Accumulation of Lead and Arsenic by Potato Grown on Lead–Arsenate-Contaminated Orchard Soils

There are concerns of potential food chain transfer of metals in crops grown on lead–arsenate-contaminated soils. The objective of this study was to investigate lead and arsenic uptake by four potato (Solanum tuberosum L.) cultivars grown on lead–arsenate-contaminated soils with lead and arsenic concentrations ranging from 350 to 961 and 43 to 290 mg kg^?1, respectively. Yield was not reduced due to treatment. Potato tubers were washed thoroughly before peeling. Lead concentration in both peeled tubers and peel was below instrument detection limit. Arsenic concentration in peeled tubers grown on the lead–arsenate soils ranged from 0.24 to 1.44 mg kg^?1. Arsenic concentration was 60% higher in the peel than in the peeled tuber. The relatively high arsenic levels in the peel demonstrated that arsenic was taken up into the potato peel tissue. It is recommended that if potatoes are grown on these soils they should be peeled before consumption.

Abbreviations Pb, lead; As, arsenic; DW, dry weight; FW, fresh weight     

Effect of Submergence on Iron Transformation and Phosphorus Availability in Calcareous Soils

A thermostatic incubation experiment was carried out to estimate the effects of flooding periods,stalk application and P addition of Fe transformation and P availability in calcareous soils.Submergence increased amorphous Fe,especially in the case of stalk application.The newly formed amorphous Fe with a great surface area played an important role in Psorption;and submergence also stimulated the dissolution of inorganic P,thus increasing the availability of soil P in calcareous soils.Meanwhile,a part of soluble P was absorbed and fixed again on the surface of newly formed amorphous Fe,thus resulting in a decrease of P availability.Soil rapidly available P increased after 150-day incubation.There existed significantly negative correlations between soil amorphous Fe content and soil Fe-P and rapidly available P contents.Submerged conditions promoted the transformation of inorganic P added toward Fe-P in calcareous soils,especially in the case of stalk application.     

Effect of Flooding Lead Arsenate–Contaminated Orchard Soil on Growth and Arsenic and Lead Accumulation in Rice

Lead arsenate has been used as pesticide. Flooding soils contaminated by lead arsenate could increase plant arsenic and lead and become a human health risk. The objective was to determine the effects of flooding of lead‐arsenate soils on rice grain yield and arsenic and lead accumulation. Bagstown and Chashmont soils with high levels of arsenic and lead were planted with rice in the greenhouse under flooded and nonflooded conditions. Flooding reduced grain yield and increased grain arsenic concentration on both soils. Grain lead decreased with flooding for the Bagstown soil but increased for the Chashmont. Arsenic and lead concentrations in the straw were more than in grain. Grain arsenic and lead levels observed would not be expected to become a human health risk. However, bioavailability studies are needed. The high arsenic and lead in the straw may indirectly become a human health risk because rice straw is used for livestock feed and bedding.     

Modified Soil‐Test Methods for Extractable Phosphorus in Acidic,Neutral, and Alkaline Soils

Abstract

Although numerous soil‐test methods for estimating extractable phosphorus (P) have been developed around the world, their results are difficult to compare because of the very different scale levels used. In the present study, the Bray–Kurtz method (Bray‐P) is used as a reference value. Two other methods [lactate‐P and sodium bicarbonate (NaHCO₃)‐P] were modified to facilitate the comparison of extractable‐P determinations, mainly by adjusting the shaking time. These three methods were applied to 101 soil samples from an extensive region of Argentina with soil pH values ranging from 5.5 to 8.5. The results confirm that the Bray‐P and the two modified methods (lactate‐P and NaHCO₃‐P) determine similar contents of extractable P but are not applicable to all types of soils and conditions. Equations that minimize the statistical error were selected for soil properties such as organic carbon (OC) content, pH, soluble salts, and calcium carbonate content. Correlation coefficients between Bray‐P and NaHCO₃‐P increased to 0.91 and 0.95 in soils with high and low OC levels, respectively. It was also demonstrated that the lactate‐P test is not suitable for soils rich in calcium carbonate or soluble salts. These two modified methods are expected to be useful for testing P values that impact agricultural production.     

Effect of Organic Matter and Salinity on Ethylenediaminetetraacetic Acid–Extractable and Solution Species of Cadmium and Lead in Three Agricultural Soils

Abstract

A study was conducted to investigate the chemical speciation of added cadmium (Cd) and lead (Pb) and their availability as influenced by fresh organic matter (OM) and sodium chloride (NaCl) in three agricultural soils. The soils were treated with 20 mg Cd/kg as cadmium nitrate [Cd(NO₃)₂ · 4H₂O], 150 mg Pb/kg as lead nitrate [Pb(NO₃)₂], 20 g/kg alfalfa powder, and 50 mmol/kg of NaCl and then incubated for 3 months at 60% water‐holding capacity (WHC) and constant temperature (25 °C). Subsamples were taken after 1, 3, 6, and 12 weeks of incubation, and electrical conductivity (EC), pH, dissolved organic carbon (DOC), and concentrations of cations and anions were determined in the 1:2.5 soil/water extract. Available Cd and Pb were determined in 0.05 M ethylenediaminetetraacetic acid (EDTA) extract. Concentrations of organic and inorganic species of Cd and Pb in soil solution were also predicted using Visual Minteq speciation program. The most prevalent species of dissolved Pb and Cd in the soils were Pb‐DOC and Cd²⁺ species, respectively. Salinity application increased the available and soluble Cd significantly in the acid and calcareous soils. It, however, had little effect on soluble Pb and no effect on available Pb. Organic‐matter application decreased availability of added Pb significantly in all soils. In contrast, it raised soluble Pb in all soils except for the acid one and approximated gradually to the added Pb with time. Impact of OM on available Cd was somewhat similar to that of Pb. Soluble Cd increased by OM application in the calcareous soil, whereas it decreased initially and then increased with time in the other soils.     

Residual Effect of Phosphorus Fertilizer in a Low‐Humic Andosol with Low Extractable Phosphorus

Abstract

Phosphorus (P) fertilization is quite important for crop production grown on Andosols. Fertilizer P‐use efficiency was 17% in a long‐term wheat experiment on a low‐humic Andosol. Residual effects of P fertilization were investigated using field soils in pot experiments. Topsoil was collected from the plots with or without annual P fertilizer at the rate of 65 kg‐P ha^?1 for 23 years (nitrogen phosphorous potassium (NPK) soil and nitrogen potassium (NK) soil, respectively). There was no significant difference in dry matter of wheat and P uptake between NPK and NK soils. However, dry matter of rice and P uptake were higher in NPK soil than in NK soil. Inorganic aluminum P (Al‐P_i) and iron P (Fe‐P_i) increased in NPK soil. Increase in Al‐P_i and Fe‐P_i during 23 years contributed little to P uptake by wheat, and repeated P fertilization is indispensable to obtain acceptable grain yield.     

Evaluating the Influence of Storage Time,Sample‐handling Method,and Filter Paper on the Measurement of Water‐Extractable Phosphorus in Animal Manures

Abstract

Surface‐applied manures create a potential phosphorus (P) runoff hazard, especially when unincorporated. In such cases, the concentration of water‐extractable P in the manure has been correlated to soluble P concentrations in runoff. This study evaluated the influence of holding time, sample‐handling procedure, and filtration method on measurement of the water‐extractable P content of manures in a 3×3×2 factorial arrangement of treatments. A two‐way interaction between holding time and sample‐handling procedure occurred for most samples. Six samples had water‐extractable P concentrations that were less than or equal to dried and dried/ground treatments. Only one sample had higher water‐extractable P concentrations for fresh than for dried and dried/ground treatments. When significant differences occurred as a result of the filtration method, results for Whatman No. 40 filters, with a larger pore size than 0.45 µm nitrocellulose membranes, were usually higher. There was no significant difference in the coefficient of variation across sample‐handling procedures, suggesting that efforts to dry and/or grind samples were not needed. These results support the adoption of a standardized protocol for measuring water‐extractable P in manures that represents the appropriate balance between the ease of implementation and the strength of the correlation to P runoff concentrations.     

Effect of Olive‐Derived Organic Amendments on Lead,Zinc, and Biochemical Parameters of an Artificially Contaminated Soil

Abstract

An incubation experiment was conducted to ascertain the effects of three olive‐derived organic amendments (fresh, compost, and vermicompost olive cake) on the soluble and diethylenetriamine pentaacetic acid (DTPA)–extractable lead (Pb) and zinc (Zn) and on different enzymatic activities in an artificially contaminated calcareous soil. Application of the compost and vermicompost, which increased amounts of humic acids in soil, initially stimulated dehydrogenase, ß‐glucosidase, and urease activities, which tended to decline afterward. In contrast, dehydrogenase and ß‐glucosidase activities were lower after application of the fresh olive cake. Amounts of soluble Pb and Zn increased when fresh olive cake was added to the soil, due to the high content of water‐soluble carbon in this amendment. On the contrary, application of the compost and vermicompost decreased the concentration of soluble Zn and did not change the soluble Pb levels in the soil. The DTPA‐Pb and DTPA‐Zn were scarcely affected by the application of the three olive‐derived amendments.     

Short‐Term Effect of Targeted Placements of Sheep Excrement on Grassland in Inner Mongolia on Soil and Plant Parameters

Abstract

Grazing animal excrement plays an important role in nutrient cycling and redistribution in grazing ecosystems, due to grazing in large areas and return in small areas. To elucidate the changes to the soil and pasture caused by sheep urine, fresh dung, and compost patches, a short‐term field experiment using artificially placed pats was set up in the autumn of 2003 in the Inner Mongolian steppe. Urine application significantly increased soil pH during the first 32 days in soil layers at depths of both 0–5 cm and 5–15 cm. Rapid hydrolysis of urea gave large amounts of urine‐nitrogen (N) as ammonium (NH₄ ⁺) in soil extracts and was followed by apparent nitrification from day 2. Higher inorganic N content in the urine‐treated soil was found throughout the experiment compared with the control. No significant effects of sheep excrement on soil microbial carbon (C) and soil microbial N was found, but microbial activities significantly increased compared with the control after application of sheep excrement. Forty‐six percent of dung‐N and 27% of compost‐N were transferred into vegetation after the experiment. The results from this study suggest that large amounts of nutrients have been lost from the returned excrement patches in the degraded grassland of Inner Mongolia, especially from sheep urine‐N.     

Uptake,Translocation, and Transformation of Arsenic by Four Fern Species in Arsenic‐Spiked Soils

Arsenic (As) toxicity has become a global concern because of the ever‐increasing contamination of water, soil, and crops in many regions of the world. Although most plants are susceptible to As, some ferns are resistant to it and can accumulate As. In this study, four species of ferns, Asplenium nidus (AN), Pteris umbrosia (PU), Polypodium vulgare (PV), and Pteris cretica (PC), were screened for their ability to tolerate and hyperaccumulate As. Ferns were exposed to 120 mg As kg^?1 as sodium arsenate (Na₂HAsO₄) for 50 days under natural sunlight in greenhouse conditions, and the fronds and roots were analyzed for As speciation and selected macronutrients [potassium (K) and phosphorus (P)]. The species of ferns varied widely in their abilities to transport As to the fronds (ranged from 164 to 4820 mg kg^?1 DW) with the greatest frond As concentration found in PU (4820 mg kg^?1). The distribution of soil As fractions indicated that As was mostly bound carbonate (carb) (32.4%) and in the residual fractions (45.1%). Chemical fractionation of As‐spiked soil indicated that the greatest reduction in soil As after growing was in carb As form. Arsenic speciation analysis shows that >82% of the total As in the aboveground biomass is present as the reduced form of As, arsenite [As(III)], which is considered to be the more toxic form. However, in roots, only 60% of the As is present as As(III). Furthermore, among the four species of ferns, PU is the most promising to be used in the remediation of the affected area. Therefore, it is possible to use PU to remediate As‐contaminated soils by repeatedly harvesting its fronds.     

Distribution of Total and DTPA‐Extractable Zinc,Copper, Manganese,and Iron in Vertisols of India

Abstract

Vertisols of India are developed over isohyets of 600 to 1500 mm, and their chemical cycles are set by drainage, landforms, and particle size, which results in variable pedogenic development within the otherwise homogeneous soils. The purpose of this study was to identify pedogenic processes in the distribution of total and DTPA‐extractable zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe). The soils are developed over basaltic parent material of Cretaceous age. Soil samples were drawn from genetic horizons of the 13 benchmark profiles and analyzed by using HF–HClO₄ acid for total and DTPA extraction. Correlation coefficients were calculated taking all samples together. The total concentration varied from 24 to 102 mg kg^?1 for Zn, 21 to 148 mg kg^?1 for Cu, 387 to 1396 mg kg^?1 for Mn, and 2.36 to 9.50% for Fe. Their variability was proisotropic and haplodized, and their concentrations increased with advancing isohyets. Within the isohyets, hindrance in drainage caused retention of Zn and Cu but loss of Fe. The piedmont soils had more Fe than alluvium soils. The spatial distribution of total contents of Zn, Cu, and Fe was influenced by the pedogenic processes associated with Haplusterts but not with provenance materials. Surface concentrations of the elements by biotic lifting and/or harvest removal were negated by the pedoturbation that further contributed to the irregular distribution of the elements in the profiles. Total Zn and total Cu had positive coefficients of correlations with coarse clay, whereas total Mn and total Fe were positively correlated with fine clay. The DTPA‐extractable forms were functions of isohyets and drainage and showed association with organic carbon content and coarse clay.     

Effects of Arsenic‐Contaminated Irrigation Water on Growth,Yield, and Nutrient Concentration in Rice

Abstract

A study was undertaken to determine the effects of different concentrations of arsenic (As) in irrigation water on Boro (dry‐season) rice (Oryza sativa) and their residual effects on the following Aman (wet‐season) rice. There were six treatments, with 0, 0.1, 0.25, 0.5, 1, and 2 mg As L^?1 applied as disodium hydrogen arsenate. All the growth and yield parameters of Boro rice responded positively at lower concentrations of up to 0.25 mg As L^?1 in irrigation water but decreased sharply at concentrations more than 0.5 mg As L^?1. Arsenic concentrations in grain and straw of Boro rice increased significantly with increasing concentration of As in irrigation water. The grain As concentration was in the range of 0.25 to 0.97 µg g^?1 and its concentration in rice straw varied from 2.4 to 9.6 µg g^?1 over the treatments. Residual As from previous Boro rice showed a very similar pattern in the following Aman rice, although As concentration in Aman rice grain and straw over the treatments was almost half of the As levels in Boro rice grain. Arsenic concentrations in both grain and straw of Boro and Aman rice were found to correlate with iron and be antagonistic with phosphorus.     

Cadmium,Nickel, Chromium,and Lead Levels in Soils and Vegetables under Long‐Term Irrigation with Industrial Wastewater

Abstract: The industrial activity areas, rivers, and water sources in neighboring areas are influenced by wastewater of manufacturers. Utilizing water influenced by wastewater increased heavy metals in soils and plants. In 2004, to investigate the effects of wastewater on cadmium (Cd), nickel (Ni), chromium (Cr), and lead (Pb) content in soil and plants, wastewaters of three manufactures (chrome chemical, wood and paper, and textiles) were examined. At harvest time roots, whole shoots (rice, spinach, clover, grass), and rice grain in industrial wastewater–influenced areas and uninfluenced areas were sampled. Soil samples were also taken (0–15, 15–30 cm). Results indicated that when wastewater was discharged into the river water, the concentrations of Cd, Ni, Cr, and Pb increased in river water. Application of river water influenced by industrial wastewater for irrigation of rice and another plants enhanced, the amounts of available Cd, Ni, Cr and Pb in soil. In subsurface horizons (15–30 cm), the concentrations of heavy metals were more than in the surface horizon (0–15 cm). With increasing cation exchange capacity in the soil, the amount of available Cr increased. When the calcium carbonate content in soils was raised, the available Cd and Pb increased in the soil, but Ni and Cr decreased. Meanwhile, organic matter enhanced the concentrations of heavy metals in soil. Accumulations of heavy metals were higher in the roots of rice (control and treatment) than in shoot and rice grain. Cadmium accumulation in rice root was three times that in whole shoot, and grain was two times more than control. The concentrations of Ni, Cr, and Pb in root, whole shoot, and grain of rice were two times higher in industrial wastewater–treated areas. The concentrations of heavy metals in root and whole shoot of spinach, clover, and grass in industrial wastewater area increased about 100%, but not to a toxic level. Cadmium translocated more than other heavy metals from soil to root, whole shoot, and grain of rice, and whole shoot of spinach, clover, and grass.     

Drinking‐Water Treatment Residual Effects on the Phosphorus Status of Field Soils Amended with Biosolids,Manure, and Fertilizer

Abstract

Concerns about surface water pollution with phosphorus (P) from biosolids and manures are prompting land application guidelines that limit residual application rates to those based on crop‐P removals (typically, no more than 2 Mg ha^?1). Such rates are so low that the beneficial recycling of residuals is seriously threatened. Greater application rates [i.e., nitrogen (N) based] require judicious selection of residuals (low soluble P contents) and/or soil amendments, such as drinking‐water treatment residuals (WTRs) to control soluble P concentration. Although in the short term, WTR is effective in reducing soluble P levels, field studies to evaluate the stability of WTR‐immobilized P are scarce. The initial objective of this study was to determine the effects of WTR on P losses to surface and groundwater from Florida sand amended with different P sources (biosolids, manure, and inorganic fertilizer) applied at P‐ and N‐based rates. However, this objective could not be pursued to its logical conclusion because of severe flooding of the field 17 months after amendment application. The flooding appears to have compromised the treatments (moved soil and associated amendments across plots), which forced early termination of the experiment. Measurements taken after the flooding, however, provided a unique opportunity to assess the usefulness of WTR in controlling P solubility following severe flooding of WTR‐amended plots. Soluble P values measured from WTR‐amended A horizon plots were significantly lower than the plots without WTR amendment throughout the study. Phosphorus‐specific measurements in the Bh horizon suggest that excessive P leaching apparently occurred in the plots without WTR amendment and the control plots, whereas very little or no P leaching occurred in the WTR‐amended plots. Thus, despite extensive hurricane‐induced flooding of the fields, the WTR was able immobilize P and prevent excessive P leaching. We conclude that WTR could reduce offsite P transport, which will lower P loads into nutrient‐sensitive surface water systems, and that WTR‐immobilized P is stable even under severe flooding conditions.     

Estimating Soil Carbon,Nitrogen, and Phosphorus Mineralization from Short‐Term Carbon Dioxide Respiration

The measurement of soil carbon dioxide (CO₂) respiration is a means to gauge biological soil fertility. Test methods for respiration employed in the laboratory vary somewhat, and to date the equipment and labor required have limited more widespread adoption of such methodologies. A new method to measure soil respiration was tested along with the traditional alkali trap and titration method. The new method involves the Solvita gel system, which was originally designed for CO₂ respiration from compost but has been applied in this research to soils with treatments of increasing dairy manure compost. The objectives of this research are to (1) examine the relationship between the CO₂ release after 1 day of incubation from soils amended with dairy manure compost that have been dried and rewetted as determined using the titration method and the Solvita gel system, and (2) compare water‐soluble organic nitrogen (N), as well as carbon (C), N, and phosphorus (P) mineralization after 28 days of incubation with 1‐day CO₂ release from the titration method and Solvita gel system. One‐day CO₂ from both titration and the Solvita gel system were highly correlated with cumulative 28‐day CO₂ as well as the basal rate from 7–28 days of incubation. Both methods were also highly correlated with 28‐day N and P mineralization as well as the initial water‐extractable organic N and C concentration.

The data suggest that the Solvita gel system for soil CO₂ analysis could be a simple and easily used method to quantify soil microbial activity and possibly provide an estimate of potential mineralizable N and P. Once standardized soil sampling and laboratory analysis protocols are established, the Solvita method could be easily adapted to commercial soil testing laboratories as an index of soil microbial activity.     

Influence of Long‐Term Sodic‐Water Irrigation,Gypsum, and Organic Amendments on Soil Properties and Nitrogen Mineralization Kinetics under Rice–Wheat System

Abstract

Influence of long‐term sodic‐water (SW) irrigation with or without gypsum and organic amendments [green manure (GM), farmyard manure (FYM), and rice straw (RS)] on soil properties and nitrogen (N) mineralization kinetics was studied after 12 years of rice–wheat cropping in a sandy loam soil in northwest India. Long‐term SW irrigation increased soil pH, exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR) and decreased organic carbon (OC) and total N content. On the other hand, application of gypsum and organic amendments resulted in significant improvement in all these soil properties. Mineralization of soil N ranged from 54 to 111 mg N kg^?1 soil in different treatments. Irrigation with SW depressed N mineralization. In SW‐irrigated plots, two flushes of N mineralization were observed; the first during 0 to 7 d and the second after 28 d. Amending SW irrigated plots with GM and FYM enhanced mineralization of soil N. Gypsum application along with SW irrigation reduced cumulative N mineralization at 56 days in RS‐amended plots but increased it under GM‐treated, FYM‐treated, or unamended plots. Nitrogen mineralization potential (N_o) ranged from 62 to 543 mg N kg^?1 soil. In the first‐order zero‐order model (FOZO), the easily decomposable fraction ranged from 5.4 to 42 mg N kg^?1 soil. Compared to the first‐order single compartment model, the FOZO model could better explain the variations in N mineralization in different treatments. Variations in N_o were influenced more by changes in pH, SAR, and ESP induced by long‐term SW irrigations and amendments rather than by soil OC.     

Interrelation of Inorganic Phosphorus Fractions and Sorghum‐Available Phosphorus in Calcareous Soils of Southern Khorasan

The objectives of this research were to determine inorganic phosphorus (P) fractions in calcareous soils of southern Khorasan and find their relationship with sorghum‐available P. Eighty soil samples were obtained and analyzed for some physical and chemical characteristics, among them 24 samples that varied in plant‐available P and soil properties were used for soil testing. From 24, 8 samples were selected for P fractionation as well. Five extraction procedures were used for soil testing. Results indicate that the extracted plant‐available P by the Olsen et al. (1954 Olsen, S. R., Cole, C. V., Watanabe, F. S. and Dean, L. A. 1954. Estimation of available phosphorus in soils by extraction with sodium bicarbonate (USDA Circ. 939), Washington, D.C.: U.S. Government Printing Office.  [Google Scholar]) and Paauw (1971 Paauw, F. V. 1971. An effective water extraction method for the determination of plant available phosphorus.. Plant and Soil, 34: 497–481.  [Google Scholar]) methods show the greatest correlation coefficients with plant P uptake and sorghum dry matter. The sequential inorganic P extraction analyzing indicated that the abundance of various inorganic fractions was in the order Ca₁₀‐P > Al‐P > Ca₈‐P > Ca₂‐P > Oc‐P > Fe‐P. The results also indicate Olsen P correlates positively and significantly with Ca₂‐P and Fe‐P fractions and positively but not significantly with the Al‐P fraction.     

Heavy‐Metal Concentration of Sewage‐Contaminated Water and Its Impact on Underground Water,Soil, and Crop Plants in Alluvial Soils of Northwestern India

Abstract

Heavy‐metal concentration in underground and surface water, soil, and crop plants growing in farmers' fields near the industrial city of Ludhiana, Punjab, India, that receive irrigation with water contaminated with sewer and untreated industrial effluents was studied. The concentrations of lead (Pb), chromium (Cr), cadmium (Cd), and nickel (Ni) in sewage‐contaminated water were 18, 80, 88, and 210 times higher than in shallow handpump water, and 21, 133, 700, and 2200 times higher than in deep tube‐well water, respectively. The concentrations of Cd and Ni in shallow handpump underground water were significantly higher than in deep tube‐well underground water. The concentrations of Pb, Cr, Cd, and Ni in deep tube‐well water were 0.017, 0.003, 0.0002, and 0.0002 mg L^?1, respectively. Soils irrigated with sewage‐contaminated water had higher electrical conductivity, cation exchange capacity, organic carbon (C), and clay content but had lower pH and calcium carbonate content compared to soils irrigated with deep underground water. The concentrations of diethylenetriamine pentaacetic acid (DTPA)–extractable Pb, Cr, Cd, and Ni in soils irrigated with sewage‐contaminated water were 1.8, 35.5, 3.6, and 14.3 times higher, and total concentrations of these heavy metals were 1.5, 3.0, 3.7, and 2.2 times higher than that in soils irrigated with deep underground water. The mean concentrations of Pb, Cr, Cd, and Ni in crop plants growing on soils irrigated with sewage‐contaminated water were 4.88, 4.20, 0.29, and 3.99 mg kg^?1, which were 1.2, 2.1, 8.7, and 1.9 times higher than in plants irrigated with deep tube‐well water, respectively. The amounts of potentially toxic metals were significantly and positively correlated with cation exchange capacity and organic C content and negatively correlated with soil pH. In conclusion, long‐term accumulation of toxic metals in soils and their uptake by crop plants has a high potential for phytotoxicity as well as for entering into the food chain. The findings also suggest contamination of underground shallow drinking water through leaching of some highly mobile metals.     

Bioavailability of Inorganic Phosphorus Fractions in Calcareous Soils Estimated by Neubauer Technique,Iron‐Impregnated Filter Paper,and Chemical Tests

Abstract

Plants commonly suffer from phosphorus (P) deficiency in calcareous soils. Plant responses to P application on such soils mostly show poor correlation with their soil test P values. Experiments were conducted on 24 different soil samples under laboratory and greenhouse conditions to illustrate the relationship of various inorganic P fractions in different calcareous soils with P uptake by plants, P extraction by iron‐impregnated filter paper, and P soil test values estimated by 0.5M NaHCO₃ and ammonium bicarbonate diethylene triamine penta‐acetic acid. Total P in the 24 soils ranged from 652 to 1245 mgkg^?1 with a mean of 922 mgkg^?1. A major proportion (98%) of inorganic P was in HCl‐P (Ca‐bound) form. The HCl‐P (Ca‐bound) ranged from 296 to 729 with a mean of 480 mgkg^?1. The iron (Fe) and aluminum (Al)‐P (NaOH‐P) ranged from 0.92 to 12 mgkg^?1 with a mean of 1.57 mgkg^?1. The Fe‐P (citrate‐dithionite bicarbonate) ranged from 0.22 to 4.40 mgkg^?1 with a mean of 5.99 mgkg^?1. Data regarding P release from the soil matrix obtained by desorption with iron‐impregnated filter paper was best described by the Elovich equation. Range of slope and intercept values were found to be 5.48 to 17.3 and 17.23 to 56.27 mgkg^?1, respectively. Intercept values calculated for the Elovich equation may be related to labile P initially available for plant uptake in soils. Intercept values calculated for the Elovich equation correlated (r=0.77) significantly (p<0.01) with NaHCO₃ extractable (Olsen‐P)P. Significant correlation (p<0.05) of intercept with CDB‐P (r=0.44) and of slope with HCl‐P (0.43) suggested that the initially available P, regulated through CDB‐P, is replenished by HCl‐P [calcium (Ca) bound].     

Chemical Characterization of Inorganic Phosphorus Desorbed by Ion Exchange Membranes in Short‐ and Long‐Term Extraction Periods

Abstract

The chemical characterization of soil phosphorus (P) desorbed by anion and cation exchange membranes is of major importance to better understand which P forms are available to plants in short‐ and long‐term time periods. Two distinct soils, one acidic and one calcareous, were analyzed for P using two extraction procedures with mixed anion and cation exchange membranes. The short‐term (ST) experiment evaluated the effect of increasing the extraction periods up to 24 h, whereas the long‐term (LT) experiment consisted of a sequential extraction procedure using up to seven successive 24‐h extractions. In both experiments, the Chang and Jackson inorganic P fractionation methodology was carried out after each extraction treatment, and each treatment consisted of three replicates. Data were statistically analyzed by ANOVA and nonlinear regressions. In the ST experiment, increasing the extraction time increased the extracted P according to an asymptotic relationship (y=c?ab ^x ). Extracted P proceeded from the most labile fractions in the acidic soil. In calcareous soils, calcium phosphates may also contribute for extractable P. The LT experiment revealed that a single extraction, regardless of that extraction method, cannot predict the long‐term capacity of soils to supply P to the plants. An exponential relationship (P=a×n ^b ) was found between extracted P and the extraction number. Desorbed P proceeded from the most labile fractions in the acidic soil. However, in calcareous soils, some precaution is needed when considering the biological meaning of the results, because the occluded Fe phosphates also revealed significant decreases, probably due to the redox conditions in which these long extractions are performed.