Aluminium contamination and other changes of acid soil solution isolated by means of porcelain suction-cups

Comparison was made between the chemical composition of soil solutions isolated by means of a suction method using porcelain cups and by centrifugation. The soil solutions were isolated from three depths of field plots, where the soil (Typic Haplohumod) had been subjected to various pretreatments.
The cups were made of mullite and corundum as shown by X-ray diffraction analysis. The material when powdered had a cation exchange capacity of about 10meq kg⁻¹. Solutions with similar ionic strengths were obtained by the two methods, but the cups were found to release substantial amounts of Al and to adsorb H, Ca, K, Na and organic matter.
After the cups had been placed in the soil for more than 7 months, calculations suggested that the Al activity in cup solutions was controlled by amorphous gibbsite. This amorphous material was probably produced by proton-induced decomposition of part of the cup material. It is concluded that such cups are improper for isolation of soil solution from acid soils.     

Aluminium contamination of acid soil solution isolated by means of porcelain suction cups: a reply to a paper by Hughes & Reynolds (1990) and an interpretation of aluminium release

Possible aluminium contamination of acid soil solutions isolated by use of porous porcelain suction cups (‘P.80 type’) was reported by Raulund-Rasmussen (1989). The aluminium release was explained by a proton-induced dissolution of cup material. Hughes & Reynolds (1990) suggested that the aluminium release and proton consumption could be explained by an ion-exchange reaction. In an attempt to understand the mechanism and thereby also the usefulness of suction cups, laboratory experiments were carried out to define mineralogical and chemical composition, stability under acid conditions, cation exchange capacity, and reactivity under conditions relevant to the field. The cups consisted of mullite and corundum (65% Al₂O₃) as shown by X-ray diffraction analysis. The cation exchange capacity of the cups was too low (0.65 μmol_c per cup) to explain the observed contamination of isolated soil solution. Ground cup material dissolved slowly in acid. Investigations on whole cups showed that aluminium release to acid test solutions depended on the time of exposure. It is concluded that porcelain suction cups may lead to contamination of isolated soil solution depending on: (i) the intake rate, (ii) the rinsing procedure before sampling, and (iii) the composition of the soil solution (pH and aluminium ion activity being important parameters).     

Novel micro–suction‐cup design for sampling soil solution at defined distances from roots

Micro–suction cups made of nylon membranes and polyacrylic tubes with planar geometry of the membrane were designed for repeated sampling of rhizosphere solution at defined distances from a root monolayer. Adsorption tests revealed that the materials used (nylon membrane, polyacrylic tube) have little influence on the concentration of heavy metals in the sample solution, whereas some organic acids are partly retained by the suction cup. A sampling protocol was developed for collecting extremely small solution volumes (i.e., droplets of 28.3±2.46 μl) for subsequent measurements of trace elements using ICP‐SFMS. A homogeneity test showed that soil‐solution concentrations of Ca, K, Mg, and Ni could be reproduced independent of the suction‐cup position in a rhizobox experiment without plants. In a similar experiment, the rhizobox was planted with the Ni hyperaccumulator Thlaspi goesingense. Compared to more distant soil layers, an increase of Ni and a concurrent decrease of Ca, K, and Mg at 1 mm distance from the root plane was found. These changes can be related to plant uptake and mobilization processes. Our results show that the novel micro–suction cups are a valuable tool for elucidating rhizosphere processes.     

Short Communication — Kurzmitteilung Siliziumcarbid — eine Alternative zur Aluminiumoxid‐Saugkerze?

Siliciumcarbide — is it an alternative to suction cups made of aluminumoxide? Siliziumcarbide (SiC) is a novel non‐oxide ceramic material. We tested differently preconditioned SiC and aluminum‐oxide ceramics (P80) with respect to their influence on the solution passing through. For this we used a cation standard, an anion standard and a soil solution. Both ceramics released considerable amounts of Na and Al. However, in most cases SiC showed better results for anions and dissolved organic carbon. Therefore it may be a promising task to improve the properties of SiC by minimizing sinter additives and optimized conditioning procedures, and develop improved suction cups.     

Adsorption von Pflanzenschutzmitteln und DOC an Saugkerzen aus Glas und Keramik

Sorption of pesticides and DOC on glass and ceramic suction cups Suction cups are widely used for the sampling of soil solution. Due to sorption and desorption processes the concentration of dissolved substances in the samples may vary considerably depending on the material of the suction cups. In order to minimize these losses, a new glass suction cup was developed. In laboratory studies, aqueous solutions of pesticides and DOC were percolated through both types of suction cups; the concentration of pesticides and DOC in the percolates was examined. The pesticides pendimethaline, terbuthylazine, metolachlor and chlortoluron were tested at concentrations of 2, 20, and 200 μg 1⁻¹. The average losses due to sorption by the suction cups were 10% (1.1—31%) for the ceramic cups and 3.1% (0—11%) for the glass cups. Sorption effects increased with increasing hydrophobicity of the pesticides and decreasing pesticide concentrations. Thus, at a concentration of 2 μg 1⁻¹ ceramic cups sorbed 31% of pendimethaline compared with 7.7% in the case of glass cups. Corresponding tests with soilborne DOC solutions yielded comparable results. Ceramic suction cups adsorbed up to 50% of the DOC input concentration, while glass cups retarded 2.4% on average. These results are especially noteworthy because soilborne dissolved organic substances are effective sorbents and carriers for pesticides. The new type of glass suction cups may help to improve the results of pesticide field studies and, in consequence, the assessment and prediction of the leaching behavior of pesticides.     

Mikroskalige Variabilität der Bodenlösungschemie - Ergebnisse eines Laborversuchs zum Vergleich von Standard- und Mikro-Saugkerzen

Microscalic variability of soil solution chemistry - results of a laboratory experiment comparing standard - with micro suction cups In a laboratory experiment with an undisturbed soil column, the chemistry of soil solution collected by a standard suction cup (Ø 2 cm) was compared with that of 20 micro suction cups (Ø I mm) installed in the same soil depth. The standard cup showed comparable concentrations of inorganic anions with the soil column leachate, because preferably the main water paths of the soil column were sampled. In contrast, about 30 % of the micro suction cups sample soil compartments that have a different solution chemistry. In these cases the differences between standard and micro suction cups decrease in the order nitrate, chloride, sulfate. Standard suction cups seem to be the right sampling device for the investigation of element fluxes through soil. To get information about plant availability of ions they are inadequate, due to their dimension. Here micro suction cups are more appropriate, because their dimension is comparable to plant roots.     

Sorption of trace metals by suction cups of aluminium oxide,ceramic and plastics

The sorption properties of ceramic, aluminium oxide and plastic suction cups in respect to trace metals (Be, Cd, Co, Cu, Mn, Ni, Pb, Zn) were compared in laboratory and field experiments. The sorption effect is determined by the level of the cation exchange capacity of the cup material, the pH-value of the soil solution, the content of dissolved organic carbon, the sampling rate and the sampled volume. Sorption was generally negligible only in case of cobalt, manganese and nickel. At low pH-values no retention of trace metals occurred with the exception of lead in the aluminium oxide and the ceramic cups. At pH-values of about 8 cadmium and zinc were strongly sorbed only by aluminium oxide and ceramic cups whereas beryllium, copper and lead were markedly sorbed at this pH-range by all cup types. These results are only valid for the boundary conditions used. Whenever a suction cup's suitability is in doubt it should be tested after a conditioning procedure using realistic boundary conditions.     

Ionic contents of leachate from grassland soils: a comparison between ceramic suction cup samples and drainage

Abstract. Ceramic suction cups were used to obtain samples of soil solution from permanently grazed swards receiving 200 kg N/ha/y. The suction cups were installed in 1 ha plots at 10, 30 and 60 an depth in a poorly drained, heavy clay soil in S. W. England. The plots were hydrologically isolated from each other by perimeter drains which channelled surface runoff water into v-notch weirs. In one treatment, artificial drainage by a system of field and mole drains also converged to outfalls through v-notch weirs, which enabled samples to be taken. Nitrate and a range of other ionic constituents were examined over a 12 month period in soil solutions taken from the suction cups and compared with leachate obtained from the field drains and surface channels. Field drain samples frequently exceeded the EC limit of 11.3 mg nitrate-N/1, but concentrations in suction cups obtained during the same period did not, and were up to ten-fold less. Although correlations for ions were found between different sampling depths and drainage samples, no clear patterns emerged. It was concluded that suction cups were inappropriate for the determination of the overall leaching losses in this soil type, but provided useful data on changes in ionic concentrations which occurred in different soil horizons through to drainage outfalls.     

Sorption of Dissolved Organic Carbon by Ceramic P 80 Suction Cups

Comparison is made between the chemical composition of acid soil solutions percolated through new, acid-washed ceramic P 80 suction cups, and old, over 3 years field-equilibrated suction cups with respect to quantitative and qualitative changes of dissolved organic carbon (DOC). While new suction cups sorb DOC in significant amounts with hydrophobic constituents preferred, field-equilibrated suction cups alter DOC neither in concentration nor in composition. But at changes of DOC concentrations a percolation volume of 300 ml is necessary for reaching equilibrium. It is, therefore, concluded that field-equilibrated ceramic P 80 suction cups can be used for collecting DOC from mineral B and C horizons of acid forest soils, where DOC concentrations remain constant. In contrast, the suction cups investigated are unsuitable for collecting A horizon solutions, which show greater variations in DOC concentration.     

Combination of micro suction cups and time-domain reflectometry to measure osmotic potential gradients between bulk soil and rhizosphere at high resolution in time and space

A prerequisite to investigate the importance of osmotic potential (Ψ_o) in relation to matric potential (Ψ_m) in the soil for water uptake is the existence of a method that measures the temporal and spatial dynamics of Ψ_o in the vicinity of roots. One method for measuring Ψ_oin situ is the collection of soil solution with micro suction cups, the spatial resolution of which is suitable for rhizosphere studies. A major drawback of soil solution sampling is the disturbance of soil solution equilibrium, which makes frequent measurements impossible, so another method is required to provide information on the temporal dynamics of Ψ_o. The time‐domain reflectometry (TDR) technique might be suitable as the signal attenuation (σ) shows a close linear correlation with the salt concentration for a known soil water content. The temporal resolution of the TDR technique is high and the measurement has no impact on soil solution equilibrium. However, the spatial resolution of the TDR technique is too coarse to be used on its own in rhizosphere studies. We used a combination of TDR (fine temporal resolution) and micro suction cups (fine spatial resolution) to measure Ψ_o in a model system with Zea mays grown in quartz substrates. Osmotic potential changed continuously with time, and a steep gradient between bulk soil and the root compartment developed during the 39‐day growing period. The steepest gradient measured over a distance of 6 mm across the nylon net, separating the bulk soil from the root compartment, was ?365 kPa. The combination of both methods made it possible to extend the time interval between micro suction cup samplings and thus minimize the impact of sampling on soil solution equilibrium. Problems of separate calibration were avoided by calibrating the TDR measurements against the results obtained with the micro suction cups within the same experiment.     

Nitrat‐Austräge auf intensiv und extensiv beweidetem Grünland,erfasst mittels Saugkerzen‐ und Nmin‐Beprobung II Variabilität der NO3‐ und NH4‐Werte und Aussagegenauigkeit der Messmethoden

Nitrate leaching from intensively and extensively grazed grassland measured with suction cup samplers and sampling of soil mineral‐N II Variability of NO₃ and NH₄ values and degree of accuracy of the measurement methods Data from a grazing experiment — comparison of mean values, see Anger et al. (2002) — were used to estimate within‐field variability to asses the accuracy of two frequently used methods of estimating NO₃ leaching on pastures: (1) the ceramic suction cup sampling (with 34 cups ha^—1 minimum, calculated climatic water balance, 4 leaching periods) and (2) using the soil mineral‐N method (vertical soil NO₃ and NH₄ content in 0—0.9 m (N_min) measured at the beginning and end of two winters on a minimum of 10 different areas of 50 m² each with a minimum of 7 different sample cores). These methods were used on two permanent pastures with high mean stocking density of cattle of 4.9 LU ha^—1 on 1.3 ha with N‐fertilization of 250 kg N ha^—1 (= intensive [I]) and 2.9 LU without N fertilization on a 2.2 ha pasture (= extensive [E]). The results show that NO₃ leaching on pastures was largely due to few selectively extremely high NO₃ amounts under a few excrement spots — mainly urine spots — which would not be sampled representatively with an acceptable effort in a conventional grazing experiment. In both grazing treatments, very large spatial variation occurred. This was greater between the different suction cups than between the compound mineral N samples of each area. Therefore, a marked skewness and kurtosis demonstrated a non‐normal distribution of samples from suction cups, while mineral N values did not show this effect consistently. Sampling selected mostly spots without noticeable influence of excrement, but a few samples with very high values identified evidently urine spots from summer or autumn grazing. The differences in mean coefficient of variation (CV) between the grazing treatments and estimation methods were mainly based on the stocking rate and the density of excrement spots. CV values were 131 % [I] / 242 % [E] for NO₃ leaching measured with suction cup samplers and of 71 % [I] / 116 % [E] for soil NO₃ values and 24 % [I] / 34 % [E] for soil NH₄ values in 0—0.9 m according N_min‐method. Results of the N_min method are obviously inaccurate even with a sampling intensity much greater than 70 cores ha^—1; and so making an estimation of NO₃ leaching by this method is unsatisfactory for pastures. Compared to this, the results of suction cup sampling are more convincing; but even with a tolerated deviation of ± 20 % from the empirically estimated average and with a 95 %‐confidence interval, the calculated mean minimum number of samples in our experiment should be increased to 146 and 265 suction cups ha^—1 for the intensively and extensively grazed treatments, respectively. This requirement would be prohibitive for many field experiments.     

Measurement of redox potential inside a suction probe

Ceramic suction probes were combined with internal redox electrodes in order to reduce the deviation between site parallels, and to relate redox potential measurements directly to the solution analyzed chemically. In a laboratory experiment soil material was water‐saturated for 49 days and temporal changes of redox potential and pH outside and inside the ceramic suction probes were recorded. Furthermore, iron concentrations inside the ceramic cups were detected. Results indicate that a device combining ceramic suction probes and redox electrodes is in principal possible. However, the device used here could not reduce the deviation between site replications compared to free installed redox electrodes. Increasing iron concentrations due to decreasing redox potentials outside and inside the ceramic suction probes indicate that the soil water iron dynamic is at least partly measurable using this device.<?show $6#>     

Mineralization of Forest Soil Carbon: Interactions with Metals

Biodegradability of natural dissolved organic compounds was tested in laboratory experiments. Organic matter was extracted from organic and mineral forest soil horizons and was isolated from soil solutions collected by suction cups. Carbon moieties were fractionated into hydrophobic acids, hydrophilic acids, and hydrophilic neutral compounds. Degradability of the organic compounds ranged from less than 5% (acid compounds) to 15% (neutral compounds). Metals (Ca, Al) and solid Al₂O₃ were added to assess the effect of complexation reactions as well as the adsorption of organic ligands to mineral surfaces on the rate of mineralization. The rate of CO₂ respiration was used to measure the degradability. Glucose was used as reference compound and we found that the addition of metals retarded its mineralization. On the contrary the degradation of natural soil organic carbon was not affected, or was even enhanced, with Ca or Al added. Adsorption of organic matter to Al₂O₃ decreased the respiration rate by one order of magnitude.     

Improve Water and Nutrient Efficiency in Tomato Crop by a Dynamic Fertigation Management under Saline Conditions

The improvement of water and nutrient efficiency leads to a production model that is more sustainable with less water, fewer fertilizer inputs, and less environmental damages. High-technology fertigation equipment permits high precision in the nutrient solution application. Besides, the field measurement of soil water content by tensiometers and the extraction of soil solutions by suction cups allow a dynamic methodology management in agreement with real crop requirements. This trial was carried out to compare this dynamic fertigation management method (using tensiometers and suction cups) for tomato crops (Lycopersicum sculentum Mill. Forteza) under Mediterranean greenhouse conditions with other methods: the local traditional model, based only on technical consulting, and the classical model, by means of estimation of Kc and nutrient extractions references. The parameters studied were tomato yield, water, and fertilizer amounts applied during the cultivation as well as water- and fertilizer-use efficiency. The water used to prepare the nutrient solution was classified as C₄-S₃ following the Riverside classification system. Plants were grown from 15 August to 20 April. The results show that the supply of fertilizers during the cultivation has been significantly lower with classical and dynamic models. Dynamic method shows greater efficiencies for all the elements, except for potassium, and also decreases the water consumption, not affecting total yield.     

Sickerwassergewinnung mittels Saugkerzen – eine Literaturstudie

Sampling seepage water with suction cups – a literature study The article presents a literature study concerning the sampling of seepage water with suction cups. It gives a general view about construction and materials of different types of suction cups as well as proposals for the installation and arrangement of sampling equipments. Furthermore the article deals with questions related to the release or the sorption of substances by the cup material. Other problems like the influence of the applied suction on the concentration of the solutants in the seepage water sample and the potential field around the suction cup are discussed.     

Einbaubedingte Gefügeänderungen in der Bodenzone um keramische Saugkerzen

Soil fabric changes due to the installation of ceramic suction cups Samples from different sites containing ceramic suction cups with the surrounding soil were taken. After embedding and hardening in polyester resin polished blocks and thin sections were prepared. Soil zones up to 2 cm wide around the cups show up as more or less influenced. Former interaggregate or channel voids disappear. Clay coatings or infillings are smeared over into reoriented streaks. These features appear in dependence upon the predominant grain size distribution. In medium to fine grained soils the said zone is superimposed by a concentric system of fine cracks forming scaly shaped lamellae in perpendicular orientation around the cups. In coarse grained soils the extent of displacement and regrouping of sand grains is hardly visible. Piercing through a banded fabric (B_t-Band), a striking side and downward displacement of grains became obvious. In all cases a flushed silt or fine sand sludge works well to improve the soil/cup contact.     

Bulk sediment bioassays with five species of fresh-water oligochaetes

The fluxes of metals (Na, K, Ca, Mg, Fe, Mn, Al, Cu, Zn, Pb, Cd, Cr, and Ni) in two spruce forest soils in S. Sweden were quantified using the lysimeter technique. Amounts in precipitation (dry and wet), throughfall, litterfall and annual accumulation in biomass were also quantified, as well as stores in soil and biomass. The metal concentrations of the soil solutions varied greatly according to season. The leaching of some metals (Fe, Cu, Pb, Cr, and organic forms of Al) was associated with the leaching of organic matter. These complexes were leached from the A horizon in considerable amounts. They were precipitated in the upper B horizon and only small amounts were transported further downward. By contrast, the leaching of Na, Mg, Ca, Mn, Cd, Zn, Ni, and inorganic forms of Al increased with increasing soil depth. The concentrations of these metals also increased with increasing soil solution acidity. The highest concentrations were often found at the transition to the C horizon. The amounts of Na, K, Mg, Ca, Mn, Al, Zn, Cd, Cr, and Ni leached from the rooting zone were found to be larger than the amounts deposited from the atmosphere, the main source of these metals being the mineral soil. The reverse was true of Ph, Cu, and Fe, the sink being the upper part of the B horizon.     

Verlagerung und Dispersion von Chlorid-, Bromid-, Nitrat- und SulfatTracern in zwei typischen Auenböden

Translocation and dispersion of chloride, bromide, nitrate and sulfate tracers in two typical Fluvi-Eutric Cambisols Chloride, bromide, nitrate and sulfate were applied as tracers on two weakly to moderately acidic Fluvi-Eutric Cambisols. The soil solution was sampled by ceramic suction cups down to a soil depth of 180 cm. At definite time intervals also soils material was taken from different depth to produce the soil saturation extract. The concentrations of the non-adsorbed anions chloride, bromide and nitrate were very similar in the suction cup solutions and in the saturation extracts, whereas the concentrations of the weakly adsorbed sulfate partially showed considerable differences. Obviously both methods extract in acid soils different fractions of the dissolved sulfate. By comparison of marked sulfate peaks with those of chloride, bromide or nitrate, which occur at the same time in different soil depth, a Kd value of 0.16 1/kg can be calculated for the Ap horizon and of 0.02 1/kg for the subsurface horizons of one Fluvi-Eutric Cambisol. Values of the dispersivity of the different horizons were estimated by varying the values of the dispersivity reported in the literature until the best fit of the simulated anion depth distribution to the measured values was found. The estimated dispersivities varied between 1.0 cm in the Ap horizon and 1.8 and 10.0 cm in the subsurface horizons.     

Extraction of water‐soluble organic matter from mineral horizons of forest soils

Dissolved organic matter (DOM) is involved in many important biogeochemical processes in soil. As its collection is laborious, very often water‐soluble organic matter (WSOM) obtained by extracting organic or mineral soil horizons with a dilute salt solution has been used as a substitute of DOM. We extracted WSOM (measured as water‐soluble organic C, WSOC) from seven mineral horizons of three forest soils from North‐Rhine Westphalia, Germany, with demineralized H₂O, 0.01 M CaCl₂, and 0.5 M K₂SO₄. We investigated the quantitative and qualitative effects of the extractants on WSOM and compared it with DOM collected with ceramic suction cups from the same horizons. The amounts of WSOC extracted differed significantly between both the extractants and the horizons. With two exceptions, K₂SO₄ extracted the largest amounts of WSOC (up to 126 mg C kg^–1) followed by H₂O followed by CaCl₂. The H₂O extracts revealed by far the highest molar UV absorptivities at 254 nm (up to 5834 L mol^–1 cm^–1) compared to the salt solutions which is attributed to solubilization of highly aromatic compounds. The amounts of WSOC extracted did not depend on the amounts of Fe and Al oxides as well as on soil organic C and pH. Water‐soluble organic matter extracted by K₂SO₄ bore the largest similarity to DOM due to relatively analogue molar absorptivities. Therefore, we recommend to use this extractant when trying to obtain a substitute for DOM, but as WSOM extraction is a rate‐limited process, the suitability of extraction procedures to obtain a surrogate of DOM remains ambiguous.     

Effects of extraction period and soil.‐solution ratio on the amount of zinc extracted from soils by different extractants

Abstract

Investigations have examined the effects of extraction period and soil:solution ratio on the extraction of zinc from some New Zealand soils by EDTA, DTPA, HCl, Ca(NO₃)₂ and CH₃COONH₄. A high proportion of the zinc extracted by EDTA, DTPA, HCl, and Ca(NO₃)₂ was extracted rapidly, within the first 0.5 h, followed by small increases over the next 15 h. An exception occurred with a soil containing iron/manganese concretionary material. In this soil, with both EDTA and DTPA, there were significant increases in the amount of zinc extracted between 1 and 8 h. The amounts of zinc extracted by CH₃COONH₄ increased gradually with the time of extraction up to approximately 4 h.

Substantial increases in the amounts of zinc extracted with HCl, Ca(NO₃)₂ and CH₃COONH₄ were obtained by increasing the soil:solution ratio from 1:2.5 to 1:10. However, soil:solution ratio has little effect on the amounts of zinc extracted by EDTA or DTPA.