DTPA Soil Research Articles

Biogeochemistry of Pb–Zn gossans, northwest Queensland, Australia: Implications for mineral exploration and mine site rehabilitation

Abstract The concentration and distribution of metals were studied in metallophytes, growing on and in the vicinity of Pb–Zn gossans, NW Queensland. The study investigated the accumulation of metals in plant species and assessed their potential use as indicators in geobotanical and biogeochemical prospecting and as metal excluders in mine site rehabilitation. Plant species colonising the gossans tolerate high concentrations of metals. Total mean metal concentrations of soils ranged from minima of 14 ppm Cu, 28 ppm Pb and 34 ppm Zn in background areas to maxima of 660 ppm Cu, 12000 ppm Pb and 2100 ppm Zn over mineralised soils. Over the gossans, the grass species Eriachne mucronata forma, Enneapogon lindleyanus and Paraneurachne muelleri replace the characteristic grass Triodia molesta where the soils have high Pb and Zn concentrations. Of the 16 plant species identified, 3 of them, Hybanthus aurantiacus, Clerodendrum tomentosum and Bulbostylis barbata, were confined to the gossan sites. B. barbata appears to be of particular use in geobotanical prospecting as it indicates base metal mineralisation in the region. The biogeochemical analyses indicate significant enrichment of Cd, Pb and Zn in the tissue of all plant species, with the abundance of Cd, Pb and Zn in dried vegetation from the gossans being up to one order of magnitude above background. In particular, the uptake of Cd, Pb and Zn by Sida sp., T. molesta, Cleome viscosa and Eriachne mucronata forma increases linearly with DTPA-extractable soil metal concentrations. The biogeochemistry of these plants provides the best anomaly definition of the exposed gossans. Furthermore, the analysis of roots demonstrate that the plant species T. molesta, Eriachne mucronata forma and P. muelleri allow the transport of Cd, Pb and Zn from the roots to the above-ground biomass. Hence, the species best suited for biogeochemical prospecting for base metals in the region and semi-arid inland northern Australia are Eriachne mucronata and the genus Triodia. The analyses also reveal differences in the ability of each species to accumulate metals. Among all gossan plants, Eremophila latrobei displays distinctly low Pb concentrations and low correlations with soil DTPA extractable Pb. This plant is the most efficient in excluding Pb from its biomass, making it most suitable for the revegetation of Pb contaminated soils. This study demonstrates that biogeochemical examinations of gossans can reveal indicator and excluder plants, which are of potential use in mineral exploration as well as mined land reclamation.

Estimating the long-term residual value of zinc oxide for growing wheat in a sandy duplex soil

A long-term (17-year duration) field experiment was started on newly cleared zinc (Zn)-deficient sandy duplex soil (sand with lateritic ironstone gravel over clay) in south-western Australia that had never been fertilised to measure the residual value of Zn oxide for growing spring wheat (Triticum aestivum L.). When wheat was grown in the field experiment different amounts of Zn were applied once only to plots in 1983, 1984, 1986, 1990, 1992, 1996, 1997, and 2000. When the field experiment was terminated, we collected soil samples from the top 0.10 m of the field plots to do a glasshouse experiment reported here. In the pot experiment 5 amounts of Zn were applied to subsamples of soil collected from each plot of the field experiment. When a yield increase (response) to the freshly applied Zn was obtained in the pot study the maximum yield plateau for the relationship between yield of 54-day-old dried wheat shoots and the amount of Zn freshly applied was similar regardless of when and how much Zn was applied in the field. The amount of Zn freshly applied to soil in the pots required to produce 90% of the maximum yield of dried wheat shoots was determined for soil previously treated with no Zn or different amounts of Zn in different years in the field to provide DM90 values. The DM90 values were largest when no Zn was applied in the field, decreased as more Zn was applied in the field and, for each amount of Zn applied in the field, increased as the number of years from application of Zn increased. For soil treated with 0.5 and 1.0 kg Zn/ha in the field the relationship between DM90 values and the number of years since Zn was applied in the field was approximately linear. The projected number of years taken for soil previously treated with Zn in the field to require the same DM90 values as soil samples collected from the nil-Zn treatments in the field was 23 and 40 years for the 0.5 and 1.0 kg Zn/ha treatments, respectively. In the pot experiment the Zn concentration in plant parts that was related to 90% of the total yield of dried wheat shoots (critical Zn concentration) was ~12 mg/kg for youngest mature growth (YMG) and 22 mg/kg for rest of shoots (ROS). The relationship between yield of dried wheat shoots and DTPA soil test Zn before sowing was similar for all the Zn treatments applied in both the field and pot studies, and the critical value was ~0.17 mg Zn/kg soil.

Reduction of Cadmium Availability to Tobacco (Nicotiana tabacum) Plants using Soil Amendments in Low Cadmium-contaminated Agricultural Soils: A Pot Experiment

Cadmium (Cd) concentration in field-grown tobacco leaves usually ranges from < 0.5 to 5 mg Cd kg–1 dry matter (DM). Reducing bioavailability of soil Cd by adding amendments to the soil could be suitable to mitigate Cd uptake by tobacco plants. However, little is known on the effect of inorganic amendments on agricultural soils with low Cd concentrations. Therefore, we performed a pot experiment with tobacco plants that were grown during 56 days in two neutral to alkaline agricultural soils with low total Cd concentrations (soil 1 = 0.4, soil 2 = 0.7 mg kg–1). Both soils were amended or not with 1 or 5% of sepiolite, zeolite, hydroxyapatite and apatite II™. Major and trace elements were measured in mid-stalk position leaves. Soil metals were measured in a DTPA soil extraction to assess the effect of the amendments on metal bioavailability. Some amendments significantly reduced Cd concentration in tobacco leaves, but the effect differed between the two soils tested. In soil 1, the use of zeolite at the 1% dose was the most efficient, reducing the average Cd concentration from 0.6 to 0.4 mg kg–1. In soil 2, the 5% hydroxyapatite treatment led to the maximal reduction in Cd concentration (50%), with an average final Cd concentration in leaves of 0.7 mg kg–1 (control: 1.5 mg kg–1). There was a dose effect for some amendments in soil 2 (containing more Cd), suggesting a reduced efficiency of the amendment at the lowest addition rate. DTPA extractable Cd and Zn measured at the end of the pot experiment were correlated to the metal concentrations in tobacco leaves suggesting that (1) the reduction in leaf Cd concentration was due to a reduction in metal availability to tobacco and (2) DTPA may be a suitable extractant to estimate Cd availability to tobacco plants in these two soils. In addition, a batch experiment was performed with the same soils to test a larger number of amendments, including the four tested in the pot experiment. Results were compared to those of the pot experiment to assess whether a batch experiment may predict the efficiency of an amendment on a given soil. It gave results compatible with those from the pot experiment except for the sepiolite and highlighted the broad range of potential amendments available for heavy metal remediation in crop plants.

Increased risk of zinc deficiency in wheat on soils limed to correct soil acidity

Addition of lime to ameliorate soil acidity has been observed to induce zinc (Zn) deficiency for wheat in sandy soils of south-western Australia, reducing grain yields. The implications of widespread use of lime to treat acid soils for the residual value of Zn in these soils are not known. In a glasshouse experiment, using a Zn-deficient sand from south-western Australia, 3 levels of finely powdered calcium carbonate were added and incubated in moist soil for 6 weeks at 22°C to produce three different pH values (1 : 5 soil : 0.01 m CaCl2): 4.9 (original soil not treated with calcium carbonate), 5.8, and 7.4. Five amounts of Zn, as solutions of Zn sulfate, were then incubated in moist soil for 0, 30, 60, 120, and 180 days before sowing spring wheat (Triticum aestivum L.). The residual value of the applied Zn was determined using yield of dried shoots, Zn content in dried shoots, and soil test Zn (DTPA extraction). This was done by calculating the effectiveness of the incubated Zn for all 3 soils relative to the effectiveness of Zn applied just before sowing wheat (0 day incubation, freshly applied Zn) for the soil not treated with calcium carbonate. As measured using yield of dried shoots, Zn content of dried shoots, or soil test Zn, the residual value of the incubated Zn decreased with increasing soil pH and with increasing period of incubation of Zn with moist soil before sowing wheat. The critical Zn concentration, associated with 90% of the total yield of dried wheat shoots, was (mg Zn/kg) 13 in the youngest mature growth (apex and youngest emerged leaf), and 20 for rest of dried shoots. These values were similar to current critical values for unlimed soils. The relationship between yield of dried shoots and DTPA soil test Zn was similar for unlimed and limed soils, so similar critical soil test Zn was applicable on the sandy soil regardless of soil pH. Critical DTPA soil test Zn, the soil test Zn that was related to 90% of the maximum yield of dried shoots, was 0.14 mg Zn/mg soil. To combat the increased risk of Zn deficiency on soils limed to ameliorate soil acidity, fertiliser Zn needs to be re-applied to the soil when soil and plant tests indicate a high likelihood of deficiency.

Cadmium uptake by tobacco as affected by liming, N form, and year of cultivation

Tobacco is able to accumulate cadmium and reduction of cadmium content can reduce health hazards to smokers. Soil pH and form of N fertilizers are among the factors affecting Cd uptake by tobacco. This hypothesis was tested in an acid soil in northern Greece by a four year field experiment. The variability of Cd uptake by tobacco was attributed to the variation of soil Cd availability as affected by soil pH. Liming with 3000 kg Ca(OH) 2 ha −1 increased soil pH by 0.8 units and decreased extractable with DTPA soil and leaf Cd by 40% and 35%, respectively. The ammonium fertilizer caused the opposite, but weaker, effects. Liming reduced soil Cd more in the ammonium treatment than in nitrate or combined N treatments. The year of cultivation strongly affected soil and leaf Cd. Four years after tobacco cultivation, soil pH was reduced by 0.5 units, whereas soil and leaf Cd reduction was more than 60% in the limed treatments. Liming affected Cd uptake only in the first three years of cultivation.

LONG-TERM CHANGES IN THE EXTRACTABILITY AND AVAILABILITY OF LEAD, CADMIUM, AND NICKEL IN SOILS UNDER WASTEWATER IRRIGATION

The objective of this study was to assess the long-term changes in the behavior of extractable and bioavailable lead (Pb), cadmium (Cd) and nickel (Ni) of soils in the Mexican Valley of Mezquital under wastewater irrigation. Soil samples (0–10 cm depth) were collected from sites with different years of irrigation management for the analysis of heavy metals. Plant tissue was also collected to determine their Pb, Cd and Ni concentrations. Statistical analyses were carried out to compare HNO3, EDTA and DTPA soil tests and to relate amounts of heavy metals extracted from the soils to their levels in plant tissue. Results showed that metal concentrations, in general, tended to increase in soil with increasing number of years of irrigation. Correlation coefficients were poor between HNO3–Ni and EDTA–Ni or DTPA–Ni of the soils, while the correlation between HNO3–Cd and EDTA–Cd was only moderate and significant between HNO3–Cd and DTPA–Cd. Significant correlation was found between lead extracted from the soil by the chelates (EDTA/DTPA) and HNO3. Leaf Pb and Cd concentrations of wheat from the soils explained 66 and 78% of the variability of their respective levels in wheat seed. Although Ni concentrations in leaf and seed of wheat were poorly related, content of this metal and that of Cd were higher in the latter plant organ in most sites, suggesting the absence of a physiological barrier in the transfer of metal from plant vegetative tissue to storage organ and reflecting a matter of concern about the consumption of this grain by animal or human population.

Effect of phosphorus, potassium and zinc fertilizers on iron toxicity in wetland rice ( Oryza sativa L.)

During the period January–August 1996, an investigation was carried out in La Mata, Cotui, Dominican Republic with the objective to study the effect of P, K and Zn fertilizers on Fe toxicity in the rice varieties JUMA-57 (sensitive to Fe toxicity), ISA-40 and PSQ-4 (both tolerant to Fe toxicity). The rate of fertilizer application was 22 and 62 kg P ha−1; 58 and 116 kg K ha−1; 3 and 7 kg Zn ha−1 and a constant dose of 140 kg N ha−1 and 40 kg S ha−1 on all fertilized plots. The control received no fertilizer. JUMA-57 was the only variety that showed symptoms of Fe toxicity. The observed symptoms showed a yellow to orange colour. Symptoms of Fe toxicity appeared first one week after transplanting (WAT), decreased at the fourth WAT, but returned six WAT and continued until the end of the experiment. Fertilizer application reduced symptom intensity and increased grain yield in all varieties, but only JUMA-57 did not reach the maximum yield typical for that variety. Fertilizer application did not completely overcome the toxicity effect, i.e. in symptom intensity and grain yield. The positive effect of fertilizer application could not be attributed to a specific nutrient. Intensity of symptoms was not related to Fe concentration in the leaves. The average Fe concentration of 108 mg kg−1 was not high enough to be considered toxic. Symptoms could not be explained through Mn toxicity (average Mn concentration in the leaves was 733 mg kg−1) nor Zn deficiency (average Zn concentration in the leaves was 20 mg kg−1). There was a clear relationship, though, between soil DTPA extractable Fe and symptom intensity or grain yield. The toxic effect was observed when the DTPA extractable Fe in the flooded soil was above 200 mg kg−1. From these results, we concluded that the Fe toxicity resulted from high Fe in the root zone and not from high Fe concentrations in the leaves.

Reference concentrations for heavy metals in mineral soils, oat, and orchard grass (D�ctylis glomer�ta) from three agricultural regions in Norway

Background values for heavy metals are necessary for the assessment of metal pollution of soils and plants. Samples of cultivated and uncultivated soils, oat grain, and seed heads of orchard grass (Dactylis glomerata) were collected from central, southeastern, and southwestern Norway. Total and easily extractable concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were determined in soil samples and total concentrations in plant samples. Element distributions have been correlated with petrology of soil parent material, type of mineral deposit, soil depth, geographic area, and land use. Concentrations of heavy metals are generally within the lower part of the normal global range. The petrology of the soil parent material has the greatest influence on aqua regia extracted metal concentrations among the factors studied. DTPA extracted metals show less dependence on rock types. Presence of alum shale results in particularly high values for Cd in both soil extracts and in oat grain. Soil cultivation seems to influence the relative concentration of metals in the topsoil. The ratios of easily extractable to total concentrations of metals are primarily related to the organic matter content. Metal concentrations in oat grain can best be predicted by concentrations in DTPA extracts and soil pH among the factors studied. Seed heads of orchard grass are less affected by concentrations in the soil and appear therefore to be a poor indicator of heavy metals in soils.

Comparison of soil zinc extractants for detection of applied zinc and prediction of leaf zinc concentration

Abstract Many soil extractants have been developed for determination of zinc (Zn) availability to plants. The optimum soil Zn extractant should be useful not only for prediction of plant Zn concentration but also for detection of applied Zn levels. The objectives of this study were: i) to compare soil Zn extradants for detecting applied Zn and for predicting peanut leaf Zn over a range of soil pH levels, and ii) to correlate other soil‐extractable Zn levels with Mehlich‐1. Soil and peanut leaf samples were taken from a field study testing pH levels as the main plots and Zn application rates in the sub‐plots. Extractable Zn was determined on soil samples using Mehlich‐1, Mehlich‐3, DTPA, MgNO3, and many dilute salt extradants of varied strength and pH. Correlation of extractable soil Zn to cumulative applied Zn levels revealed Mehlich‐1, Mehlich‐3, DTPA, and AlCl3 extradants to be among the best indicators of applied Zn. Leaf Zn concentration was best correlated with soil Zn extracted by dilute salts, such as KCl, CaCl2, NH4Cl, CaSO4, and MgCl2. Including soil pH as an independent variable in the regression to predict leaf Zn considerably improved R‐square values. The DTPA‐extractable soil Zn levels were very well correlated with Mehlich‐1‐extractable Zn. Mehlich‐3 extracted about 20% more soil Zn than Mehlich‐1, but Mehlich‐3 soil Zn was not as well correlated to Mehlich‐1 soil Zn as DTPA soil Zn. Lower pH solutions extracted more of the applied Zn, but more neutral solutions extracted Zn amounts which were better correlated with Zn uptake. On the other hand, Mehlich‐1, which had a lower pH, had better correlations with both applied Zn and leaf Zn than did Mehlich‐3. Shortening the DTPA extraction time to 30 minutes resulted in better correlations than the standard two hour extraction time. Chloride (Cl) was the best anion tested in relation to soil applied Zn recovery in combination with potassium (K), calcium (Ca), and aluminum (Al), and Cl optimized leaf Zn correlations for ammonium (NH4), K, Ca, and magnesium (Mg). The larger the valence of the cation, the better the correlation with applied Zn and the poorer the correlation with leaf Zn.

EVALUATION OF SOIL TESTS FOR ZINC IN SEMI ARID SOILS FOR MAIZE

A greenhouse experiment was conducted with 20 soils representing semiarid soils of Coimbatore district to peredict the most reliable soil test method for determining the available Zn status in the soil. Therewere four levels of Za (0, 2.5, 5.0 and 7.5 ppm) and cach treatment was replicated two times. Maize (Ganga 5) was used as the test crop and the crop was allowed to grow for seven weeks. The results showed that among the six extractants tried, EDTA + (NH4)2 CO3 and DTPA were found to be the most reliable soil test methods as compared to the other four methods employed. Between the two methods, DTPA soil test method could be recommended for determining the available Zn status in the soils of Coimbatore district as it had given higher relationship with the actual yield, Bray's per cent yield, Zn content in leaves and leaf sheath and stem

Predicting DTPA soil test zinc and associated rice response to applied zinc

Abstract The studies were conducted in field at 168 locations scattered throughout rice (Oryza sativa) growing tract of the Punjab with two plans of zinc (Zn) treatments along with nitrogen (N) and phosphorus (P)/N, P, and potassium (K) during 1991 and 1992. Effect of soil properties fpH, organic matter content (OM), and soil test P] on DTPA soil test Zn and associated rice (var. Basmati‐385) response was investigated. Applied as well as soil test Zn levels signified their importance in paddy yield improvement. However, soil properties (pH, OM, and soil test P) did not affect the rice response. DTPA soil test for Zn estimation was independent of these soil properties. A DTPA soil test Zn critical limit of 1.5 mg Zn/kg was obtained for rice by employing the Cate‐Nelson procedure.

Assessing the micronutrient requirement of winter wheat

Abstract Zinc, copper, iron and manganese requirement of wheat was assessed on loamy alluvial soils. Pot experiments were conducted to find out the relation of nutrient status of soil and plants to crop yields and to find out the extent of response due to foliar application of these nutrients. Sampling plant leaves at 40 days after sowing gave best indication of micronutrient status of the plants. The plants well supplied with these nutrients at this stage of the growing period supported best growth and produced maximum dry matter. Application of micronutrients as foliar spray later than 40 days after sowing also improved the dry matter production at 60 days in comparison to the basal application. This suggests that these micronutrients should be present in sufficient quantity during the early part of growth. Critical limits for soil DTPA‐ Cu, Zn, Fe, and Mn were 0.78, 0.8, 5.0, and 5.5 ppm, respectively. The critical tissue concentrations for Cu, Zn, Fe, and Mn were 8.0,22.0, 61.5 and 25 ppm, respectively.

The effectiveness of zinc fertilizers as measured by DTPA soil extractable zinc, dry matter production and zinc uptake by subterranean clover in relation to soil properties of a range of Australian soils

The effectiveness of zinc fertilizer (Zn) on a wide range of Australian soils was examined using subterranean clover (Trifolium subterranean cv. Nungarin) as a test crop in a glasshouse experiment. The initial effectiveness (IE) of zinc fertilizer as measured by dry matter production (DMP), and zinc content (uptake) of subterranean clover (clover) was found to vary markedly among the soil types. No simple linear retationship between the initial effectiveness measured by either dry matter production or uptake and any one soil property was found. IE values were found to be related to the pH (1 : 5 soil :water) (pHw) and the level of DTPA soil extractable zinc measured in the unfertilized soil (Zno). IE based on Zn uptake by clover tops was also related to the organic carbon (OC) (%) content of the soils. The model for IE measured by DMP in a stepwise linear regression was IEDMP = 2.682 - 0.107 pH,-4.852 Zn, (n = 45; r2 = 0-86). IE based on Zn uptake by clover tops was: IEuptake = 10.842 - 0.882 pH, - 0.310 OC (%) - 1.349 Zn, (n = 54; R2 = 0.85). The IE of zinc fertilizer measured by DTPA soil extraction (IEDTPA-zn) was also found to vary markedly among soil types. The level of zinc extracted by DTPA after the addition of Zn fertilizer was found to be affected by clay (%), organic carbon (%) and calcium carbonate (CaCO3) (%) content of the range of Australian soils. This relationship could be described by: IEDTPA - Zn = 0.178 + 0.0.002 Clay (%) + 0.014 OC (%) + 0.018 CaCO3 (%) (N = 54, r2 = 0.84)

Plant availability of Zn fractions in Saskatchewan soils

Two growth chamber experiments were conducted to assess the plant availability of Zn fractions in nine Saskatchewan soils. In one experiment, two rates of Zn (0, and 5 mg kg−1) were applied to navy beans grown on seven soils ranging in pH from 6.2 to 7.8. Most of the applied Zn was recovered in Pb-displaceable and Mn oxide associated fractions after a 7-d incubation. Growth of navy bean plants was normal in all soils and treatments. Dry matter yield did not respond to Zn application. The positive correlations between amounts of Zn in exchangeable, Pb-displaceable and acetic acid soluble fractions and plant uptake indicated the importance of these Zn fractions in influencing availability of Zn. The DTPA soil test was not a successful method for prairie soils with diverse soil properties on the basis of correlations. In the second experiment, three rates of Zn (0, 5 and 10 mg kg−1) were applied to alfalfa grown on two soils with pH of 5.5 and 7.9. The total dry matter yield of alfalfa grown on the calcareous soil was increased significantly by Zn application. No yield response to added Zn was observed in the acidic soil. In both soils, applied Zn increased the Zn concentration and total Zn uptake of alfalfa significantly over the control treatment. Changes in the distribution of applied and native Zn in different fractions before seeding and at second harvest suggest that Zn taken up by plants in the calcareous soil was from exchangeable, acid soluble and possibly residual Zn. Zinc uptake by plants grown on the acid soil was from exchangeable, Pb-displaceable, acid soluble and possibly from Mn oxide associated fractions. Key words: Zn fractions, plant availability, navy beans, alfalfa, pH

Use and Misuse of the DTPA Soil Test

AbstractThe DTPA soil test was originally developed to identify near‐neutral and calcareous soils with insufficient available Zn, Fe, Mn, and Cu for maximum yields of crops. It apparently draws on labile pools it was designed to extract and correlates well with plant micronutrient concentrations when the soil metal levels are neither too high nor too low. The soil test reliably reflects metal loadings to soils supplied in a variety of forms, but may not reliably predict plant metal concentrations expected from increased soil loadings. The successes or failures of the soil test noted in the literature can be explained as correct uses or misuses, respectively, of the test. The soil test is best used to identify micronutrient deficient, near‐neutral, and calcareous soils. Whenever one strays from the original design of the test, one should be aware of the possible consequences and pass that awareness on to others.

Effect of sulfur treatments on yield and uptake of Fe, Zn, and Mn by corn, sorghum, and soybeans

Abstract Iron chlorosis is widespread in corn, sorghum and soybeans growing in calcareous soils in Iran. A field experiment was conducted to investigate the effect of S treatments on yield and uptake of Fe, Mn and Zn by corn, sorghum and soybeans. Elemental S (powder sulfur) was incorporated into the soil before planting with the rates of zero, 100, 200 and 400 kg/ha. Results showed that elemental S decreased the soil pH and HCC3 ‐ concentration of soil extract, and increased soil DTPA‐ extractable Fe, Mn and Zn. Iron, and Zn uptake increased while Mn uptake decreased significantly by corn, sorghum and soybeans for almost all the treatments and Iron chlorosis was corrected. Yield increase over control was significant for sorghum and soybeans for all and every treatment. For corn, however yield showed signigicant increase over control only for 200 and 400 kg elemental S/ha. The results indicated that elemental S treatment was an effective means to alleviate iron chlorosis as well as to increase yield for c...

Long term availability of metals in sludge amended acid soils

Abstract Nicotiana tabacum L. was grown to maturity in 1984 at two research sites in Maryland which were amended with municipal sludge materials representing a variety of wastewater treatment technologies in 1972, 1976 and 1978. Four sludges from Washington, D.C. and Annapolis, MD were applied at rates equal to 0, 56, 112 and 224 Mg ha‐1. A high‐metal sludge from Chicago was applied at rates equal to 50 and 100 Mg ha‐1 in 1978. Composite leaf samples of cured tobacco and Ap horizon soil samples were analyzed for Zn, Cu, Mn, Fe, Pb, Ni and Cd. Available soil metals were estimated using three procedures: DTPA (pH 7.3), Double Acid and Mehlich 3. DTPA and Double Acid produced significant correlation coefficients (r) for Zn, Cu, Mn, Ni and Cd when compared with plant metal contents; however, none of the extractants produced significant r values for Fe or Pb. All sludge sources resulted in significant increases in DTPA soil Zn, Cu, Ni and Cd with increased application rates; however, plant levels were affected...

Prediction of Available Zinc in Sewage Sludge‐amended Soils

AbstractA routine soil test would be helpful for management of agricultural soils amended with sewage sludge high in Zn. Fourteen field sites were selected in the Coastal Plain, Piedmont, and Ridge and Valley regions of Virginia to evaluate the suitability of the dilute HCl‐H2SO4 and DTPA soil extractants for prediction of Zn uptake by corn (Zea mays L.). Soil and corn tissue samples were collected from these sites where sewage sludge had been applied previously. Multiple regression analysis was used to assess the forms of soil Zn extracted by dilute HCl‐H2SO4 and DTPA. The exchangeable and specifically sorbed, organically bound and noncrystalline hydroxide and oxide bound Zn fractions were tested to develop equations. Dilute HCl‐H2SO4 extracts were related to the three Zn fractions (R2 = 0.98**), whereas organically bound Zn was the only Zn fraction related to DTPA‐extractable Zn (r = 0.96**). Earleaf Zn concentration correlated more closely with DTPA‐extractable Zn (r = 0.64*) than with dilute HCl‐H2SO4‐extractable Zn (r = 0.35). The earleaf Zn concentration was studied as a function of either DTPA‐ or dilute HCl‐H2SO4‐extractable Zn, exchangeable and specifically sorbed Zn, organically bound Zn, and noncrystalline hydroxide and oxide bound Zn. Inclusion of the above fractions in a multiple regression analysis did not improve the relationship between earleaf Zn concentration and dilute HCl‐H2SO4‐extractable Zn. A coefficient of multiple determination (R2 = 0.77**) was obtained between earleaf Zn concentration and a two variable regression equation comprised of DTPA‐extractable Zn and organically bound Zn. The negative regression coefficient for organically bound Zn indicated that a portion of this fraction, which was extracted by the DTPA, did not supply Zn to corn plants.

Correlation of DTPA extractable Fe with indigenous properties of selected calcareous soils

Abstract During the past few years the DTPA soil test (Lindsay and Norvell, 1978) has been widely accepted for the routine estimation of plant available Fe. The strength of the DTPA test lies in the ability of DTPA to extract labile forms of Fe from the soil, as the plant is able to extract these same labile Fe forms. The objective of this study was to determine the most probable sources of labile Fe which are being removed by the DTPA extractant. Twenty‐four calcareous soils of Texas were extensively analyzed with respect to Fe oxide, organic matter, clay and solution phases. DTPA extractable Fe was highly correlated with ammonium oxalate extractable Fe (amorphous or poorly crystalline Fe oxide), but not with citrate‐dithionite extractable Fe (total free Fe oxide, including well‐crystalline forms), indicating that the amorphous phase was more readily solubilized by DTPA. Clay content and organic carbon parameters were also correlated (though somewhat less) with DTPA‐extractable Fe. It is likely that the ...

Comparison of statistical methods for separating iron deficient from sufficient soils

Abstract Two correlation data sets for the DTPA soil test and one for the NH4HCO3‐DTPA soil test were used to evaluate various soil test correlation methods. Visual, graphical, Mitscherlich, Chi‐square, optimum predictive value, and two‐ and three‐class analysis of variance methods were compared. Critical levels were identified for each method and transition or marginal zones were determined for those methods which facilitate their identification. Critical levels ranged from 3.5 to 5.0 ppm NH4HCO3‐DTPA extractable iron and from 3.5 to 4.8 ppm DTPA extractable iron. Generally, transitional zones were very similar for all methods with both soil tests. Based on these results the Chi‐square method, supported by visual and/or graphical methods, is recommended because of their simplicity and ability to identify transition or marginal zones.