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1.
Sorption isotherms and calcium phosphate solubility data were used to interpret the processes responsible for sorption of phosphate on three Jurassic oolitic limestones whose surface areas ranged from 1.0 to 1.5 m2/g CaCO3. It was concluded that total sorption was due to (1) an initial chemisorption reaction at final P concentrations below 0.5 μg/ml, with Langmuir adsorption parameters of about k = 10 ml/μg P and xm = 100 μg P/g; above this concentration most of the additional sorption was due to (2) phisical adsorption (of very low bonding energy) which may occur in multilayers on the initial chemisorbed layer, and (3) precipitation, probably of octacalcium phosphate, Ca8H2(PO4)6.5H2O, from solution and its deposition on the adsorbed layers. The last two reactions probably overlap and cannot be distinguished from each other.  相似文献   

2.
Effect of iron oxide on phosphate sorption by calcite and calcareous soils   总被引：3，自引：0，他引：3  
Pure calcite (AR grade CaCO3) was treated with ferrous perchlorate solution to give a surface coating of iron (Fe) oxide. Maximum sorption (xm) of phosphate (P) by the calcite increased from 18.2 to 160 mg P kg?1 as the amount of coating increased from 0.00 to 16.0 g Fe2O3, kg?1 CaCO3. Evidence for Fe oxide coatings on carbonate minerals in two Sudanese soils was obtained by optical microscopy and electron-probe microanalysis. The relative contributions of carbonate and Fe oxide minerals, and Fe oxide coatings to P sorption in these soils were calculated, based on an assumed model of oxide distribution. Separate-phase Fe oxide was the major contributor (30–40%) to P sorption in the soils; the Fe oxide coatings on carbonate minerals were only minor contributors (< 6%), and the contribution of uncoated carbonate minerals was found to be negligible (<1 %). These results suggest a very minor role for carbonate minerals, even when coated with Fe oxide, in the sorption of P by these calcareous, Sudanese soils.  相似文献   

3.
For forty-one soils (pH > 5.0) from southern England and eastern Australia, the Langmuir equation was an excellent model for describing P adsorption from solutions < 10-3M P, if it was assumed that adsorption occurs on two types of surface of contrasting bonding energies. For most of these soils, which were relatively undersaturated with P, this equation may be written as: where x = adsorption, k = adsorption/desorption equilibrium constant, xm= monolayer adsorption capacity, and c = equilibrium solution concentration. The relative magnitude of the parameters for each surface were approximately: xm= 0.3 x″m=0.3 and k′= 100 k. More than 90 per cent of the native adsorbed P occurs on the high-energy surface in most soils.  相似文献   

4.
Cd adsorption isotherms were measured on five Israeli soils ranging in specific surface area from 65 to 315m2/g. Retention capacity of Cd ranged from 4.7 × 103 to 10 × 103μg/g soil (8.4 to 17.9 mequiv/100 g soil) and was correlated with the specific surface area. Almost all the adsorbed Cd was exchangeable with 0.5 M CaCl2 and the remaining fraction was extractable in 0.5 M HCl. Plots of Kd, the distribution coefficient of Cd between the solid and solution phases, vs. Γ, the surface density of adsorbed Cd, showed that all soils behave similarly, Kd sharply diminishing with Γ. It was suggested, based on comparison with literature data on Cd adsorption on montmorillonite, that below γ s 0. 5 × 1017 ions/m2, specific adsorption mechanisms prevail whereas above it the adsorption is mainly due to electrostatic interactions and ion exchange.  相似文献   

5.
Behaviour of phosphate in iron oxide-rich, calcareous gleys of the Münchener Schotterebene Iron oxide-rich calcareous humic gleys of the Münchener Schotterebene (a calcareous gravel plain of the Isar river), induce phosphate deficiency symptoms particularly on corn. Phosphate adsorption on these soils increases with increasing Fe-oxide concentration and shows a strong slow rate component where log (P equilibrium concentration) is linearly correlated with log (time). The Fe-oxide in these soils is a goethite consisting of needles approximately 50 nm in length and 5 nm in width with a surface area of approximately 100 m2/g. On this surface ～ 2 μmol P/m2 can be adsorbed in the presence of calcite. Adsorption was measured in various electrolytes and follows the order 0.003 M CaCl2 > 0.009 M KCl > H2O.  相似文献   

6.
Abstract

The apparent recovery of applied zinc (Zn) by plants is very low in calcareous soils of Iran because most of it is retained by the soil solids. Subsamples of 24 surface soil (clay 130–530 g kg‐1; pH 7.7–8.4; electrical conductivity 0.63–3.10 dS m‐1; organic matter 6.0–22.0 g kg‐1; cation exchange capacity 8–20 cmol kg‐1; calcium carbonate (CaCO3) equivalent 180–460 g kg‐1) representing 13 soil series in three taxonomic orders were equilibrated with zinc sulphate (ZnSO4) solutions and the amount of Zn disappeared from solution after a 24‐h shaking period was taken as that adsorbed (retained) by the soil solids. The adsorption data were fitted to Freundlich (X=ACB) and Langmuir [X=(K‐bC)/(1+K#lbC)] adsorption isotherms. Backward stepwiseprocedure was used to obtain regression equations with isotherms coefficients as dependent and soil properties as independent variables. Freundlich A and Langmuir K were found to be highly significantly related to pH and clay and increasing as these soil properties increased. But Langmuir b was related only to clay and Freundlich B showed no significant relationship with any of the properties studied. The distribution coefficient (also called maximum buffering capacity), calculated as the product of Langmuir K and b, was also found to be highly significantly related to pH and clay. It is concluded that pH and clay content of calcareous soils are the most influential soil properties in retention of Zn.  相似文献   

7.
Abstract

More than 50% of the irrigated soils in the Sultanate of Oman is in the coastal plains of the Batinah area. Intensive agriculture and groundwater depletion have led to seawater intrusion and soil salinization. As a prerequisite to combat this problem, basic studies on some soil properties were done and are presented. The textural classification ranged from sand and loamy sand to fine‐textured silt loams, and the soil moisture characteristics (0.1–15 bars) revealed field capacities (0.3 bar) and permanent wilting point (15 bars) ranges of 40 to 2%, respectively. The soils are generally calcareous with about 40% calcium carbonate (CaCO3), but low in gypsum [calcium sulfate (CaSO4) content]. The EC1:5 values disclosed the extent of salinization with increasing values of up to 16 dS/m towards the coastal areas of the fine‐textured soils. This was coupled with high sodium (Na) adsorption ratios of up to 30 indicating saline‐sodic conditions.  相似文献   

8.
Phosphate sorption by calcareous soils has been studied mainly on heavily fertilized agricultural soils and soils with calcite as the main carbonate mineral. We examined factors affecting phosphate adsorption in the soils of a semi-arid, mediterranean, dolomitic, soil and vegetation chrono-sequence in southeastern Spain. The youngest soils are highly eroded, Sandy Regosols (Typic Xerorthents) under gorse-scrubland vegetation. These have small P sorption capacities, large Mg-Ca carbonate contents but small amounts of Fe and Al oxides. Small total P (HNO3/HClO4 digestion) concentrations (30–130 μg P g?1), of which up to 90% is Ca-bound (HCl-extractable), are typical of these young soils. P sorption markedly increased when Ca2+ was added to the solution. The fractionation of previously sorbed P indicates that the fate of most of this extra-sorbed P is the labile-P fraction sorbed on to (carbonate) surfaces and the apatite-like fraction (NaHCO3-extractable and HCl-extractable fractions). At the other extreme, older more-intensively weathered, sandy-clay-loam rendzinas (Entic Haploxerolls), supporting dense mature garrigue, have a much greater P adsorption capacity and larger clay and Fe and Al oxide concentrations. They have more total P (ca 400 μg P g?1), much of it in occluded form (residual fraction). These soils show no significant differences in P sorption whether or not CaCl2 was used as a background electrolyte. Considering the overall variations within the chronosequence, dithionite extractable Fe and Al are the properties best correlated with P sorption. This support the general finding that crystalline Fe-oxides (e.g. goethite and haematite) appear to be the most important P-sorbing component for soils in the Mediterranean region, rather than amorphous Fe-oxides (e.g. ferrihydrite) as is reported for more mesic areas. Stepwise multiple regression and fractionation data, however, suggest that, provided the soil solution is rich in Ca2+, carbonate may also be a significant contributing factor to P sorption, especially in the youngest of these dolomitic soils.  相似文献   

9.
ABSTRACT

We studied (i) the pH buffer capacity (pHBC) of calcareous soils varied widely in calcite and texture, (ii) the contribution of soil properties to pHBC and (iii) the significance of using a model based on calcite dissolution to estimate the pHBC of calcareous soils. The pHBC of soils was measured by adding several rates of HCl to soils (100–6500 mM H+ kg–1), in a 0.01 M CaCl2 background and an equilibration time of 24 h. The pHBC (mM H+ kg–1 pH?1) varied from 55 to 3383, with the mean of 1073. The pHBC of the soils was strongly correlated with soil CaCO3 equivalent (calcite) (r = 0.94), sand (r = ?0.72), silt (r = 0.60), EC (r = 0.63), pH (r = 0.55), and weakly (r = 0.37) but significantly with clay content. The attained pHBC values indicated that calcite was probably the main buffer system in these soils. The chemical equilibrium model successfully predicted pH titration curves based on calcite dissolution, indicating buffering of acid inputs in the calcareous soils is dominated by calcite dissolution. The model can be used to simulate acidification of calcareous soils and to provide information for making environmental management decisions.  相似文献   

10.
宁夏灌淤土对磷吸附的初步研究   总被引：8，自引：0，他引：8  
何文寿 《土壤学报》1992,29(2):142-149
本文报道了宁夏灌淤土12个代表性土样对磷的等温吸附与解吸特性。实测吸附曲线与Preundlich、Langmuir和Temkin三种等温吸附方程都很吻合。全部供试样品的相关系数变化在0.931-0.999之间,均达极显著水平(p<0.01)。其中Langmuir等温式与本实验资料最为吻合。供试土壤对磷的最大吸附量(Xm)变化在172-460μgP/g之间,平均为347±28μgP/g。影响其大小的因子主要是物理性粘粒和CaCO3,含量,均达极显著正相关。灌淤土不同土层的吸磷量大小依次为:剖面24>23>21>22,而解吸磷能力大小依次为:剖面23>22>21>24。磷的解吸量与吸附量之间呈极显著正相关。根据本试验数据,土壤对磷的等温吸附曲线可以用来预测土壤需磷量。  相似文献   

11.
In the present study, Olsen [0.5 M sodium bicarbonate (NaHCO3), pH 8.5] and resin–bicarbonate (HCO3) tests underestimated available phosphorus (P) in calcareous soils treated with gypsum (CaSO4). The reaction of CaSO4 and HCO3 ? ion or resin–HCO3 to form calcium carbonate (CaCO3) precipitate reduced the strength of the Olsen NaHCO3 extractant and resin–HCO3 strip for P extraction. The iron (Fe) oxide–impregnated filter paper (Pi strip) was independent of CaSO4 influence and thus correctly estimated soil‐available P with respect to plant response to soil‐available P. Two greenhouse experiments were conducted with maize and wheat grown on calcareous soils treated with different rates of CaSO4. The results confirmed that Olsen and resin–HCO3 tests should not be used to measure available P or labile P in the P fractionation scheme in the calcareous soils containing significant amounts of gypsum.  相似文献   

12.
Abstract

The multiple‐element extractant Mehlich 3 (M3) has not been tested extensively in Europe. In this Land, soil‐P test recommendations are based, since decades, on the evaluation of the Olsen‐extractable P, and the optimal soil‐P levels have been established to range between 1.5 and 3.0 mg of Olsen‐P per 100 g of soil. A research programme was started in order to assess the suitability of M3 as routine soil‐P test in European laboratories. As a first approach, we develop conversion equations from Olsen‐P to M3‐P, in order to assess the agreement and the consistency of the measurements under a wide range of chemical and physical soil properties. To this aim, 120 samples with drastically contrasting features were selected within 206 soils collected from all the regions of South Italy. Soil‐P ranges were 0.07–60.53 for M3, and 0.08–21.47 mg/100 g for Olsen. The results showed that M3‐P was a P extractant more efficient than Olsen. The amounts of M3‐P were, on the average, twice as large as the Olsen‐P ones, with mean values of 5.70 and 2.75 mg/100g, respectively. The soil properties exerted a great influence, as well as showed a contrasting effect, on the extraction efficiency of each method. For neutral‐alkaline calcareous soils, the average M3‐P/Olsen‐P ratio increased to 2.52, and the efficiency of M3 poorly varied according to soil pH and CaCO3 content. On the contrary, in CaCO3‐free acidic soils, the M3‐P/Olsen‐P ratio decreased to 1.63. In particular, anomalous ratio values less than 1.0 were observed for acidic soils with high content of organo‐mineral complexes with be shifted to 3.7–7.7 for calcareous soils, and to 2.7–4.9 for CaCO3‐free soils. Field calibrations would give more information to establish the proper values according to either the soil properties and plant requirements. The results encourage the introduction of M3 as routine soil‐P test in our Countries. One must take into account, however, that some soil properties, in particular the CaCO3 content, migth be considered for a more precise comparative evaluation with existing laboratory data.  相似文献   

13.
Saline–sodic and sodic soils are characterized by the occurrence of sodium (Na+) to levels that can adversely affect several soil properties and growth of most crops. As a potential substitute of cost‐intensive chemical amelioration, phytoremediation of such soils has emerged as an efficient and low‐cost strategy. This plant‐assisted amelioration involves cultivation of certain plant species that can withstand ambient soil salinity and sodicity levels. It relies on enhanced dissolution of native calcite within the root zone to provide adequate Ca2+ for the Na+ Ca2+ exchange at the cation exchange sites. There is a lack of information for the Na+ balance in terms of removal from saline–sodic soils through plant uptake and leaching during the phytoremediation process. We carried out a lysimeter experiment on a calcareous saline–sodic soil [pH of saturated soil paste (pHs) = 7.2, electrical conductivity of the saturated paste extract (ECe) = 4.9 dS m−1, sodium adsorption ratio (SAR) = 15.9, CaCO3 = 50 g kg−1]. There were three treatments: (1) control (without application of a chemical amendment or crop cultivation), (2) soil application of gypsum according to the gypsum requirement of the soil and (3) planting of alfalfa (Medicago sativa L.) as a phytoremediation crop. The efficiency of treatments for soluble salt and Na+ removal from the soil was in the order: gypsum ≈ alfalfa > control. In the phytoremediation treatment, the amount of Na+ removed from the soil through leaching was found to be the principal cause of reduction in salinity and sodicity. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

14.
An explanation is put forward for the shape of adsorption envelopes found for phosphate adsorption by various metallic oxides. The equation xm= C1 (μH3PO4+μ∑anions) is proposed, where μH3pO4 is the chemical potential of undissociated H3PO4; μ∑anions is the chemical potential of all phosphate anions considered as one. component; C1 is a constant that includes influences of surface charge, chemical affinity of the metal for phosphate, specific surface area, etc., and xmis the calculated Langmuir maximum adsorption of P at each pH. The dependence of C1 on the metal present in the oxide is shown.  相似文献   

15.
Characterization of calcium phosphates depended upon the nature and the amount of phosphate used to react with reagent-grade CaCO3. Formation of octa-calcium phosphate (OCP) was inferred from the solubility equilibria after reacting CaCO3 with KH2PO4 solutions. Isotopic exchange measurements confirmed the presence of OCP, when the amount of P retained exceeded 44 μrnoles/g CaCO3. The determined surface-Ca to surface-P molar ratios were close to the theoretical Ca/P ratio of 1.33 in OCP. As P retained on CaCO3 decreased the surface Ca/P ratio markedly increased because of interference from surface Ca of the CaCO3. When CaCO3 was reacted with monocalcium phosphate (MCP), solubility equilibria indicated the formation of dicalcium phosphate dihydrate (DCPD). Isotopic exchange measurements, however, showed an average Ca/P ratio of only 0.375. This value corresponds to the composition of the metastable triple point solution (MTPS) formed on MCP dissolution rather than to the Ca/P ratio in DCPD. MCP application decreased the measured surface-Ca (exchangeable Ca) either for soil or Ca-resin, because of blocking of the exchange sites by the MCP reaction products and, consequently, a lower rate of isotopic exchange. Surface phosphorus of the two investigated calcareous soils proved to be proportional to the lowering in pH initiated by MCP application. Characterization of MCP reaction products in calcareous soils may thus prove infeasible, in view of the unexpected reduction in surface-Ca and the pH dependency of surface P.  相似文献   

16.
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17.
土壤对磷的吸附与解吸及需磷量探讨   总被引：5，自引：0，他引：5  
本文探讨了不同质地土壤对磷的吸附与解吸。根据Langmuir方程式求出不同土壤对磷的最大吸附量。影响磷吸附的土壤理化性质主要为粘粒含量、碳酸盐含量和有效磷含量。以Freundhich方程式X=acb中的c值为每克土中含P0.2μg时而计算出的X量可做为施磷量的依据。  相似文献   

18.
Summary

A simple, single‐step extraction with LiEDTA for the estimation of CEC and exchangeable bases in soils has been developed. Multivalent cations are stripped from the soil adsorption sites by the strongly chelating agent EDTA, and are replaced by Li. In soils without CaCO3 or water soluble salts, exchangeable divalent cations (Ca, Mg) are chelated by EDTA and exchangeable monovalent cations (Na, K) are replaced in a single extraction step using 0.25–2.5 g of soil and 10.0 ml of extractant.

In calcareous soils the CEC can be determined in the same way, but for the extraction of exchangeable Ca and Mg, another separate extraction is needed because dissolution of calcite by EDTA is unavoidable. This extraction is done with as much NaEDTA as needed to extract only exchangeable Ca and Mg in a 1:2 (m/V) soil/alkaline‐50% (V/V) aethanolic solution to minimize dissolution of calcite.

In gypsiferous soils gypsum is transformed into insoluble BaSO4 and soluble CaEDTA by LiBaEDTA thus avoiding interference of Ca from dissolution of gypsum, which renders the traditional methods for determining CEC unsuitable for such soils. To determine exchangeable Ca and Mg, Na4EDTA is used as for calcareous soils.

In saline/sodic soils replacement of Na by Li is incomplete but the Na/Li‐ratio at the complex after extraction is proportional to the molar Na/Li‐ratio in the extracts, so that the CEC and original exchangeable sodium (ESP) content can be calculated. Additional analysis of Cl and, if necessary, SO4 in the extracts of saline soils can be used to correct for the effect of dissolution of the salts on the sum of exchangeable cations.

This new method is as convenient as the recently developed AgTU (silverthiourea), but is better suitable for calcareous and gypsiferous soils.  相似文献   

19.
ABSTRACT

During the 2017 and 2018 seasons, two field experiments were conducted on newly reclaimed saline calcareous soil (7.13 dS m?1, 16.9% CaCO3) in the experimental farm of the Faculty of Agriculture, Demo, Fayoum Governorate, Egypt. The current work aimed at identifying the potential positive effects of applied humic acid (HA) and elemental sulfur (S) on some soil properties and barley plant performance. The results showed that the application of HA and/or S at different rates ameliorated the adverse effects of saline calcareous soil conditions and significantly reduced some chemical properties of the soil (e.g., pH, ECe, and CaCO3%), while soil organic matter (OM%) and some nutrients (e.g., P, Fe, Mn, Cu, and Zn) contents were significantly increased. In addition, the contents of nutrients (e.g., P, Fe, Mn, Cu, and Zn) in barley plant and yielded grain, grain content of N and protein (%), and the performance (e.g., plant height, spike length, grain and straw yields, and weight of 1000-grain) of barley plant were significantly increased with the application of HA and/or S. The best results were obtained through the integrative application of 100 kg HA + 400 kg S ha?1 to the tested saline calcareous soil. Therefore, the integrative soil application of 100 kg HA + 400 kg S ha?1 can be recommended for the cultivation and sustainability of crop production in saline calcareous soil, in addition to rationalize the use of mineral fertilizers, which represent a surplus point for the sustainable agriculture system.  相似文献   

20.
Sixteen soils and 4 soil preparations were cropped exhaustively with ryegrass in the glasshouse and monocalcium phosphate potentials (½pCa+pH2PO4=1) were measured after each of 6 consecutive harvests. The amounts of phosphorus (Q) removed from the soils by ryegrass accounted for 95·1–96·6 per cent of the variance in 1 for 3 soils and 2 soil preparations (P < 0·001), for 88·4–93·7 Per cent of the variance for 6 soils and 2 soil preparations (0·001 < P < 0·01), for 71·6–82·6 per cent of the variance for 3 soils (0·01 < P < 0·05) and for insignificant amounts of the variance for 4 soils. Values of ΔI/ΔQ ranged from 7 × 10–4 to 431 × 10–4½pCa+pH2PO4/ppm P removed from soil. ΔI/ΔQ tended to decrease (i.e. the soils were more buffered) with increasing clay contents and with increasing amounts of NaHCO3-soluble P and to increase (i.e. the soils were less buffered) with increasing amounts of CaCO3. Variations in organic C did not significantly affect ΔI/ΔQ. The following equation accounts for 81 per cent of the variance in ΔI/ΔQ for all soils except those in equilibrium with octacalcium phosphate: ΔI/ΔQ× (104) = 225·9–4·17(% clay)+8·01(% CaCO3)–1·38(ppm NaHCO3-soluble P).  相似文献   

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