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.     

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.     

Die Beeinflussung der Bodenlösung durch Saugkerzen aus Ni-Sintermetall und Keramik

Influencing soil solution by suction cup material (Ni, ceramics) The influence of suction cup material (ceramics, Ni) on the chemical composition of the soil solution was tested in the laboratory by percolating soil solutions of different concentration (pH ～ 4.0). Ceramic cups of P 80 material can be used for the collection of soil solution and its determination for the concentrations of H, Na, K, NH₄, Ca, Mg, Mn, Al, S, Cl and NO₃. They can't be used to determine P-concentrations. The cups must be prepared and preconditioned by leaching large amounts of equilibrium soil solution which should not be oversaturated with respect to the solubility product of AlOHSO₄. The changes in the concentration of extracted soil solution when it passes through the cups depend upon the extracted volume. The lower the volume, the greater are the changes. Sintered Ni-cups show many severe disadvantages (decreasing permeability, insufficient resistence against acid solutions, large variability among single cups), and can only be used for cases where Na, Ca, K, and S are to be determined. Ceramic cups of the type ‘Czeratzki’ are comparable with those of P 80. However, they can only be used, when the concentrations don't vary too much and large amounts of water can be extracted.     

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.     

Evaluation of porous ceramic cups for monitoring soil-water aluminium in acid soils: comment on a paper by Raulund-Rasmussen (1989)

Following recent observations by Raulund-Rasmussen (1989) implicating A1 contamination of soil solutions isolated by suction-cup samplers, A1 release from porous ceramic cups in acid solutions was investigated. In our studies a flush of Al, followed by a gradual decrease in leaching over successive extractions was observed. The amount of Al released was retarded by the presence of 37 μmol dm^?3 of A1 in solution. Gibbsite solubility controls were not observed; all solutions isolated by the cups were undersaturated with respect to amorphous gibbsite. The cups evaluated in this study are appropriate for sampling acidic soil solution, provided they are suitably pretreated and then equilibrated in the field before use.     

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.     

Micro-scale variation of solid-phase properties and soil solution chemistry in a forest podzol and its relation to soil horizons

In order to evaluate micro-scale heterogeneities 55 micro suction cups were placed in an array at 15 mm intervals in a profile face of a cambic podzol. The chemistry of soil solution (mineral anions, pH, UV absorption as a measure for DOC) was compared with solid-phase properties from soil samples (2 cm³ volume), which had surrounded the suction cups. Sequential extraction techniques (water, NF₄Cl, hydroxylamin-hydrochloride, citrate-bicarbonate, oxalate, dithionite-citrate-bicarbonate) and base titrations were applied to characterize the solid phase. Although the average soil solution concentrations between horizons often differed significantly, the spatial distributions of pH and SO₄^2? did not correlate with soil horizon borders. Even if concentration isolines and soil horizon borders were parallel, marked concentration gradients could be observed within individual soil horizons. The less intense the interaction between solute ion and soil matrix, the greater was the variation in solution concentration within a soil horizon. For the soil solid phase only a weak correlation of slow buffer reactions to soil horizons was found. The distribution of extractable Fe and Al was typical for a podzol profile, however, with very steep gradients within single soil horizons. Except for pH, which was related mainly to citrate-bicarbonate extractable aluminium, no solid-phase characteristic showed a clear correlation with soil solution chemistry.     

Effects of organic and inorganic calcium compounds on soil-solution pH and aluminium concentration

The reactions of two organic (citrate and fulvate) and two inorganic (chloride and phosphogypsum) calcium compounds were studied during leaching of columns of unsaturated acidic soil. The potential of these compounds to decrease the aluminium concentration in the soil solution and remove exchangeable aluminium, and their effects on soil acidity are described. The calcium citrate solution increased the soil solution pH from 5 to a maximum value of 7 in the upper portion of the column. In contrast, the fulvate, calcium chloride and phosphogypsum solutions had little effect on soil-solution pH. Treatment with calcium citrate, or fulvate solution that contained 51 mm Na, removed most of the exchangeable aluminium from the column. The cation exchange sites in the upper portion of the column were saturated with calcium, and the cation exchange capacity of the soil was increased from 35 to c. 80 mmol_c kg^?1 in the calcium citrate treatment. Leachate from this treatment contained low (< 2 mm ) calcium concentrations and high aluminium concentrations. In contrast, the above changes were not shown by the calcium chloride and phosphogypsum treatments. In these treatments the calcium concentration in the leachate was equal to that in the inflowing solution, which indicated that calcium was transported through the entire column. These results suggest that calcium alone was ineffective in displacing aluminium from the cation exchange sites and a strong complexing agent such as citrate or fulvate is needed to mobilize the exchangeable aluminium.     

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.     

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.     

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.     

Mechanism of reduction of exchangeable aluminum by gypsum application in acid andosols

Mechanism of reduction of exchangeable aluminum in acid Andosols treated with gypsum was studied by using cation exchange resin methods to determine the amount of polymerized aluminum. Two types of acid Andosols were used as test soils: Kitakami light colored Andosol (fine, mixed, mesic, Andic Dystrochrept) and Kawatabi thick high humic Andosol (medial, mesic mixed Alic Pachic Melanudand). Polymerization of aluminum in the soil solution of both Kitakami and Kawatabi Andosols treated with gypsum was suggested based on an analysis using cation exchange resin methods, whereas that in monomer aluminum solution was not detected. Accumulation of polymerized aluminum in both Kitakami and Kawatabi Andosols was determined by using cation exchange resin, and the amounts of polymer aluminum trapped by the resin and the ratio of polymer aluminum to monomer aluminum were increased with the incubation time. The values of CEC which decreased in the Kitakami Andosol after gypsum treatment were almost equivalent to the amounts of cation exchange sites occupied by polymer aluminum ions which were calculated based on the decrease of the values of Y _l. We conclude that the mechanism of reduction of exchangeable aluminum in strongly acid Andosols treated with gypsum is as follows: firstly, exchangeable aluminum adsorbed on the cation exchange sites of soils may be released into the soil solution due to the increase in the ion strength caused by gypsum application, and then monomer aluminum in soil solution may be polymerized in the presence of soil colloidal materials. Consequently, the polymer aluminum formed in the soil solution may be selectively and irreversibly fixed on the cation exchange sites of 2 : 1 clay minerals.     

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.     

Apparent Cation – Exchange Equilibria and Aluminium Solubility in Solutions Obtained from Two Acidic Forest Soils by Centrifuge Drainage Method and Suction Lysimeters

Apparent cation–exchange equilibria and solubility of aluminium were analysed in two acidic forest soils: a Cambisol and a Cambic Podzol. Soil solution was obtained by a centrifuge drainage method from fresh soil samples and with suction lysimeters. The total positive charge of the measured cations as well as the concentrations of the cations were generally much larger in the centrifugates than in the lysimeter solutions, which implies that total charge of soil solution is larger in small pores than in large pores. Hydrogen ion in particular was concentrated in some of the centrifugates, the ratio centrifugate:lysimeter solution being over 10. The total positive charge of the measured cationsdecreased with increasing depth with both methods. Theapparent cation–exchange coefficients K _H-Ca, K _Al-Ca, and K _K-Ca had different values in the methods, and the variation in the cation exchange coefficients was larger in the lysimeter method than in the centrifuging method. The coefficient K _Mg-Ca had similar values in both methods. The results imply that mobile solution could not have cation–exchange equilibria with bulk exchangeable cations in the soils, although solution in small pores seemed to have equilibria. Solubility of Al did not follow the solubility of an Al(OH)₃ phase in the centrifugates, and the centrifugates with a H⁺ activity larger than 60 μmol were undersaturated with respect to the gibbsite. Solubility of Al was between gibbsite and amorphousAl(OH)₃ in the lysimeter solutions. Differencesbetween the centrifugates and the lysimeter solutionsin the ion concentrations and in the apparent chemicalequilibria were similar for both soils studied.     

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.     

Upscaling spatio‐temporal patterns of cation fluxes in acid forest soils

One main problem with current research on spatio‐temporal modeling of ion fluxes in forest soils is the separation of space and time effects in the soil‐monitoring concept. This article describes an approach to overcome this weakness. Time trends of point information on soil‐solution data (base‐cation concentrations and fluxes) are scaled by linking them to soil‐chemical data which is available in higher spatial resolution and can be upscaled to an area base. This approach is based on a combined evaluation of bulk soil and soil‐solution data using both statistical and process‐oriented methods. Multiple‐linear‐regression analyses coupled with geostatistics were developed to predict spatial patterns of exchangeable cation percentages. In a second step, empirical ion‐distribution coefficients were adapted according to Gapon using data of suction‐cup plots and bulk‐soil samples. Seasonally adjusted time‐series data of soil‐solution chemistry were then connected with the maps of the predicted exchangeable‐cation percentages by means of the Gapon equations. This evaluation step provided both time‐ and space‐dependent maps of cation concentrations in the soil solution. Finally, using the results of a water‐budget model it was possible to derive spatio‐temporal patterns of soil cation fluxes. Methodological limitations and the results of verification processes are discussed. The methods described can only be used in acidic soils and should not be used in soil layers rich in humus, since adsorption to C compounds differs from adsorption to clay minerals. The time increments of the models should be not shorter than yearly in order to suppress annual periodicity. Although the Gapon equations were not based on laboratory‐determined exchange solutions at quasi‐equilibrium, but rather on field data from the suction‐cup technique, the exchangeable‐cation percentages showed steady functions of selectivity coefficients. The methods tested at a watershed scale may be flexible enough to be applied at other scales as well.     

Acidiphily in pteridophytes: Assessment of the role of root cation‐exchange properties

The soil preference with respect to soil acidity of Asplenium scolopendrium L., Dryopteris filix‐mas (L.) Schott, Pteridium aquilinum (L.) Kuhn as well as of subspecies of the Asplenium trichomanes L. and Polypodium vulgare L. complexes were studied in relation to root cation‐exchange properties. Data were collected for substrate acidity, soil exchangeable cations, and root cation‐exchange capacity. Acidiphilous pteridophytes were characterized by low cation‐exchange capacities. It is unlikely that cation‐exchange properties protect plants from potentially harmful cations such as aluminium or hydrogen, which are abundant under acid soil conditions, through immobilization. It is postulated that cation‐exchange properties are a secondary adaptation to soil acidity, in addition to major adaptations which determine the apparent soil preference. Possibly, a limited variation in cation‐exchange capacity as a function of soil conditions could prevent harmful interactions of soil exchangeable cations with the cation‐exchange sites, such as displacement of cell wall calcium by aluminium or hydrogen ions in acid soils.     

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.     

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.     

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.