles on PFE performance were studied. Water was the most effective modifier of PFE for quantitative recoveries of the five herbicides in soils. The simple extraction method required pretreatment of the soil with 37.6% water and subsequent two-static-cycle extraction with a total of 32 mL of acetone at 1500 psi and 100 degrees C. Average recoveries of Alachlor, Bromacil, Hexazinone, Metribuzin, and Tebuthiuron ranged from 93 to 103% by the water-assisted PFE, compared with only 68-83% recoveries of the corresponding chemicals when no water was used. The extraction time and total organic solvent consumption were reduced from 18 h and 300 mL by Soxhlet to 22 min or less and 80 mL or less of organic solvent by PFE.  相似文献   

19.
Since Mycobacterium chlorophenolicum strain PCP-1 is not detectable in soil by selective plating, a specific tracking method was based on the polymerase chain reaction (PCR) using soil DNA as a target. A direct extraction protocol based on bead beating was adapted and used to obtain PCR-amplifiable DNA from five different soils. In one soil, the disruption of cells of PCP-1, of Pseudomonas fluorescens R2f and of Paenibacillus azotofixans P3L5, as well as of the indigenous bacteria increased with increasing bead beating times. After 4.5 min, lysis efficiency was about 90% or more in all cases. Total DNA yields varied between soils, from 2 to 35 μg g–1. The purification steps needed to obtain amplifiable DNA were different per soil. To detect target DNA specifically in bacterial cells, a new indirect extraction protocol was developed, which efficiently dislodged bacterial cells from the soil matrix, and produced amplifiable DNA with high yield. To detect strain PCP-1 in soil, 16S ribosomal gene-based PCR combined with oligonucleotide hybridization was applied using a most-probable-number (MPN) set-up, whereas immunofluorescence was used for calibration. Strain PCP-1 was detected shortly after introduction into three soils at about the inoculum levels, as evidenced by both approaches. Both the direct and indirect DNA extraction methods yielded similar MPN estimates. The dynamics of M. chlorophenolicum PCP-1 was estimated in two soils over 14 days via MPN-PCR/oligonucleotide probing. PCP-1 showed good survival in both soils, and results obtained by MPN-PCR with directly and indirectly extracted DNA were internally consistent. Immunofluorescence cell enumerations supported the gross stability of PCP-1 in these two as well as in two additional soils. Received: 8 February 1996  相似文献   

20.

Purpose

Information about phosphorus (P) losses from agricultural catchments in Mediterranean environments is scarce. In this work, P losses in overland flow from two representative small Mediterranean catchments, one dominated by Alfisols and the other by Vertisols, were studied.

Materials and methods

At the lowest level of each catchment, overland flow was measured and several runoff samples taken in each runoff event during two growing seasons (2001–2002 and 2002–2003). After centrifugation, total P in sediments and total and molybdate reactive P in supernatant were determined. Different chemical extraction methods were used to quantify the forms of P in soils and sediments.

Results and discussion

Total P losses in the studied catchments ranged between 0.5 and 3.2 kg ha?1 year?1, losses higher than 2 kg P ha?1 being observed in one event. Phosphorus was mainly lost in the sediments, the ratio of total dissolved P to particulate P being higher in the Alfisol than in the Vertisol catchment. Phosphorus concentration in sediments from the Vertisol catchment was similar to that in the source soils, whereas sediments in the Alfisol catchment had 2.1 times more inorganic P and 9 times more organic P (OP) than the source soils. In the latter catchment, there was an enrichment in the more labile inorganic P forms in the sediments relative to the source soils, which corresponds to a relative enrichment in iron (Fe) oxides by a factor of 2.4. Alfisols had lower TP contents and exhibited lower erosion rates than Vertisols in the studied period but they posed a greater environmental risk than the latter soils because their sediments were richer in P and had a higher proportion of P in forms bound to the Fe oxides compared to the source soils—these P forms can be easily released with the onset of reducing conditions at the bottom of waterbodies.

Conclusions

A study of the P enrichment ratios and the dominant P forms in eroded sediments is therefore necessary to predict the impact of P losses from soils on the ecological quality of waterbodies.  相似文献   

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