The critical level of copper in sierozem soils of haryana as evaluated with different extractants

Summary The relative efficiency of seven extractants for estimating available Cu in sierozem soils of Haryana was studied. Bulk samples of 15 soils ranging in neutral normal amm. acetate extractable Cu from 0.12 to 0.20 ppm were subjected to screen-house study. The quantities of Cu extracted with neutral normal amm. acetate, Morgan’s reagent (pH 4.8)N ammonium acetate (pH 4.8), 0.1N HCl, 0.02M EDTA, critrate-EDTA and DTPA from soils were examined for their correlation with responses of maize in terms of Bray’s percentage yield and percentage Cu uptake. The highest coefficient of correlation was obtained between Cu extractable with neutral 1N NH₄OAc and Bray’s per cent yield and per cent Cu uptake. All other methods showed lower values of correlation. The critical level of available Cu estimated with use of neutral normal NH₄OAc was 0.16 ppm. Below this value, responses to applied Cu can be expected.     

Dilute hydrochloric acid as an extractant for available zinc,copper and boron in rice soils

Summary Because zinc deficiency is a widespread disorder of wetland rice and copper deficiency may occur with it, 0.05M HCl was compared with 0.1M HCl, EDTA and DTPA as an extractant for available zinc and copper. It was also compared with the reflux method for boron assay.Thirty-three wetland rice soils were analyzed for zinc and copper by the four methods. Rice was grown on the flooded soils, scored visually for zinc deficiency, and the plants analyzed for zinc and copper content. In the boron study, 53 soils were extracted by the reflux method and the 0.05M HCl procedure. Rice was grown on the flooded soils, scored visually for boron toxicity, and the plants analyzed for boron content.Fourteen of the 16 soils on which rice showed zinc deficiency gave <1.0 mg/kg Zn by the 0.05M HCl method but values far in excess of the critical limits by the other methods. The r values for available and plant zinc were: 0.05M HCl (0.88^**); 0.1M HCl (0.55^**); EDTA (0.43^**); and DTPA (0.31^ns).Twelve of the zinc-deficient soils gave<0.1 mg/kg Cu by the 0.05M HCl method but values exceeding the critical limits by the EDTA and DTPA methods. The r values for available and plant copper were: 0.05M HCl (0.74^**), 0.1M HCl (0.64^**), EDTA (0.28^ns), and DTPA (0.20^ns).The critical limit of 1.0 mg/kg by the 0.05M HCl extraction was confirmed for zinc deficiency and a tentative value of 0.1 mg/kg for copper deficiency proposed.The 0.05M HCl method separated boron-toxic soils from non-toxic soils and gave a better correlation (r=0.91^**) between available and plant boron than the reflux extraction (r=0.84^**). The toxic limit by the 0.05M HCl method was provisionally set at 4 mg/kg.     

Evaluation of suitable extractant for available lead in soils

Summary Four extractants were used to extract Soil-Pb from alluvial soils and the amounts of Pb extracted was correlated with Pb concentration in wheat crop. Of all the reagents, the Grigg's reagent was found to extract maximum amount of Pb from soils and the N NH₄OAc the least. A highly significant correlation (r=0.295) was observed between Grigg's reagent extractable Pb and Pb concentration in wheat plants followed by ammonium acetate (r=0.238). While 0.02M EDTA did not show any significant correlation, a negative significant correlation was observed with 0.1N HCl. re]19750512     

Studies on sulphur in vertisols

Summary Some soil and plant test methods were evaluated for predicting response of soybean crop (Glycine max (L.) Merr.) to S application in vertisols. Morgan's reagent, 500 ppm P containing Ca(H₂PO₄)₂.H₂O and KH₂PO₄ solutions, 0.5N NH₄OAc+0.25N HOAc and 0.15% CaCl₂ were found to be suitable extractants for measuring available soil S. The critical limits of extractable S were 9.0 ppm by Morgan's reagent, 10.0 ppm by phosphate solutions, 8.0 ppm by 0.5N NH₄OAc +0.25N HOAc and 14.0 ppm by 0.15% CaCl₂. Morgan's reagent was regarded as superior to other soil test methods in view of its high relationship with S uptake by plants, A values and relative yield. Critical S concentration in soybean plants varied with age. It was 0.15% and 0.185% for 36 and 60 days old plants, respectively. The critical N/S ratio on the other hand appeared to be constant at about 16.5 during vegetative growth period. Constancy of critical N/S ratio in plants was attributed to the near constancy of N/S ratio in plant proteins. There was highly significant relationship between response of soybean to S and to N, supporting the conclusion of some earlier workers that any soil showing large responses to N may not be supplying adequate S from the mineralization of soil organic matter.     

Effects of soil acidification on the chemical extractability of Fe,Mn, Zn and Cu and the growth and micronutrient uptake of highbush blueberry plants

Summary The effects of soil acidification and micronutrient addition on levels of extractable Fe, Mn, Zn and Cu in a soil, and on the growth and micronutrient uptake of young highbush blueberry plants (Vaccinium corymbosum L. cv. Blueray) was investigated in a greenhouse study.Levels of 0.05M CaCl₂-extractable Fe, Mn, Zn and Cu increased as the pH was lowered from 7.0 to 3.8. However, the solubility (CaCl₂-extractability) of Fe and Cu was considerably less pH-dependent than that of Mn and Zn. With the exception of HCl-and DTPA-extractable Mn, micronutrients extractable with 0.1M HCl, 0.005M DTPA and 0.04M EDTA were unaffected or raised only slightly as the pH was lowered from 6.0 to 3.8. Quantities of Mn and Zn extractable with CaCl₂ were similar in magnitude to those extractable with HCl, DTPA and EDTA whilst, in contrast, the latter reagents extracted considerably more Cu and Fe than did CaCl₂. A fractionation of soil Zn and Cu revealed that soil acidification resulted in an increase in the CaCl₂- and pyrophosphate-extractable fractions and a smaller decrease in the oxalate-extractable fraction.Plant dry matter production increased consistently when the soil pH was lowered from 7.0 to 4.6 but there was a slight decline in dry matter as the pH was lowered to 3.8. Micronutrient additions had no influence on plant biomass although plant uptake was increased. As the pH was lowered, concentrations of plant Fe first decreased and then increased whilst those of Mn, and to a lesser extent Zn and Cu, increased markedly.     

Effects of liming on the extractability of Fe,Mn, Zn and Cu from a peat medium and the growth and micronutrient uptake of highbush blueberry plants

Summary Levels of extractable micronutrients in a peat and the growth and nutrient uptake of young highbush blueberry plants (Vaccinium corymbosum L cv. Blueray) were studied in a greenhouse experiment in response to liming and two rates of addition of Fe, Mn, Zn and Cu.Levels of extractable micronutrients showed different trends with liming depending upon the extractant used and the element being considered. Levels of 0.05M CaCl₂-extractable Fe, Mn and Zn decreased as the pH was raised whilst those of Cu first decreased and then increased again. There was a general decline in 0.1M HCl-extractable Fe, Mn and Cu with increasing pH but levels of Zn were not greatly affected. Levels of 0.005M DTPA extractable Fe, Mn Zn and Cu generally declined but those extractable with 0.04M EDTA were either unaffected or increased as the pH was raised. Levels of CaCl₂-extractable Mn and Zn were the same order of magnitude as those extractable with HCl, DTPA and EDTA. In contrast, the latter reagents extracted considerably more Fe and Cu than did CaCl₂.Dry matter yields of plants were increased as the pH was raised from 3.9 to 4.3 but then decreased markedly as the pH was raised further to 6.7. With increasing pH, concentrations of plant Fe generally increased those of Mn were decreased and those of Zn and Cu were not greatly affected except for a marked decline in plant Cu at pH 6.7.     

Evaluation of phosphorus in forest soils: Comparison of phosphorus uptake,extraction method and soil properties

Summary Phosphorus in soils from plantation of red pine (Pinus resinosa Ait.) was determined using six extractants: 0.002N H₂SO₄ (pH 3.0); 0.025N HCl+ +0.03N NH₄F; 0.5N NaHCO₃ (pH 8.5);N NH₄OAc (pH 4.8); anion exchange resin (Dower –2, Cl-form); H₂O. Correlations of extractable P with Al- and Al-+Fe-P indicated that these fractions are the dominant forms of inorganic P in most of the soils.Uptake of P by corn and Monterey pine seedlings grown in greenhouse culture was correlated with soil P extracted by the different methods. The most successful of the extractants for predicting P uptake was resin extractable P; the simple correlation coefficients were 0.811 and 0.609 for pine and corn respectively. P uptake by pine correlated significantly with 0.002N H₂SO₄ P (r=0.679),N NH₄OAc P (r=0.443), H₂O P (r=0.549) and Al-+Fe-P (r=0.532) while P uptake by corn correlated with 0.002N H₂SO₄ P (r=0.579), H₂O P (r=0.477) and organic P (r=0.460). Per cent P in pine seedling tops correlated significantly with 0.002N H₂SO₄, resin andN NH₄ OAc extractable P. Multiple regressions which included silt+clay and organic P improved correlations of some soil tests with P uptake in corn and pine seedlings respectively.Research supported by the School of Natural Resources, College of Agricultural and Life Sciences, Univ. of Wisconsin, Madison, the Wisconsin Department of Natural Resources and FAO Fellowship to the senior author.     

Phosphate supplying power of rock phosphates in an oxisol

Summary The P-supplying power of triple superphosphate, three apatitic rock phospates and a calcined aluminum rock phosphate were tested by measuring the quantities of fertilizer P recovered in soybean and in four chemical extractants, after 3-day and 75-day periods of contact between soil and fertilizer.The triple superphosphate supplied the highest amounts of P, but it lost efficiency during the longer incubation period. The rock phosphates maintained their original efficiencies, probably as a result of a balance between P released from the fertilizer and P converted into non-labile forms.The following coefficients of correlation between P uptake by soybean from an acid oxisol and P extracted by chemical extractants, after the two incubation periods, were found: 0.902^** for 0.01M CaCl₂; 0.823^** for anion-exchange resin; 0.720^** for 0.03N NH₄F+0.025N HCl; –0.037 (n.s.) for 0.025N H₂SO₄+0.050N HCl.The acid NH₄F solubilized residual calcined aluminum phosphate particles, and double acid extracted P from residual apatite particles, thus accounting for their poorer performances in predicting availability of fertilizer P.The relative efficiencies of the rock phosphates could largely be predicted after an incubation period of only three days. This finding attests to the presence in these rock phosphates of an easily soluble fraction of P which is not indicative of the degree of reactiveness of the phosphate as a whole.on leave at the Agricultural University during 1977.     

Phytoalexin production in lucerne roots inoculated withVerticillium albo-atrum

Summary Out of various soil and plant test methods tested for predicting response of rice to K application in soils of a rice growing valley region the Hanway and Heidal extractant neutralN NH₄ OAc turned out to be the best. The critical limit of extractable K was 160 ppm by the Hanway and Heidal extractant, and by the Bray's reagent 175 ppm. Critical K level in the rice plant is 0.4%. Correlations between the extractable K and K uptake were highly positive for various extractants: Hanway and Heidal, Morgan, Hunter and Pratt No. 2, Blanchet and Perigand and MacLean. Although majority of the soils of the region was Inceptisols followed by Alfisols and Vertisols, all soil types had a similar available nutrient status and a similar pattern in relative grain yields. K response was noticeable in Alfisols with respect to grain and straw yields. The grain P concentration in Vertisols, and straw K in Alfisols indicated the contribution of K towards the productivity of two soil groups.     

Soil isotopically exchangeable zinc: A comparison between E and L values

The objectives of the present paper were: (i) to determine isotopically exchangeable zinc using two isotopic exchange methods (E and L values) in a series of polluted and non-polluted Swiss agricultural soils, and (ii) to evaluate the ability of chemical extraction methods to estimate plant-available soil Zn using isotopic techniques. The surface horizon (0–20 cm) of seven polluted and non-polluted soils representing a wide range in physico-chemical properties and Zn contents were sampled. An isotopic exchange kinetics (IEK) approach was used to assess, in a batch experiment, the isotopically exchangeable Zn content (E value). In order to determine the L values, a pot experiment was carried out with Lolium multiflorum (cv. Axis) in a growth chamber using a ⁶⁵Zn-isotope dilution technique. Total Zn uptake and the isotopic composition (⁶⁵Zn/^stableZn) were determined in Lolium multiflorum for five successive cuts. The amounts of zinc extracted by different chemicals were compared with L values and regression parameters were estimated. The isotopic composition in soil extracted by DTPA and EDTAAc at the end of the pot experiment was also determined. Results showed that the equation describing the increase of isotopically exchangeable Zn with time could be extrapolated to three months for polluted and non-polluted neutral and acidic soils, and that the results were not different from the amount of isotopically exchangeable Zn experimentally determined with Lolium multiflorum (L value). In alkaline soils however, results suggest that either ⁶⁵Zn sorption occurred in the batch experiment or that the concentration of Zn in the soil solution had been overestimated, leading to an overestimation of the E value compared to the L values. Furthermore, the specific activities measured in DTPA and EDTA extractions at the end of the pot experiment were significantly different compared to the specific activity of the plant, showing that both these chelating agents extract neither all the available soil Zn nor only the available soil Zn for plants. Abbreviations: C _Zn– concentration of Zn in a soil water extract (mg Zn L^?1); C _Zn?Plant– concentration of Zn in plant shoots (mg Zn kg^?1 DM); DTPA – diethylene triamine pentaacetic acid; E _1\min– amount of Zn isotopically exchangeable within one min (mg Zn kg^?1 soil); E _(t)\exp– amount of Zn isotopically exchangeable after t min derived from experimental results (mg Zn kg^?1 soil); E _(t)pred– amount of Zn isotopically exchangeable after t min predicted using kinetic parameters derived from a 100 min long isotope exchange kinetic experiment together with C _Zn, and Zn_HNO3 (mg Zn kg^?1 soil); EDTA – ethylene diamine tetraacetic acid; IC_P– isotopic composition of Zn in plant shoots; IC_DTPA– isotopic composition of Zn in the soil DTPA extract; IC_EDTA– isotopic composition of Zn in the soil EDTA extract; IC_SE– isotopic composition of Zn in the soil extracts; IEK – isotope exchange kinetics; L value – amount of plant available Zn (mg Zn kg^?1 soil); Lolium multiflorum; TEA – Triethanolamine; Zn_DTPA– Zn extractable by 0.005 M DTPA + 0.01 M CaCl2 + 0.1 M TEA; Zn_EDTA?NH4Ac– Zn extractable by 0.5 M NH₄Ac, 0.02 M EDTA; Zn_{EDTA?Ca(NO3)2}– Zn extractable by 0.005 M EDTA, 0.01 M Ca(NO₃)₂; Zn_KCl– Zn extractable by 1 M KCl; Zn_CaCl2– Zn extractable by 0.01 M CaCl₂; Zn_NaNO3– Zn extractable by 0.1 M NaNO₃; Zn_HNO3– Zn extractable by 2 M HNO₃.     

Soil-sodicity-induced zinc deficiency in maize

Summary Maize (Zea mays L. cv. Ganga-2) plants were grown in pot culture on a loamy alluvial soil of Lucknow district (India) alkalinized to graded levels of ESP (Exchangeable Sodium Percentage) ranging from 15.5 to 55.3. Before sowing maize seeds the soil was fertilised with NPK, Fe, Mn and Cu. At and above ESP 34 Zn-deficiency symptoms first appeared at 30 days. The symptoms gradually became pronounced with increase in age and at 60 days they were found even at ESP 15.5. The severity of symptoms was related to increase in sodicity. Alkalinization of soils depressed available soil Zn and tissue Zn and increased tissue ratios of Na/Zn and P/Zn. It also decreased the total plant content of Zn, Fe, Mn, Cu and even Na. Increase in soil sodicity increased both tissue concentration and total content of P in plants upto ESP 34 beyond which it decreased it. Among different extractants, 0.1N HCl, DTPA pH 7.3 and EDTA-(NH₄)₂ CO₃ pH 8.6, for measuring available soil Zn the latter showed best correlations with soil ESP (−), tissue P (−), P/Zn ratio (−), dry matter yield (+) and tissue Zn (+). Tissue Zn was related to yield (+), tissue Na (−) and soil ESP (−). Mild, moderate, severe and very severe Zn deficiency in maize was induced by soil ESP levels, 18, 25, 33 and 45, respectively.     

Contribution of zinc fraction to available zinc extracted,by some chemical methods,from rice growing soils of North-Western Himalayas

A laboratory and greenhouse investigation was undertaken to study the distribution and contribution of zinc fractions to available zinc in submerged rice. Most of the total zinc was present as Al- and Fe-oxide bound (52.8%) and residual zinc (27.8%). The exchangeable (non-specifically and specifically absorbed), organically bound and Mn-oxide bound zinc fractions averaged 0.7, 1.1, 6.3 and 4.9 per cent of the total zinc, respectively. 0.1 M HCl, EDTA-(NH₄)₂CO₃ and dithizone extractants showed significant correlation with per cent yield, Zn concentration and zinc uptake by grain and the critical limits were 3.0, 1.9 and 1.0 µg^–1, respectively. Organically bound zinc exhibited significant correlation with per cent yield and zinc uptake by grain whereas specifically absorbed zinc correlated with Zn concentration in grain. Mn-oxide boudn zinc and Al- and Fe-oxide bound zinc fractions were also correlated with zinc concentration and zinc uptake by grain.     

Efficiency of zinc fertilization for flooded rice

Summary Several Zn-deficient soils from the major rice growing areas in the USA were characterized with respect to extractable and labile Zn and other parameters including available P, pH, organic matter, and cation exchange capacity. A greenhouse experiment was conducted to determine whether the above factors influence the response of several rice cultivars to ZnSO₄ or ZnEDTA applied as a mixed preplant treatment or to the floodwater at panicle initiation.Response of the rice to Zn varied widely among soils with labile Zn (L value) being a poor indicator of Zn availability and soil pH, and DTPA or 2 N MgCl₂ extraction of Zn being the most reliable indices. Soil incorporation prior to flooding was more effective than floodwater application for the initial crop, but both methods of placement were comparable for a subsequent ratoon crop. In either situation, ZnSO₄ was superior to ZnEDTA. Recovery of Zn from ZnSO₄ was generally less than 5 percent where Zn response was obtained and up to 14 percent from nonresponsive soils.     

Influence of FeEDDHA and soil temperature on the growth of two soybean varieties

Bulk samples of 30 surface soils characterized in the National Cooperative Soil Survey of Louisiana were collected at the original sites and planted with sorghum-sudangrass in the greenhouse. The native K was exhausted by a total of four croppings. The available soil K was extracted with 1N NH₄OAc 7.0 and 0.1N HCl while the difficultly available-K was extracted by 0.3N NaTPB (sodium tetraphenylboron). In addition, the mica content was estimated by differential dissolution. All soils except Dundee produced the greatest dry matter yield in the first crop with steadily decreasing production in the succeeding crops. The same pattern was shown in the K uptake. It appears that the first crop removed a large portion of the exchangeable K. There was a high degree of relationship between plant uptake of K and exchangeable K in the soils (r²=0.89^**). Uptake by the subsequent crops was generally controlled by the K in the micaceous minerals (r²=0.89^**). Since there was a high coefficient of determination between mica-K and difficulty available-K (r²=0.91^**) one also finds that uptake of K by crops 2, 3 and 4 was also well correlated to difficultly available K (R²=0.94^**). The uptake of K that was not originally in the exchangeable form was also highly related to difficultly available-K (R²=0.51^**). Contribution from the Department of Agronomy, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge. Part of the M.S. theses of the senior authors. Former Graduate Students and Prof. of Agronomy, respectively.     

The effects of cropping corn on the extractability of zinc added to a calcareous soil

The effects of cropping corn on the decrease in the extractability of Zn added to a calcareous soil were studied by a pot experiment and chemical extractions. The results show that the concentrations of Zn exchangeable with MgCl₂ (EXC-Zn) and extractable with DTPA (DTPA-Zn) in the soils with added Zn decreased with time. The processes associated with the decrease in extractability in DTPA of Zn added to soil can be described aptly by a diffusion equation which gives the proportion of added Zn in the non-DTPA fraction as a function of the square root of incubation time. This result suggests that the diffusion of Zn cations into microporous solids is a rate-limiting reaction. The relative diffusion rate coefficients (D/r²) were found to be 1.95×10^-10 and 3.34×10^-10 sec^-1 in the soils with added Zn of 20 and 60 mg kg^-1, respectively. Compared with uncropped soil, the concentrations of DTPA-Zn in the soils with added Zn were decreased by cropping. The decrease of DTPA-Zn in the soils in the presence of corn can be attributed to both its acquisition by corn and other processes associated with the growing of corn. The activity of plant roots would appear to enhance the process of decrease in the extractability in DTPA of Zn added to the soil. The source of Zn uptake by corn was affected by the loading or activity of Zn in soil. In the soil with low available Zn, the DTPA non-extractable Zn (non-DTPA-Zn) was mobilized and taken up by corn. In the soils with high available Zn, e.g. the recently added Zn, only EXC-Zn and a part of the DTPA-Zn were taken up by corn.     

Sulfur in Ghanain soils

Sulfur availability in twenty selected surface soils (0–22 cm), which varied in both physical and chemical properties and sampled under cultivated and uncultivated management in the various ecological zones of Ghana, was studied. Texture varied from coarse sand to clay, with 16–85% sand and 10–51% clay. Organic C varied from 0.45 to 2.24% and total N from 0.034 to 0.215%; soil pH (0.01M CaCl₂) from 3.69 to 7.43 and total S from 44 to 273 ppm. Inorganic sulfate formed 2.3 to 14.8% of the total S, HI-reducible S 4.4 to 28.2, C-bonded S 4.4 to 28.2 and unidentified organic S 12.7 to 63.2%. Sulfur availability was assessed by chemical extraction methods and electroultrafiltration technique as follows: (i) extraction with Ca(H₂PO₄)₂·H₂O solution containing 500 ppm P, (ii) extraction with 0.1M LiCl and (iii) electroultrafiltration (EUF) at 80°C, 400 V for 10 min and also on seven of the soils the standard EUF fractionation procedure of Neméth. Ca(H₂PO₄)₂-extractable S was not significantly correlated with LiCl-extractable S nor with any of the EUF values. LiCl-extractable S was not significantly correlated with sulfate extractable by and EUF?1+2+3 fractions (r=0.911^**). Dry matter yield of oat seedlings and EUF?1+2+3 fractions (r=0.911^**). Dry matter yield of oat seedlings was not correlated with any of the availability indexes. Total S uptake was significantly correlated with LiCl-extractable S (r=0.629^** without S and 0.729^** with S applied) and with EUF-80°C, 400 V/10 min (r=0.561^**), EUF-1 (r=0.953^***) and EUF-2 (r=0.912^**). On all the soils, more S was taken up by oat plants than could be accounted for by the inorganic S and S mineralized from organic S during an incubation period of 4 weeks.     

Analysis of field-moist Cd contaminated paddy soils during rice grain fill allows reliable prediction of grain Cd levels

Research undertaken over the last 40 years has confirmed that the long-term consumption of cadmium (Cd) contaminated rice contributes to human Cd disease. Rice is the staple of millions throughout South and Southeast Asia. Therefore, the ability to accurately assess the risk of rice grain Cd uptake in areas of elevated soil Cd would be a pre-requisite to protecting public health and regional export security. During 2001–2002, 308 concomitant soil and rice grain samples were collected from a Cd/Zn co-contaminated site in Western Thailand and determined for aqua regia digested soil Cd and rice grain Cd. No significant relationship was observed between total soil Cd and rice grain Cd (r ² = 0.117). This intuitively is to be expected since total soil Cd bears no relationship to phyto-available Cd. Similarly no relationship was observed between 0.005 M DTPA extractable soil (air-dry) Cd and rice grain Cd (r ² = 0.165). Again this result could have been predicted as the phyto-availability of Cd in paddy soils is a function of the complex interaction between soil pH, redox conditions and the presence of competing ions. Consequently, in 2003 a further study was undertaken to assess the effectiveness of commonly utilized soil extractants namely, 0.1, 0.05 and 0.01 M CaCl₂ solutions at a soil extractant ratio of 1:5 and 1 M NH₄NO₃ for 2 h or 4 h extractions times at a soil/extractant ratio of 1:2.5. Soil samples were collected at the critical rice grain fill stage and sub-divided into Portion A which was subjected to conventional air-drying and sample preparation procedures and Portion B which was maintained at Field Condition (FC) and stored at <4°C until extractions were undertaken. Concomitant rice grain samples were collected at maturity. The results indicate that air-dried soil samples subjected to conventional soil preparation procedures were totally ineffective at predicting the uptake of Cd by rice stem, leaf or grain, regardless of extractant. Further, the results indicate that the Stepwise Regression model incorporating 0.1 M CaCl₂ extractable Cd and soil pH_w determined on field moist samples accounts for 63.8% of the variability in rice grain Cd.     

Chemical speciation of Zn in acidic soils: suitable soil extractant for assessing Zn availability to maize (Zea mays L.)

Abstract

Chemical fractions of soil Zn namely: water soluble (WS), exchangeable (EX), Pb displaceable (Pb-disp.), acid soluble (AS), Mn oxide occluded (MnOX), organically bound (OB), amorphous Fe oxide occluded (AFeOX), crystalline Fe oxide occluded (CFeOX), residual (RES) were determined in 20 surface (0–15 cm) samples of acidic soils from the provinces of Uttarakhand and Uttar Pradesh, India. The chemical fractions of soil Zn in acidic soils were found to be in the following descending order of Zn concentration: RES > CFeOX > Pb-Disp. > AFeOX > MnOX > AS > OB > EX > WS. These soil samples were also extracted by: DTPA (pH 7.3), DTPA (pH 5.3), AB-DTPA (pH 7.6), Mehlich 3 (pH 2.0), Modified Olsen, 0.01 N CaCl₂, 1 M MgCl ₂ and ion exchange resins. Chemical fractions and the soil extractable content of Zn estimated by different soil extractants were significantly correlated with some general soil properties. Maize (cv. Pragati) plants were grown in these soils for 35 days after emergence and Zn uptake by plants was compared with the amount of Zn extracted by different soil extractants and chemical fractions of Zn. Among chemical fractions of soil Zn, Pb-displaceable and acid soluble chemical fractions of soil Zn showed a significant and positive correlation with Zn uptake by maize. Path coefficient analysis also revealed that the acid soluble Zn fraction showed the highest positive and direct effect on Zn uptake (P=0.960). Among different multinutrient soil extractants evaluated for their suitability to assess Zn availability in acidic soils, DTPA (pH=5.3) was most suitable soil extractant, as the quantity of soil Zn extracted by this extractant showed a significant and positive correlation with the dry matter yield, Zn concentration and uptake by maize plants.     

Soil flushing of a sandy loam contaminated with Pb(II), PbS4 (s), PbCO3 (3), or Pb‐Naphthalene: Column results

Column‐scale oil flushing of a sandy loam contaminated with either Pb(II) (500 mg/kg Pb), PbSO₄ (10,000 mg/kg Pb), PbCO₃ (10,000 mg/kg Pb), or Pb‐naphthalene (400 mg/kg Pb, 333 mg/kg naphthalene) was investigated. HCl (0.1 N), EDTA (0.01 M), and CaCl₂ (1.0 M) were selected as the soil‐flushing solutions based on soil‐washing experiments. For the Pb‐only tests, Pb removal efficiencies were 85, 100, and 78% for HCl, EDTA, and CaCl₂, respectively. For PbSO₄ (s), Pb removal efficiencies were 32, 100, and 96% for HCl, EDTA, and CaCl₂, respectively, and for PbCO₃ were 97, 100, and 14% for HCl, EDTA, and CaCl₂, respectively. Larger amounts of flushing solutions were required for the remediation of PbSO₄‐and PbCO₃‐contaminated soils compared with the Pb‐only tests, most likely because of slower dissolution kinetics and the neutralization of HCl by CO₃ ^‐2 For Pb‐naphthalene, Pb removal efficiencies were 78 and 72% for HCl and EDTA, respectively, which compared well with soil‐washing results but were less than those observed in Pb‐only column studies.     

The profile distribution of total and extractable boron in cacao-growing soils in southwestern Nigeria

The profile distribution of total and extractable B was determined in 16 Nigerian cacao-growing soil profiles formed from different parent materials. Total B for all soils ranged from 8 to 54μgg⁻¹ with a mean of 24μgg⁻¹. The soils formed from sandstones in the rainforest zone contained higher amounts of total B than soils derived from basement complex. Boron extractable in hot water, in 0.1% CaCl₂, and in 1N NH₄OAc varied from 0.13 to 1.38, 0.44 to 1.20 0.03 to 0.56μgg⁻¹ respectively. The corresponding means were 0.66, 0.75 and 0.27μgg⁻¹ B. Soils on metamorphic rocks gave the highest values. All extractable B values were related to organic matter while only CaCl₂-extractable B correlated with total B. Generally total and extractable B values were higher in the top soils than in the subsoils.