Mechanisms of fixation and release of ammonium in paddy soils after flooding III. Effect of the oxidation state of octahedral Fe on ammonium fixation

An experiment with two typical paddy soils from China and two clay minerals was conducted to study the effect of reduction of octahedral Fe^III on fixation of NH₄⁺ ions. Reduction of octahedral Fe^III was achieved by treating soils and clay minerals with dithionite‐citrate‐bicarbonate (DCB) followed by dialyzing the samples under oxygen free conditions. Reduction of Fe^III increased the negative charge of interlayers and resulted in a significantly higher ammonium fixation. Close positive correlations were found between the Fe²⁺ concentration or the ratio of Fe²⁺/Fe³⁺ and non‐exchangeable NH₄⁺‐N. Therefore, it is concluded that the reduction of octahedral Fe induced by flooding is one of the important prerequisites for the pronounced ammonium fixation in flooded soils. However, the relation between ΔFe²⁺ and Δfix‐N was not stoichiometric.     

Erratum

Abstract

Phosphorus fixation in soil occurs mainly in the clay fraction, the mineralogical nature of which varies widely. Phosphorus sorption characteristics of 14 soil clays having divergent mineral compositions have been studied with P concentrations approximating those in fertilized soils, because insufficient data were found in the literature on the role of various soil clay mineral species in P fixation. The results show that clays with dominant Kaolinite or halloysite fix more than 75 percent of the applied P; followed by those with major Kaolinite or halloysite or dominant x‐ray amorphous materials (60–70% fixation). Beidellitic clays fix more P (50%) than montmorillonitic clays (45%), which in turn sorb more P than vermiculitic clays (29%).     

Extraction of potassium from some kaolinitic soils of the tropics

Abstract

Three methods for soil potassium extraction (M NH₄OAc pH 7, 0.01 M AgTU and 30 % hot H₂SO₄) were compared for a variety of kaolinitic soils of the tropics. The AgTU‐extractable K was much higher than the M NH₄OAc‐extractable K when vermiculite clay was present in the soil. The correlation between both was given by an R value of 0.937. The amounts of K extracted by 0.01 M AgTU and by hot H₂SO₄ were approximately the same. The R value for these two methods was 0.843.

It is suggested that the AgTU extractant could be used for determination of plant‐available K in soil and for testing for the presence or absence of vermiculite clay in soils.     

Fixation of zinc by some rice soil clays under upland conditions

Abstract

Because of widespread Zn deficiency in rice, an experiment was designed to evaluate the Zn fixing capacity of several clay minerals separated from tropical rice soils. The study involved the addition of 25 μg Zn per g of clay as zinc sulphate, incubation at an ambient temperature of 30 C±2 followed by alternate wetting and drying and extraction by 0.005 M DTPA to assess the magnitude of Zn fixation.

On average, 57% of the applied Zn was unextractable by 0.005 M DTPA and considered fixed. The dominantly biedellite clay systems possessed the highest capacity to fix Zn (70%), followed by vermiculite (59%) and montmori‐llonite (55%). Clay systems containing hydrous mica impregnated with important proportions of kaolinitic and vermiculitic type minerals fixed 40% of the added Zn. Most of the clays, consisting of mixed mineralogy, fixed more than 50% of the applied Zn.     

Influence of Aluminum Hydroxide on Potassium Release from Two Colombian Soils

Abstract

The effect of sesquioxides on the mechanisms of chemical reactions that govern the transformation between exchangeable potassium (Kex) and non‐exchangeable K (Knex) was studied on acid tropical soils from Colombia: Caribia with predominantly 2∶1 clay minerals and High Terrace with predominantly 1∶1 clay minerals and sesquioxides. Illite and vermiculite are the main clay minerals in Caribia followed by kaolinite, gibbsite, and plagioclase, and kaolinite is the major clay mineral in High Terrace followed by hydroxyl‐Al interlayered vermiculite, quartz, and pyrophyllite. The soils have 1.8 and 0.5% of K₂O, respectively. They were used either untreated or prepared by adding AlCl₃ and NaOH, which produced aluminum hydroxide. The soils were percolated continuously with 10 mM NH₄OAc at pH 7.0 and 10 mM CaCl₂ at pH 5.8 for 120 h at 6 mL h^?1 to examine the release of Kex and Knex. In the untreated soils, NH₄ ⁺ and Ca²⁺ released the same amounts of Kex from Caribia, whereas NH₄ ⁺ released about twice as much Kex as Ca²⁺ from High Terrace. This study proposes that the small ionic size of NH₄ ⁺ (0.54 nm) enables it to enter more easily into the K sites at the broken edges of the kaolinite where Ca²⁺ (0.96 nm) cannot have access. As expected for a soil dominated by 2∶1 clay minerals, Ca²⁺ caused Knex to be released from Caribia with no release by NH₄ ⁺. No Knex was released by either ion from High Terrace. After treatment with aluminum hydroxide, K release from the exchangeable fraction was reduced in Caribia due to the blocking of the exchange sites but release of Knex was not affected. The treatment increased the amount of Kex released from the High Terrace soil and the release of Knex remained negligible although with Ca²⁺ the distinction between Kex and Knex was unclear. The increase in Kex was attributed to the initially acidic conditions produced by adding AlCl₃ which may have dissolved interlayered aluminum hydroxide from the vermiculite present, thus exposing trapped K as exchangeable K. The subsequent precipitation of aluminum hydroxide when NaOH was added did not interfere with the release of this K, and so was probably formed mostly on the surface of the dominant kaolinite. Measurement of availability of K by standard methods using NH₄ salts could result in overestimates in High Terrace and this may be a more general shortcoming of the methods in kaolinitic soils.     

Semiquantitative determination of imogolite and Al-rich allophane (Si / Al ≃ 1 : 2) in some volcanic ash soils in San'in region by a combination of thermogravimetry-differential thermal analysis and trimethylsilylation analysis of soil clays

Abstract

A method to determine the contents of imogolite and Al-rich allophane (Sil Al ? 1 : 2) in volcanic ash soils was presented. The method is based on the (1) assessment of the presence of Al-rich allophane in clays by successsive extraction with dithionite-citrate and oxalate-oxalic acid, (2) trimethylsilylation of soil clay with a mixture of hexamethyldisiloxane, HCl, and isopropyl alcohol, and determination of the content of monomeric Si based on the trimethylsilyl derivative of monomeric orthosilicate anion by gas / liquid chromatography, (3) determination of the total content of imogolite and Al-rich allophane based on the content of monomeric Si from imogolite, (4) determination of the imogolite content by Thermogravimetry (TG )-Differential Thermal Analysis (DTA) based on the weight loss due to endothermic dehydroxylation with maximum values at ca. 386°C, (5) calculation of the Al-rich allophane content by subtracting the imogolite content from the total content of these minerals, and (6) evaluation of the imogolite and Al-rich allophane content of soil by multiplying clay content of soil and the two mineral content of clay. The trimethylsilylation analysis was found to be reproducible, and the estimated total amounts of two minerals in clays by this method were adequately approximated to those evaluated from the amount of Si (= Si_o) extracted with oxalate-oxalic acid after extraction with dithionite-citrate. The variation in the abmldance of two minerals in the soil horizons of volcanic ash soils from the San'in region indicated that this method is suitable for the profile-study of volcanic ash soils.     

Ammonium fixation by soil and pure clay minerals

Abstract

Fixation of the ammonium ion (NH₄ ⁺) by clay minerals is an alternate way of building the nitrogen (N) pool in soil to optimize N crop recovery and minimize losses. Clay minerals (illite, montmorillonite, and vermiculite) and an illitic Portnoeuf soil were used to compare NH₄ ⁺ fixation abilities. Total N determination and X‐ray diffraction analysis were performed on each of the minerals and the Portnoeuf soil controls, and NH₄ ⁺ saturated batches were subsequently desorbed by potassium chloride (KCl) after 4096 hours. Total N was determined for each employing either Kjeldahl digestion only, or pretreating with hydrofluoric‐hydrochloric acid (HF‐HCl) before the Kjeldahl digestion. The total N for the soil was 38% more after pretreatment with HF‐HCl. The total N determined after pretreatment with HF‐HCl for the NH₄ ⁺ saturated and subsequently KCl desorbed minerals was found to be highest in vermiculite. The cation exchange acapacity (CEC) of each of the minerals was determined, and highest CEC was found in montmorillonite [83.07 cmol(+)/kg]. X‐ray diffraction analysis revealed collapse of the vermiculitic clay lattice from an initial d‐spacing of 13.1 angstrom to 10.4 angstrom after desorprion by KCl. This suggested the existence of sequestered NH₄ ⁺ between the 2: 1 vermiculitic clay interlayer lattice.     

Chloritization in lowland paddy soils

This paper is concerned with the alteration of clay minerals which takes place when well-aerated lowland soils (Brown lowland soils) are cultivated for growing rice. For this purpose the clay mineral compositions of paddy soils were compared with those of adjacent arable soils at four locations.

In the case of arable soils a larger part of the 14Å spacings collapsed to 10Å on treatment with NH₄NO₃ solution, or on drying at about 100°C, whereas in paddy soils the spacings were more stable to thelie treatments. Cation exchange capacities of clays were always smaller In paddy soils than in arable soils. Alternate treatments of reduction and oxidation somewhat increased the stability of the 14Å spacings to heat treatment.

These results indicate that chloritization is a very common process occurring in lowland paddy sons. Chloritization In paddy soils appears to be closely associated with the seasonal cycle of reduction and oxidation.     

Quantities of potassium fertilizer required to raise soil test value

Abstract

In order to calculate the potassium (K) fertilizer requirement, it is necessary to know how much of this nutrient element must be applied in order to overcome any buffering effects and raise the soil test value to a desired level. A glasshouse study was conducted on a wide range of KwaZulu‐Natal (South Africa) soils to establish this information. The topsoil (0–200 mm) at 51 sites was sampled. Soils varied greatly in texture (4–83% clay), organic carbon (0.2–9.2%), and clay mineralogy (kaolinitic‐sesquioxic through to illitic and smectitic). Soil from each site was treated with four levels of K and taken through three wetting and drying cycles over a six‐week period. Analysis for K using the “Ambic”; [ammonium bicarbonate (NH₄HCO₃)/ammonium fluoride (NH₄F)/EDTA] extractant showed that the quantity of applied K (kg ha^‐1) required to raise the soil test value by a unit (1 mg L^‐1), i.e., the K requirement factor, varied between 1.5 and 8.8. Therefore, on soils that display the highest K fixation, the calculated fertilizer K requirement, which is currently based on a factor of 2.5, could be underestimated by as much as 70%. Clay mineral analysis showed that the higher levels of K fixation tended to be associated with the presence of vermiculite.     

胡敏酸对铵钾在粘土矿物上交互作用的影响

Interaction of ammonium (NH+4) and potassium (K+) is typical in field soils. However, the effects of organic matter on interaction of NH+4 and K+have not been thoroughly investigated. In this study, we examined the changes in major physicochemical properties of three clay minerals (kaolinite, illite, and montmorillonite) after humic acid (HA) coating and evaluated the influences of these changes on the interaction of NH+4 and K+on clay minerals using batch experiments. After HA coating, the cation exchange capacity (CEC) and specific surface area (SSA) of montmorillonite decreased significantly, while little decrease in CEC and SSA occurred in illite and only a slight increase in CEC was found in kaolinite. Humic acid coating significantly increased cation adsorption and preference for NH+4, and this effect was more obvious on clay minerals with a lower CEC. Results of Fourier transform infrared spectrometry analysis showed that HA coating promoted the formation of H-bonds between the adsorbed NH+4 and the organo-mineral complexes. HA coating increased cation fixation capacity on montmorillonite and kaolinite, but the opposite occurred on illite. In addition, HA coating increased the competitiveness of NH+4 on fixation sites. These results showed that HA coating affected both the nature of clay mineral surfaces and the reactions of NH+4 and K+with clay minerals, which might influence the availability of nutrient cations to plants in field soils amended with organic matter.     

Studies on the mechanisms of fixation and release of ammonium in paddy soils after flooding. I. Effect of iron oxides on ammonium fixation

Experiments were conducted with two typical paddy soils from China and a vermiculite to study the influence of iron oxides on the fixation and release of ammonium. Removing iron oxides, especially amorphous iron oxides, from the soils favoured the release of non-exchangeable NH₄-N and stimulated the fixation of NH₄-N in the presence of added (NH₄)₂SO₄. Addition of artificial goethite and hematite to the original soils or to the soils free of iron oxides reduced the fixation of NH₄⁺-ions. This effect was also observed with vermiculite. We conclude that the coating of clay minerals with iron oxides has an impact on the diffusion of NH₄⁺-ions into and out of the interlayers of the clay minerals. The reduction and dissolution of iron oxides induced by low redox potential (E_h) after flooding of paddy soils is assumed to be an important mechanism controlling NH₄⁺-fixation in paddy fields.     

Transformation of clay minerals in nanoparticles of several zonal soils in China

Purpose

Clay minerals significantly affect the physical, chemical, and biological processes of soils. They undergo spontaneous modification and transformation depending to the climatic conditions. Information concerning the compositions and transformation of clay minerals in nanoparticle colloids (NPs) (25–100 nm) is severely lacking. Studying clay mineral transformation is important approach to understand soil formation. This study was conducted to determine the transformation sequence of clay minerals in several zonal soil NPs.

Materials and methods

Four soils (Haplustalf, Alf-1; Hapludalf, Alf-2; Hapludults, Ult-1 and Ult-2) were collected from B horizons developed under three different climatic zones of China. Alf-1 (36° 05′ N and 117° 24′ E) was located under a warm temperate zone and Alf-2 (30° 38′ N and 115° 26′ E), Ult-1 (29° 13′ N and 113° 46′ E), and Ult-2 (19° 27′ N and 109° 17′ E) under a subtropical zone. The clay particles (<?2000 nm) (CPs) and nanoparticles (25–100 nm) (NPs) of tested soils were separated. The element composition of CPs and NPs was identified by microwave digestion method. The mineralogy and chemical bonding of clay minerals were studied by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR).

Results and discussion

With decreasing latitude, NPs and CPs showed that the molar ratio of SiO₂ to Al₂O₃ trends to diminish, indicating the phenomenon of desilication and allitization in the tested soils. XRD analysis revealed that the main clay mineral of Alf-1 NPs was illite, followed by vermiculite, kaolinite, and kaolinite interstratified minerals (KIMs). The clay minerals of Alf-2, Ult-1, and Ult-2 NPs were dominated by kaolinite (and KIMs), followed by illite, with a little content of hydroxyl-interlayered vermiculite (HIV) in Ult-1 NPs and trace content of gibbsite in Ult-2 NPs. With decreasing latitude, vermiculite and HIV decreased in NPs. When compared to CPs, smectite as well as illite-vermiculite mix-layer mineral (I-V) and illite-HIV mix-layer mineral (I-HIV) were not detected in NPs. The analysis of d060 region by XRD showed that with decreasing latitude, the main clay minerals in NPs were dioctahedral minerals (e.g., illite or kaolinite). These clay minerals resulted from the transformation of trioctahedral minerals in CPs. The disappearance of 2:1 swelling minerals and trioctahedral minerals showed that the NPs were more susceptible to weathering than CPs.

Conclusions

With decreasing latitude, the transformation of clay minerals followed the sequence of illite?→?HIV?→?kaolinite?→?gibbsite in tested NPs.

     

Assay of urease enzyme activity in an ammonium‐fixing soil

Abstract

Rates of substrate disappearance and product formation were compared as measures of urease enzyme activity in an NH₄‐fixing and in a non‐fixing soil under tris‐, borate‐ or non‐buffered assay conditions over 4h at 37°C. Tris‐buffered urease activity of the NH₄‐fixing soil was 119 μg urea‐N hydrol./g/h or 116 μg (KCl‐extractable) NH₄‐N/g/h indicating prevention of NH₄ fixation by the buffer; without tris, NH₄ production rates amounted to only 35% of coresponding urea hydrolysis rates. Equal rates of urea disappear‐ ance and NH₄ formation occurred in the non‐fixing soil irrespective of buffer amendment.

Tris‐inhibition of NH₄ fixation during 4h incubation at 37°C, however, depended on NH₄ Cl rate and buffer strength. 0.025–0.10 M tris (pH 9.0) reduced NH₄ fixation to negligible amounts at < 0.03 M NH₄C1 whereas, at 0.06–0.24 M NH₄Cl, substantial NH₄ fixation occurred in the presence of 0.05 M tris; NH₄ fixation in unbuffered soil, however, always exceeded that in tris‐buffered soil. Borate buffer (0.06M, pH 10) did not influence the extent of NH₄ fixation.

Tris significantly enhanced urea hydrolysis in the slightly acid, non‐fixing soil but not in the moderately alkaline NH₄ ‐fixing soil indicating an effect of soil type on pH optima of urease enzyme activity. The urease activities of both soils in borate were considerably lower than in tris, possibly because of the combined effects of excess alkalinity and high substrate concentration.     

Factors affecting potassium fixation in calcareous soils of southern Iran

Potassium fixation capacity and mineralogical analysis of 24 representative soils, collected from southern Iran, were studied. Potassium fixation analysis was performed by adding six rates of K from 0 to 1000 mg kg^?1 soil in a plastic beaker and shaking for 24 h. Mineralogical analysis showed that the clay fractions were dominated by smectite, chlorite, mica, palygorskite, vermiculite and quartz. In general, the studied soils fixed 8.5–55% of the added K. The potassium fixation capacity of the studied soils was significantly correlated with smectite content (r ² = 0.87), clay content (r ² = 0.60), cation-exchange capacity (r ² = 0.79) and NH₄OAc-K. Wetting and drying treatment and incubation time had significant effects on K fixation. The average percentage increase in K fixation following the wetting and drying treatment was 24 and 30% for surface and subsurface soils, respectively. The average percentage increase in K fixation with increasing residence time was 79 and 56% for surface and subsurface soils, respectively. Because K fixation is a diffusion process, time and increased concentration of soluble K (because of soil drying) are factors affecting the rate of K diffusion from a soil solution to the interlayer positions of the expansible 2:1 clay minerals.     

Effect of climate and soil type on the immobilization of nitrogen by decomposing straw in northern and southern Europe

 Wheat straw enclosed in mesh bags was buried for periods up to 1 year over two seasons in Scottish, Danish and Portuguese soils treated with ¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃. Scottish soils were: Terryvale, a poorly drained sandy loam; and Tipperty, an imperfectly drained brown forest soil with a higher clay content. The Danish soil (Foulum) was a freely drained sandy loam and the Portuguese soils were a sandy soil (Evora) and a clay soil (Beja). During the first month, ¹⁵N was being incorporated into the straw in the Tipperty, Terryvale and Foulum soils simultaneously as the total N content was decreasing. Subsequently, the straws began to show net immobilization and the total N content of the original straw was exceeded in Tipperty and Foulum soils after 4 months and 8 months, respectively. Net immobilization in Terryvale was detected only in the second season and did not occur in the first because of high soil moisture content. The rates of ¹⁵N incorporation were similar in the two Portuguese soils, and a loss of N was only detected after 8 months. After 1 month, in the two clay soils, Beja and Tipperty, ¹⁵NO₃ ^– was incorporated into straw to a greater extent than ¹⁵NH₄ ⁺ and this was attributed to ¹⁵NH₄ ⁺ fixation by clay minerals. In contrast, ¹⁵NH₄ ⁺ was more efficiently incorporated than ¹⁵NO₃ ^– under waterlogged conditions (Terryvale) and NO₃ ^– loss could be attributed to denitrification. The proportion of added ¹⁵N in the straw residue after 1 month varied between 6% and 18% for ¹⁵NH₄ ⁺ and 2% and 23% for ¹⁵NO₃ ^– and immobilization of N in the longer term tended to be greater in soils from northern Europe than from Portugal. Received: 19 January 1998     

Verhalten von Dünger-NH4 in Böden unterschiedlicher tonmineralischer Zusammensetzung im Inkubationsversuch

Fate of fertilizer ammonium in soils with different composition of clay minerals in an incubation experiment In an incubation experiment with three different soils (gray brown podsolic soil from loess, alluvial gley, and brown earth, derived from basalt) the specific adsorption (fixation) and release of fertilizer NH₄⁺ was investigated. In one treatment 120 mg NH₄–N/kg soil was added, while the other treatment (control) received no nitrogen. Soils samples were taken every ten days and analyzed for nonexchangeable and exchangeable NH₄⁺ and NO₃^?. The experimental results are showing that the specific adsorption of applied NH₄⁺ was related to the type of clay minerals. While the loess soil, rich in illite, and the alluvial soil, rich in expansible clay minerals, bound about 40% of the added NH₄⁺ specifically, the soil derived from basalt with mainly kaolinite bound only about 10 %. From the recently “fixed” fertilizer NH₄⁺ about a half was nitrified during the incubation period of about 9 weeks. In the control there was no significant release of specifically bound NH₄⁺. Obviously this NH₄⁺ is located more deeply in the interlayers of the clay minerals and not available to microorganisms.     

Potassium Fixation and Release Characteristics of Some Benchmark Soil Series under Rice–Wheat Cropping System in the Indo‐Gangetic Plains of Northwestern India

Abstract

Potassium (K) fixation and release in soil are important issues in long‐term sustainability of a cropping system. Fixation and release behavior of potassium were studied in the surface and subsurface horizons in five benchmark soil series, viz. Dhar, Gurdaspur, Naura, Ladowal, and Nabha, under rice–wheat cropping system in the Indo‐Gangetic plains of India. Potassium fixation was noted by adding six rates of K varying from 0 to 500 mg kg^?1 soil in plastic beakers while K release characteristics were studied by repeated extractions with 1 M HNO₃ and 1 M NH₄OAc extractants. The initial status of K was satisfactory to adequate. Potassium fixation of added K increased with the rate of added K irrespective of soil mineralogy and soil depth. Soils rich in K (Ladowal and Nabha) fixed lower amounts (18–42%) of added K as compared to Gurdaspur, Dhar, and Naura (44.6–86.4%) soils low in K. The unit fertilizer requirement for unit increase in available K was more in low‐K soils. The study highlights the need for more studies on K fixation in relation to the associated minerals in a particular soil. Potassium‐release parameters such as total extractable K, total step K, and CR‐K varied widely in different soil series, indicating wide variation in the K‐supplying capacity of these soils. K released with 1 M NH₄OAc extractant was 20–33% of that obtained with 1 M HNO₃. Total extractable K using 1 M HNO₃ varied from 213 to 528 mg kg^?1 and NH₄OAc‐extractable K ranged from 71 to 312 mg kg^?1 soil in surface and subsurface layers of different soil series. The Ladowal and Nabha series showed higher rates of K release than Gurdaspur, Dhar, and Naura series, indicating their greater K‐supplying capacity.     

Effect of ammonium sulfate pretreatment on ammonia volatilization after urea fertilization

Abstract

Urea applications to soil are subject to loss by ammonia (NH₃) volatilization, unless incorporated. It has been proposed that this loss can be reduced by stimulating populations of soil nitrifiers by an ammonium sulfate [(NH₄)₂SO₄] pretreatment two to four weeks before urea application. The objective of this laboratory trial was to evaluate this concept with five diverse soils, two North American Mollisols and three South American Oxisols. The soils were incubated untreated for two weeks, followed by pretreatment with 0 or 5 kg nitrogen (N) ha^‐1 as (NH₄)₂SO₄, on a soil surface area basis. After another two weeks of incubation, the soils were treated with the equivalent of 0 or 50 kg N ha^‐1 as urea. Ammonia loss was estimated after trapping into phosphoric acid (H₃PO₄). Ammonium sulfate pretreatment reduced NH₃ loss with the two Mollisols and a sandy Oxisol and increased the recovery of the urea application as mineral [ammonium (NH₄ ⁺) + nitrate (NO₃ ^‐)] N in these soils. Little NH₃ loss was detected from the two clay Oxisols, and (NH₄)₂SO₄pretreatment did not influence NH₃ loss or recovery of urea as mineral N. An example of a cropping system where this concept may have utility is discussed.     

Effect of Organic matter application on the fate of 15N-labeled ammonium fertilizer in an upland soil

Abstract

The clay mineral composition of two “terra roxa estruturada” (TRE) soils occurring in the tropical rain forest and tropical forest/savannah transition zone, and a reddish brunizem in the savannah/semi-arid transition zone was studied comparatively in the southeast Amazon region.

Kaolin minerals were dominant in these soils, and hematite and goethite were found in the clay fraction. A small amount of 2 : 1-type clay minerals was found in two soils. The mineral composition of the clay fraction in the TRE soils was hardly influenced by the difference of the meteorological factor or their water condition in this region, and this factor should not control the influence of parent materials derived from basic rocks. The TRE soils were developed under the condition of laterite genesis, and were regarded claymineralogically as a kind of the lateritic soils.     

CLAY MINERAL DISTRIBUTION AND ORIGIN IN THE SOIL TYPES OF ISRAEL

The mineralogical composition of clays (< 2μm) in representative profiles of all soil types of Israel was investigated. The soils were classified according to their clay mineral assemblages into three groups. I. Montmorillonitic soils. Montmorillonite is the dominant mineral and exceeds 65 per cent of the total minerals found; each of the other minerals comprises less than 15 per cent. 2. Montmorillonitic-kaolinitic soils. The soil clay fractions contain 50-60 per cent montmorillonite and 15-25 per cent kaolinite, generally adding up to more than 75 per cent of the clay fraction. 3. Montmorillonitic-calcitic soils. The clays contain more than 10 per cent calcite. Montmorillonite is the dominant clay mineral (except for one soil type, mountain rendzina, where calcite is dominant). The first and second assemblages are typical of the soils of the Mediterranean zone, whereas the soils of the desert zone are characterized by the third assemblage. The origin of montmorillonite, kaolinite, and illite, the three main clay minerals, was found to be detritic, as was the origin of palygorskite which was mainly found in the calcite rich soils of the desert zone. The cation exchange capacity of montmorillonite seems to be higher under higher precipitation. Montmorillonite content and cation exchange capacity of the clays were found to be highly correlated. The carbonate content of the clay fraction and the amount of carbonate in the soil were also highly correlated.