Soil Cation Exchange Research Articles

Nutrient availability and response of sago palm (Metroxylon sago Rottb.) to controlled release N fertilizer on coastal lowland peat in the tropics

Sago palms (Metroxylon sagu Rottb.) growing on peat soils were found to grow more slowly and to show a lower production than palms growing on mineral soils. This difference was related to the physical and chemical constraints of peat soils, which include low bulk density, high acidity, and low N, P, K, Ca, Zn, and Cu levels. In coastal lowland peat soils, the distance from the sea has been found to be an important determinant of soil elemental composition. We predicted that a sufficient supply of N at the rosette stage would improve sago palm growth and that the availability of N in soil to which controlled release N fertilizer was applied might be higher than that in soil treated with soluble fertilizer. To investigate the changes in the nutrient composition of peat soils at various distances from the sea and the effect on sago palm growth, we studied sago palm areas in Indonesia and Malaysia. To observe the influence of N on the growth performance, we also conducted a fertilizer experiment on coastal lowland peat soil in Indonesia. Distance from the sea had no significant effect on the cation concentration in the soil solution (with the exception of Mg) or on the levels of soil-exchangeable cations. No significant differences were observed between the concentrations of exchangeable cations in surface peat soils and those in mature leaves. However, the concentrations of K, Na, and Ca in mature leaves increased significantly with their concentrations in the soil solution. This finding implies that the concentrations of cations in sago palm leaves depend directly on the concentrations of cations in the soil solution. No significant effect of N fertilizers on plant height and leaf formation was observed. N fertilizers applied twice a year did not affect appreciably the foliar concentration of N determined in December 1998 (5 months after the initial application) and December 1999. In June 2000, we detected a significantly higher concentration of N (p < 0.01) in young leaves of the palms treated with LP-100 or urea than in control leaves. However, no significant difference was detected between the LP-100 and urea treatments in the concentration of N in both mature and young leaves. This finding indicated that the concentration of N in sago palm leaves increased with the level of soil-applied N, regardless of whether N was applied as controlled release fertilizer or in the soluble form. We anticipate that a significant difference in the effects of these N fertilizers may occur during the next rainy season, when there should be a considerable loss of soluble N.

Ammonia volatilization from Vertisols

SummaryFarmers want to minimize losses of nitrogen (N) by volatilization of ammonia when adding fertilizers and improve fertilizer recovery of N by plants. We aimed to quantify the losses of N through NH3 volatilization as affected by soil moisture content, type of fertilizer, and placement method in Vertisols in Kenya, and conducted three experiments for the purpose under controlled conditions in the laboratory. We found that NH3‐N losses were greatest at 80% water holding capacity, which we ascribed to the ready availability of water to dissolve the fertilizer at that water content. The soil's cation exchange capacity (CEC) did not influence volatilization, whereas the soil's pH indicated the potential of the soil to volatilize ammonia. Ammonia losses from the fertilizers were in the order urea &gt; ammonium sulphate &gt; ammonium nitrate applied. Incorporating fertilizer within the 0–5 cm soil layer more than halved NH3 volatilization but did not prevent it completely. These results indicate that soil pH, rather than CEC, is the main inherent characteristic influencing ammonia volatilization from Vertisols. Ammonium‐based fertilizers should be incorporated within the 0–5 cm soil layer, or preferably somewhat deeper, to avoid losses via NH3 volatilization, particularly in alkaline soils. Nitrate fertilizers are preferable to urea where the risks of NH3 volatilization are large, provided due consideration is given to denitrification risks.

Soil acidification as influenced by crop rotations, stubble management, and application of nitrogenous fertiliser, Tarlee, South Australia

Soil acidification, as influenced by N fertiliser, stubble management, and crop rotations, was investigated using soil samples from a long-term rotation trial at Tarlee, South Australia. With the effects of combination of treatment inputs (wheat–lupin, stubble retention and N-fertiliser application), the pHCa (0–10 cm depth) declined from the starting value of 6.12 to 4.50 after a 14-year period. All of the treatments caused the soil pH to decrease. The mean acidification rates for the period 1978–1992 varied from 0.5 to 2.22 kmol H+/ha.year for different treatments. Although the rainfall at Tarlee (483 mm) is not sufficient to cause regular drainage events, it is likely that downward movement of NO3– in the soil profile has caused acidification in the surface soil. Also the retention of stubble caused more acidification than where there was regular stubble burning or removal. The acidification resulted in an increase in soil exchangeable Al and Mn and extractable Al and Mn, and the decrease in soil exchangeable base cations. The values for soluble Al (extracted in CaCl2) in 1992 were 1.58 and 2.45 mg/kg (0–10 cm depth) for the wheat–bean and wheat–lupin rotations, but the percentage of Al in the ECEC was low. It is not known whether this acidity has any impact on yields of field crops at this stage. But with soluble Al and the percentage of Al in ECEC increasing, it is possible that Al toxicity may occur in the high input-output cropping soils in South Australia. acidity, pH, aluminium, manganese.

Efeito residual da adubação com composto orgânico sobre o crescimento e produção de alface

Este trabalho teve como objetivo avaliar o efeito residual do composto orgânico sobre o crescimento e a produção da alface. Plantas da cultivar Babá foram adubadas com cinco doses de composto orgânico (0,0, 22,8, 45,6, 68,4 e 91,2 t/ha de matéria seca), na presença e na ausência de adubo mineral (643 kg/ha de 4-14-8 e duas aplicações de 30 kg/ha de N em cobertura). O efeito residual foi avaliado em um segundo cultivo nas mesmas parcelas, sem adição de adubos. Doses crescentes de composto orgânico aumentaram a produção da cultura até 27.367 kg/ha de matéria fresca, obtida na dose mais elevada em plantas cultivadas entre 80 e 110 dias após a aplicação do composto. A aplicação de adubo mineral não apresentou efeito residual. Os efeitos residuais do composto orgânico expressaram-se também pelo aumento linear dos teores de bases trocáveis, de P e da capacidade efetiva de troca de cátions, (CTC) do solo, que atingiram valores de 10,77 cmol c/dm³, 461 mg/dm³ e 11,08 cmol c/dm³, respectivamente.

Potential productivity of aspen cohorts originating from fire, harvesting, and tree-fall gaps on two deposit types in northwestern Quebec

Height growth of trembling aspen (Populus tremuloides Michx.) stands originating from three different disturbance types (fire, clearcut, and tree-fall gap) was compared on two different deposits (glacial till and lacustrine clay) in the Abitibi region in northwestern Quebec using stem analysis techniques. Several soil properties were also measured to investigate relationships between soil properties and aspen growth. Height growth of aspen was not significantly different among stands of different origins, although on both deposits and at all stages of growth, trees originating from fire were the tallest. Differences in total height among stands of different origins were less than 3 m at 50 years of age. The greatest differences in height growth among stands were expected at younger stages likely because of lower light levels for trees originating from gaps at this stage, but the opposite was observed; height growth differences for 5-year intervals were greater for taller trees. Height growth was greater on clay than on till soils but only for trees greater than 15 m. Soil pH and availability of nitrogen and calcium were correlated with aspen height growth on till soils, while only exchangeable calcium was related to this property on clay soils. Fire had beneficial effects on soils, because it increased soil pH and exchangeable cations. However, these effects did not significantly affect tree growth over one or two rotations.

Effects of reduced atmospheric deposition on soil solution chemistry and elemental contents of spruce needles in NE—Bavaria, Germany

The decrease in anthropogenic deposition, namely SO42- and SO2, in European forest ecosystems during the last 20 years has raised questions concerning the recovery of forest ecosystems. The aim of this study was to evaluate if the long term data of element concentrations at the Fichtelgebirge (NE-Bavaria, Germany) monitoring site indicates a relationship between the nutrient content of needles and the state of soil solution acidity. The soil at the site is very acidic and has relatively small pools of exchangeable Ca and Mg. The trees show medium to severe nutrient deficiency symptoms such as needle loss and needle yellowing. The Ca and Mg concentrations in throughfall decreased significantly during the last 12 years parallel to the significant decline in the throughfall of H+ and SO42- concentrations. Soil solution concentrations of SO42-, Ca and Mg generally decreased while the pH value remained stable. Aluminum concentrations decreased slightly, but only at a depth of 90 cm. Simultaneously a decrease in the molar Ca/Al and Mg/Al ratios in the soil solution was observed. Ca and Mg contents in the spruce needles decreased, emphasizing the relevance of soil solution changes for tree nutrition. The reasons for the delay in ecosystem recovery are due to a combination of the following two factors: (1) the continued high concentrations of NO3— and SO42— in the soil solution leading to high Al concentrations and low pH values and, (2) the decreased rates of Ca and Mg deposition cause a correlated decrease in the concentration of Ca and Mg in the soil solution, since little Ca and Mg is present in the soil's exchangeable cation pools. It is our conclusion that detrimental soil conditions with respect to Mg and Ca nutrition as well as to Al stress are not easily reversed by the decreasing deposition of H+ and SO42—. Thus, forest management is still confronted with the necessity of frequent liming to counteract the nutrient depletion in soils and subsequent nutrient deficiencies in trees.

Time‐dependent zinc desorption in soils

Time dependent zinc (Zn) desorption in eight benchmark soils of India was studied in relation to various pH values and ionic strengths. Soil samples were equilibrated in solutions containing 10 μg Zn g‐1 soil at pH 5.5,6.5, and 7.5 for 48 h at 25±2°C, and adsorbed Zn extracted with calcium chloride (CaCl2) for various periods of time. Desorption of Zn decreased with increasing pH, and the desorption rate decreased abruptly at pH 7.5. In contrast, an increase in the equilibration period and ionic strength of the background electrolyte increased Zn desorption. Four rival kinetic models were fitted and evaluated for their suitability for describing the Zn desorption process. Reaction rate constant (ß) calculated from the Elovich model for the different soils ranged from 9.99 to 25 (mg Zn kg‐1)‐1. The different kinetic models tested indicated that Zn desorption in soils was a diffusion controlled process. The desorption was rapid in the first 4 h, followed by slower phase in the rest of the time at all the pH values indicating a biphasic desorption, characteristic of a diffusion controlled process. The ß value for the Elovich equation showed a strong association with soil clay content and cation exchange capacity (CEC). Further, the best prediction of Zn desorption reaction rate constant could be made using multiple‐regression equation with soil clay content and CEC as variables.

Simulated effects of temperature and precipitation change in several forest ecosystems

The Nutrient Cycling Model (NuCM) was used to investigate the effects of increased temperature (+4°C) and changing precipitation (increased and decreased) on biogeochemical cycling at six forest sites in the United States: a Picea rubens forest at Nolan Divide in the Great Smoky Mountains, North Carolina; mixed deciduous forests at Walker Branch, Tennessee and Coweeta, North Carolina; a Pinus taeda forest at Duke, North Carolina; a P. eliottii forest at Bradford, Florida; and a P. contorta/P. jeffreyii forest at Little Valley, Nevada. Simulations of increased temperature indicated increased evapotranspiration and reduced water flux. Simulations of changes in precipitation indicated disproportionately large variations in soil water flux because of the relative stability of evapotranspiration with changes in precipitation. Increased temperature caused N release from forest floors at all sites. At the N-saturated Nolan Divide site, this resulted in no change in N uptake or growth but increased soil solution Al and NO 3 − and increased N leaching losses. At the N-limited sites, the release of N from the forest floor caused increased growth, and, in some cases, increased NO 3 − leaching as well, indicating that N released from the forest floor was not efficiently taken up by the vegetation. Increased precipitation caused increased growth, and decreased precipitation caused reduced growth in the N-limited sites because of changes in wet N deposition. Changes in precipitation had no effect on growth in the N-saturated Nolan Divide site, but did cause large changes in soil solution mineral acid anion and Al concentrations. Increased precipitation caused long-term decreases in soil exchangeable base cations in most cases because of the disproportionately large effects on soil water flux; however, increased precipitation caused decreases in exchangeable base cations in cases where atmospheric deposition was a major source of base cations for the system. The simulation results illustrate the extreme complexity of the possible responses of nutrient cycling processes to climate change. By virtue of the fact that the NuCM model does not contain physiological algorithms, these simulations demonstrate that changes in temperature and precipitation can produce widely varying ecosystem-level responses through their effects on biogeochemical cycling processes alone and that generalizations about the relative importance of temperature versus precipitation changes are hazardous.

The distribution of solute processes on an acid hillslope and the delivery of solutes to a stream: II. Exchangeable Al3+

This paper aims to identify the spatial distribution of exchangeable base cations in soils on an acid hillslope and to investigate possible cation release processes from slope soils to the stream. The basic assumption underlying this research is that the amount of exchangeable cations in soils reflects the nutrient stores and cation leaching processes across the slope where vegetation and parent materials are similar. The distribution of exchangeable Ca2+, Mg2+, K+ and Na+ has been investigated on a three-dimensional hillslope on the Quantock Hills, Somerset, UK. A two-way ANOVA shows that soil depth is predominant in explaining the total variance of exchangeable bases, despite the steep slope gradient and clear podzolic catena development. Major nutrient base cations, such as Ca2+, Mg2+ and K+, display homogeneous topsoil storage right across the slope. This spatial pattern may indicate that the spatial distribution of major nutrient cations is tightly controlled by the soil–vegetation system in nutrient-poor heathland environments. Na+ is an exception to this vegetation-controlled spatial distribution, because of its small involvement in the soil–vegetation and soil exchangeable systems. In subsurface soils, cations liberated from the soil–vegetation system are subject to redistribution over the slope according to the hydrological flowpaths operating on the slope, with some eventually released into the stream. The saturated wedge developed at the base of the slope plays a key role in the storage and release processes of base cations from slope soils to the stream. Ca2+, Mg2+ and Na+ carried by throughflow are stored in the saturated wedge and gradually released into the stream at times of high flow. K+, however, shows an apparently different spatial behaviour, being deficient in the saturated wedge. Copyright © 1999 John Wiley & Sons, Ltd.

The distribution of solute processes on an acid hillslope and the delivery of solutes to a stream: I. Exchangeable bases

This paper aims to identify the spatial distribution of exchangeable base cations in soils on an acid hillslope and to investigate possible cation release processes from slope soils to the stream. The basic assumption underlying this research is that the amount of exchangeable cations in soils reflects the nutrient stores and cation leaching processes across the slope where vegetation and parent materials are similar. The distribution of exchangeable Ca2+, Mg2+, K+ and Na+ has been investigated on a three-dimensional hillslope on the Quantock Hills, Somerset, UK. A two-way ANOVA shows that soil depth is predominant in explaining the total variance of exchangeable bases, despite the steep slope gradient and clear podzolic catena development. Major nutrient base cations, such as Ca2+, Mg2+ and K+, display homogeneous topsoil storage right across the slope. This spatial pattern may indicate that the spatial distribution of major nutrient cations is tightly controlled by the soil–vegetation system in nutrient-poor heathland environments. Na+ is an exception to this vegetation-controlled spatial distribution, because of its small involvement in the soil–vegetation and soil exchangeable systems. In subsurface soils, cations liberated from the soil–vegetation system are subject to redistribution over the slope according to the hydrological flowpaths operating on the slope, with some eventually released into the stream. The saturated wedge developed at the base of the slope plays a key role in the storage and release processes of base cations from slope soils to the stream. Ca2+, Mg2+ and Na+ carried by throughflow are stored in the saturated wedge and gradually released into the stream at times of high flow. K+, however, shows an apparently different spatial behaviour, being deficient in the saturated wedge. Copyright © 1999 John Wiley & Sons, Ltd.

A comparison of methods for gypsum requirement of brine-contaminated soils

An estimate of the gypsum requirement (GR) of soils affected by Na salts has practical value. The estimated GR can indicate both the quantity of any Ca amendment needed and the progress of site remediation. Four published methods to estimate GR use analytical results that do not directly include any Na in excess of the soil's cation exchange capacity (CEC). GR values thus obtained, for a 15-cm soil layer, are at most 20 to 50 t ha−1. We used these four methods to calculate the GR for various soils with known, differing salt contents. The values obtained were often inconsistent with the sodium adsorption ratio (SAR) and electrical conductivity (EC), parameters that indicate the severity of site-contamination. We also used an unpublished method to estimate GR from the amount of Ca required to bring each soil's SAR down to a threshold value of 7, on the basis of concentrations of soluble ions in a saturated paste filtrate. Estimates of GR made in this way often exceeded 50 t ha−1, but were consistent with SAR and EC levels at the various sites. This method may be more appropriate for estimating GR after brine spills on soils where Na is not readily leached and the quantity of Na exceeds the CEC. This situation often applies on the Canadian prairies. Estimating GR from the quantity of Ca required to replace exchangeable Na may be appropriate for sodic, free-draining soils in areas with high rainfall, or on irrigated land. Key words: Gypsum requirement, salt contamination, sodium adsorbtion ratio, electrical conductivity, formation water

Importance of soil exchangeable cations and aluminium content on land snail distribution

The influence of soil exchangeable cations and aluminium content on the distribution of various terrestrial gastropods was investigated. Calcium was the most important factor, though aluminium and magnesium content also had some effect. Potassium and sodium had no significant influence on distribution. The species most sensitive to the factors analysed were Cochlicopa lubrica, Vertigo pygmaea and Carychium tridentatum.

The potassium status of some pacific island soils

The potassium (K) status of 22 soil samples from 12 pedons originating in 6 Pacific Island countries has been investigated by several techniques. The total K contents of the soils studied were found to be low to very low. Use of various methods available for measuring exchangeable cations in soils showed exchangeable K to be dependent on factors such as ionic strength and displacement cation of the extracting solution. The proportions of non‐exchangeable K that are plant available were found to be very low for most soils. Data obtained from quantity/intensity measurements suggest that the soils would be responsive to added K.

Changes in soil mineralogy and exchangeable cation pools in stands of Norway spruce planted on former pasture land

Chemical and mineralogical properties of the soils in 35- and 70-year-old stands of Norway spruce (Picea abies (L.) Karst), planted on former pasture and were studied at Asa Experimental Forest, southern Sweden. Remnant deciduous forests bordering the spruce stands were used as controls to assess possible tree-species-related effects on soil development. All soils are acid with little difference in soil pH between the spruce and deciduous stands. However, the saturation of the exchange complex with Mg is lower beneath spruce and the total exchangeable Mg pool in the upper meter of these soils is one third of the Mg store beneath the deciduous stands. Amphibole, biotite and chlorite are the major sources of Mg in the parent soil. The clay fraction of the topsoil beneath spruce has been depleted of all these easily weatherable ferromagnesian minerals. Apart from weathering-resistant primary silicates, the clay fraction consists almost exclusively of expandable, smectitic mixed-layer minerals, which are believed to be the products of advanced stages of biotite weathering. In contrast, vermiculite is the dominant secondary mineral in the A-horizon in the deciduous stands, and some chlorite has survived. Moreover, a greater depth of in situ weathering is indicated for the soil of the old spruce stands where biotite/vermiculite mixed-layers have formed in the C-horizon as products of early stages of biotite weathering. Thus, differences between the paired sites in soil solution chemistry are supported by the qualitative differences in soil mineralogy, and are believed to reflect divergent biotic and/or abiotic processes in the different stand types.

Mulching effect of plant residues of chemically contrasting compositions on soil organic matter content and cation exchange capacity

Effects of five types of plant residues [Acioa, presently Dactyladenia barteri, Gliricidia sepium, and Leucaena lecocephala prunings, maize (Zea mays) stover and rice (Oryza sativa) straw] applied as mulch on soil organic matter (SOM) content and effective cation exchange capacity (ECEC) were studied on an Alfisol in the humid tropics. Plant residue mulch resulted in a decline in SOM and ECEC during two years of cropping following six years of grass fallow. Rice straw mulch resulted in less and maize stover mulch in a greater decrease of SOM and ECEC than the other mulches. Decrease in SOM and ECEC is attributed to the mulching effect on the soil micro‐climate which enhanced the decomposition of SOM accumulated during the grass fallow prior to the initiation of the experiment. In order to maintain SOM for a tropical soil, plant residues with high lignin, polyphenols, and silica will have to be among residue species when applied in continuous cropping systems.

Sources and controls of calcium and magnesium in storm runoff: the role of groundwater and ion exchange reactions along water flowpaths

Abstract. A combined hydrological and chemical investigation was undertaken in a small moorland catchment at Plynlimon to determine the processes controlling storm runoff chemistry. Flow from natural soil pipes, overland flow from peat soils, throughflow from a mineral horizon and streamflow were gauged and sampled intensively during seven storms. Stormflow Ca and Mg concentrations in stream water consistently exceeded those observed in overland flow, pipeflow and throughflow. The response of Ca and Mg to increases in streamflow varied between the storms and could not be explained readily by the mixing of the dominant source waters monitored within the catchment. Intensive sampling of pipe water along a major stormflow pathway revealed a large and consistent increase in the concentration of dissolved Ca and Mg accompanied by a corresponding decrease in acidity, the magnitude of which was strongly influenced by antecedent conditions. Analyses of soil exchangeable cations along the stormflow pathway revealed soils enriched in divalent cations probably derived from a groundwater source. Laboratory leaching experiments confirmed that rapid cation exchange reactions could explain the changes in pipe water chemistry along the stormflow pathway. The relative contribution of flow from pathways where these ion exchange reactions occur strongly influences the stormflow response of Ca and Mg in the stream. The results also highlight a potentially important, indirect role for base-rich groundwater in modifying storm runoff chemistry along water flowpaths.

Integrating variations of soil-adsorbed cations into a cation exchange model

A computer simulation of cation exchange reactions in heterogeneous soils is provided. It is used to examine the relationships between theoretical cation exchange equations and lumped cation concentrations for acid organic horizons of podzolic, peat and shallow organic soils. The study is based around field data for exchangeable cations at the Birkenes catchment in southern Norway. Field measurements of the relative proportions of soil exchangeable cations show substantial variation and correspond to a wide range of micropore water chemistries. Spatial and temporal heterogeneity is introduced in the simulations to represent natural variation in both hydrological conditions and exchangeable cation proportions. Modelled results show that heterogeneity in soil-adsorbed cation ratios results in highly scattered relationships between cations in the soil-micropore water, with contrasting behaviours at low and high anion concentrations. At low anion concentrations, hydrogen-ion and sodium concentrations are negatively correlated, whilst poor correlations are observed for the more highly charged cations. At high anion concentrations, no pair of cations dominates the total cation charge and relationships are much more scattered. Despite this, any alteration of anion concentration results in a systematic change in average cation concentrations. Similar patterns are observed when further heterogeneity is introduced by varying the local micropore equilibrium constants for the exchange reactions. The averaged or lumped data approximately follow laws analogous to the micropore cation exchange formulations. However, as the degree of heterogeneity increases, so too does the extent of the deviation away from the behaviour of a purely homogeneous system. At a gross level, the inter-relationships of cations of different charge become more linear with increasing heterogeneity. The results, in conjunction with two earlier companion papers, provide: (1) a method allowing the effects of heterogeneity to be investigated for cation exchange reactions; and (2) strong justification for the continued practice of lumping techniques in catchment scale hydrochemical models.

A comparison between three methods for the determination of cation exchange capacity and exchangeable cations in soils

L'objet de cet article est de comparer les resultats obtenus au moyen de trois methodes normalisees de determination de la capacite d'echange cationique des sols (CEC) et des cations echangeables (Ca, Mg, K). Les methodes examinees utilisent des reactifs d'echange differents : le chlorure de cobaltihexammine, le chlorure de baryum et l'acetate d'ammonium. Les procedures d'echange varient egalement : ce sont, la simple agitation, les extractions successives et la percolation. Les teneurs mesurees avec le chlorure de baryum et le chlorure de cobaltihexammine sont etroitement correlees et montrent l'uniformite des processus physicochimiques mis en jeu. De ce point de vue, les deux methodes peuvent etre considerees comme equivalentes. L'acetate d'ammonium, en tamponnant le pH du milieu d'extraction, induit des variations importantes dans les proportions de sites electronegatifs et en particulier, ceux lies a la matiere organique. La prise en compte du pH et de la teneur en carbone des echantillons nous a cependant permis de reduire les differences entre methodes. Les quantites de calcium et de potassium extraites varient egalement a cause de la dissolution d'especes carbonatees et l'aptitude particuliere de l'ammonium a s'echanger avec le potassium.

Determination of cation exchange capacity and exchangeable cations in soils by means of cobalt hexamine trichloride. Effects of experimental conditions

On decrit et compare differentes manieres d'utiliser des solutions de chlorure de cobaltihexammine [Co(NH 3 ) 6 ]CI 3 pour mesurer la capacite d'echange cationique (CEC) et les quantites de cations echangeables d'un echantillon de sol. On decrit dans un premier temps differentes techniques de dosage de l'ion cobaltihexammine en solution. Le cobalt peut etre dose par absorption atomique de flamme et l'ion ammonium par spectrocolorimetrie. Neanmoins, la spectrocolorimetrie directe des solutions de cobaltihexammine presente les avantages d'une grande simplicite de mise en oeuvre et d'une bonne repetabilite, sous reserve que l'on s'affranchisse correctement des absorptions non specifiques. Elle a ete retenue pour comparer differentes procedures d'echange entre l'echantillon de sol et la solution de reactif: la simple agitation, les extractions successives et la percolation. Cette etude, en decrivant l'influence de certains parametres experimentaux importants, permet de justifier le choix d'une procedure particuliere en precisant ses limites d'utilisation, ses avantages et ses inconvenients. Malgre un rendement legerement plus faible, les resultats obtenus avec une simple agitation restent tout a fait appropries pour mesurer l'amplitude des reactions d'echange.

Role of the dwarf bamboo (Sasa) community in retaining basic cations in soil and preventing soil acidification in mountainous areas of Japan

Adjacent plots (1 m2) with and without communities of dwarf bamboo (Sasa), i.e. Sasa- and ref-plots, were selected in mountainous areas, which were relatively low in soil buffer capacity. The following parameters were studied: chemical properties of surface (0-30 cm) soil (at 6 sites), elemental abundances in the soil-Sasa ecosystem (at 6 sites), effect of artificial acid rain on the above two parameters (at 1 site), and chemical properties of throughfall and stemflow of Sasa (at 2 sites including one on a plain). Average values of pH(H2O), base saturation and the ratio of exchangeable (K+Mg+Ca)/exchangeable Al in surface soil were 4.35±0. 53, 25.2±14.3% and 0.41±0.28, respectively, in Sasa-plots and 4.26±0.63, 20.0±9.6%, and 0.28±0.13, respectively, in ref-plots. Though not significant, all soil parameters had higher values in Sasa-plots, i.e. Δx = ca. 0.1 unit, 5% and 0.13, respectively. When the abundance of elements (exchangeable cations in soil of 30 cm depth plus elements in litter and Sasa biomass) in the ecosystem was compared between the two plots, K (and often other basic cations) was higher in Sasa-plots than in ref-plots, whereas Al was lower. Artificial acid rain (1.5 L of 0.05 M H2SO4 applied monthly for 10 months) induced a reduction of Na, K, Mg and Ca in a ref-plot, but in a Sasa-plot only Na and K were reduced whereas Mg and Ca were completely retained. The composite samples of throughfall and stemflow of Sasa were ca. 0.5 higher in pH and richer in K, Mg and Ca than the ambient precipitation. The amounts (equivalents) of elements released by Sasa were in the order K > Ca > Mg. It was determined that about 87% and 98% of K, 76% and 87% of Ca, and 39% and 93% of Mg were of Sasa origin in the composite samples at a mountainous site (cambisol soil type) and a plain site (andosol soil type), respectively. Sasa communities may have a significant role in retention of basic cations in surface soil and prevention of soil acidification because of recycling elements in the soil-Sasa ecosystem.