Suitability of Different Soil Extractants for Determination of Available Cu and Mn Contents in Polish Soils

The aim of this study was to compare four micronutrient soil-test extractants currently in common use in Poland, Rinkis, Mehlich 3, modified Lindsay and Norvell, and Yanai, for ability to determine the plant-available concentration of copper (Cu) and manganese (Mn) in two acidic soils (pH 4.8–4.9) that had been amended with different doses of Cu and Mn fertilizers. The comparison was based on two pot experiments (each with a different soil) with corn (Zea mays), barley (Hordeum vulgare), spring wheat (Triticum aestivum), rape (Brassica napus), red clover (Trifolium pratense), and English ryegrass (Lolium perenne). The extractants were evaluated based on a correlation analysis of the microelement concentrations in plants at the end of the vegetative phase and micronutrient concentration in the fertilized soil determined by each extractant at the end of the experimental period. The largest extractable concentrations of Cu and Mn in soils were obtained with Rinkis. The modified Lindsay and Norvell soil test extracted the lowest amount of both microelements. For soil Cu, the results with the Mehlich 3 and Yanai extractants were highly correlated with the Rinkis procedure results (r = 0.98). The modified Lindsay and Norvell results were not as well correlated with Rinkis (r = 0.84). For soil Mn, the correlation of results of Yanai, Mehlich 3, and modified Lindsay and Norvell to Rinkis ranged from r = 0.80 to r = 0.86. Levels of Mn and Cu measured with each of the extractants were highly correlated with plant tissue concentrations of Mn and Cu in most of the six plant species. The exceptions to this were the following: The modified Lindsay and Norvell soil Cu levels were not correlated with ryegrass and wheat plant Cu levels; Mehlich 3 Cu was not correlated with red clover Cu; and the Rinkis-extractable Mn was not correlated with the wheat Mn. It is concluded that the Yanai and Mehlich 3 procedures are suitable alternatives to the Rinkis for Cu but not for Mn.     

Development of a New Soil Extractant for Simultaneous Phosphorus,Ammonium, and Nitrate Analysis

Abstract

A new soil extractant (H³A) with the ability to extract NH₄, NO₃, and P from soil was developed and tested against 32 soils, which varied greatly in clay content, organic carbon (C), and soil pH. The extractant (H³A) eliminates the need for separate phosphorus (P) extractants for acid and calcareous soils and maintains the extract pH, on average, within one unit of the soil pH. The extractant is composed of organic root exudates, lithium citrate, and two synthetic chelators (DTPA, EDTA). The new soil extractant was tested against Mehlich 3, Olsen, and water for extractable P, and 1 M KCl and water‐extractable NH₄ and NO₂/NO₃. The pH of the extractant after adding soil, shaking, and filtration was measured for each soil sample (5 extractants×2 reps×32 soils=320 samples) and was shown to be highly influential on extractable P but has no effect on extractable NH₄ or NO₂/NO₃. H³A was highly correlated with soil‐extractable inorganic N (NH₄, NO₂/NO₃) from both water (r=0.98) and 1 M KCl (r=0.97), as well as being significantly correlated with water (r=0.71), Mehlich 3 (r=0.83), and Olsen (r=0.84) for extractable P.     

Comparison of extractable phosphorus from two sulfuric acid methods with the Mehlich phosphorus test number one

Abstract

All mineral phosphates in soil dissolve more completely when HCl is mixed with H₂SO₄ than with the HCl alone. It was hypothesized that a new extracting solution of H₂SO₄ alone with the same ionic strength or the same acidity as the Mehlich P1 extractant would extract similar amounts of soil phosphorus (P) as the Mehlich P1 soil test. Thirty six acid soils from Alabama, Georgia, North Carolina, South Carolina, and Colorado were used in this study. These acid soils reflect wide ranges in parent materials, texture, pH, organic matter, and available soil P. They were analyzed for available soil P with the Mehlich P1 soil test and with the two H₂SO₄ methods: Method A has an extracting solution of same ionic strength (0.0875M) as the Mehlich P1 extractant, and Method B was an extracting solution of the same acidity (0.0375M) as the Mehlich P1 extractant. Correlations between the results of Mehlich P1 with Method A and Method B were 0.994 and 0.997, respectively. The measured test precision was <3.5% for all three methods. The new H₂SO₄ methods are simple and faster to conduct under routine operations than the original Mehlich P1 extractant, and because of the high correlations, the H₂SO₄ methods should predict crop response to P as well as the original Mehlich P1 extractant for acid soils.     

Effect of Grinding on Soil Extraction by Aqua Regia, 2 M Nitric Acid,and Mehlich 3

Abstract

The effect of grinding on soil extraction was determined for two soil fractions and three extractants. Arsenic (As), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn) were extracted by aqua regia and 2 M nitric acid. Mehlich 3 extractant was used for determination of potassium (K), magnesium (Mg), calcium (Ca), phosphorus (P), iron (Fe), and aluminum (Al). One hundred forty‐seven agricultural soil samples representing all major soil types, climatic regions, and proportions of agronomic cultures in the Czech Republic were collected for the study. Particle size fractions smaller than 2 mm and smaller than 0.150 mm were chosen for investigation. Extraction of elements by aqua regia was similar for both size fractions of soil. Cold 2 M nitric acid is a weaker extractant than aqua regia, and a statistically significant increase in extractable Be (5%), Cd (6%), Co (11%), Cu (5%), Ni (5%), and V (2%) was measured with the finely ground soils. An increase for the finer fraction for K (10%) and Mn (25%) was found for Mehlich 3. A more complex nonlinear relationship was found for Mehlich 3 extractable Al and Fe. This was probably caused by a more intensive re‐adsorption of Fe and Al to the finely ground soils.     

Factors Affecting Mehlich III Soil Test Methodology for Extractable P

Agronomic and environmental testing laboratories in Texas and elsewhere have adopted Mehlich III (M3) as their official soil test phosphorus (P) methodology. However, M3-P data could be skewed due to non-homogenous soil samples or failure to follow standard protocol which could influence recommendations or restrictions. Twelve agricultural soils with a wide range of properties were collected from across Texas. Exhaustive efforts via multiple methods were made to prepare homogeneous representative soil samples. The standard M3 protocol selected was a 2 g weighed soil sample placed in a 148 ml disposable plastic cup, using a 1:10 soil:M3 solution ratio, shaken on a 200 rpm orbital shaker with a 2.5 cm throw for exactly 5 min, and filtered through Whatman No. 2 filter paper. The standard protocol was compared with nine different protocol variations with variables including soil weighing versus scooping, scooping repeatability of different technicians, soil sample weight, shaking type, speed and time, different filter papers, and varying soil:extractant ratios. Extent of soil pulverization on M3-P results was also evaluated. Tests were performed in four replications for all protocols to assess effects on M3-extractable soil P. Percent recovery of soil during grinding had no effect on M3-extractable P. Little difference in M3-extractable P was observed between scooping and weighing of 2 g soil samples. Shaker type had no effect on extractable P in soils with low clay contents, however, increasing shaking speed and using an orbital shaker resulted in higher extractable P, especially in clayey soils. Both Whatman No. 1 and 2 filter papers were found suitable for M3-P analyses. Different soil:extractant ratios resulted in a highly significant influence on the amount of M3-P extracted. However, when ratios were maintained between 1:9 and 1:11, few differences in extractable P were observed. Using sample weights below 3 g did not significantly alter precision or accuracy of results. However, technician variation in scooping of 2 or 5 g soil samples resulted in significant differences in M3-P.     

Evaluation of four chemical extractants for metal determinations in wetland soils

Abstract

Wetland soils (hydric soils) are unique in their chemical characteristics compared to upland soils. It is known that they are capable of removing a variety of wastes from polluted water entering the wetland including metals and potentially toxic heavy metals. When these metals are determined in wetland soils, it is necessary to use the proper chemical extractant(s). Four commonly used chemical extractants (Mehlich 1, Mehlich 3, 0.1M HCl, and DTPA) for soil fertility evaluation were selected to measure metal concentrations of three different wetland soils/spoils. Soil samples were collected from the constructed wetland cells which were lined with Abernathy silt loam topsoil and two different mine spoil materials [collected from active coal strip‐mined sites in Alabama (pH 5.9) and Tennessee (pH 3.2)]. Mehlich 3 extracted the most zinc (Zn), iron (Fe), manganese (Mn), calcium (Ca), magnesium (Mg), potassium (K), sodiumm (Na), and aluminum (Al), while 0.1M HC1 extracted more cadmium (Cd), copper (Cu), and lead (Pb). Extractants followed the same trend in removing quantities of the metals from the three soil/spoil materials, with DTPA generally extracting the least amount of the metal (the trend was Mehlich 3 > 0.1N HCl > Mehlich 1 > DTPA). However, DTPA removed larger quantities of metals from Tennessee spoil compared to Alabama spoil and topsoil, suggesting the higher effectiveness of DTPA under acidic conditions. Metal concentrations in plant tissue did not show a definite trend in correlation with metals extracted by the four chemical extractants.     

Evaluation of Mehlich 3 extractant for estimating phosphorus deficiency and phosphorus sorption of Zimbabwean soils

Abstract

The Mehlich 3 extractant was compared with the resin method for its ability to predict the phosphorus (P) status of Zimbabwean soils. Correlation of P extraction between the two methods and with plant growth was found to vary with soil texture. Because the Mehlich 3 extractant was less influenced by texture, it was better able to predict the P status over a wide range of soil types. The Mehlich 3 extractant correctly predicted P deficiency for all Zimbabwean soils, except for those that contained visible calcium carbonate. Mehlich 3‐extractable aluminum (Al) was very highly correlated with the maximum P‐sorption capacity of a wide range of soils, excluding those with calcium carbonate. Adoption of the Mehlich 3 extractant for multiple elemental analysis of soils in Zimbabwe is recommended, particularly if routine Al measurement is included as an indicator of soil P requirements.     

Appraisal of Some Soil Tests for Zinc Availability to Late‐Sown Wheat Grown in Mollisols

Abstract

Five soil extractants, namely, 0.005 M diethylene triamine pentaacetic acid (DTPA) (pH 7.3), 0.005 M DTPA+1 M ammonium bicarbonate (pH 7.6), Mehlich 3, 0.01 M ethylene diamine tetraacetic acid (EDTA)+0.05 M ammonium carbonate (pH 8.6), and 1 M magnesium chloride (MgCl₂) (pH 6.0), were evaluated to predict the response of wheat to zinc (Zn) application in Mollisols. These extractants could be arranged in the following decreasing order of their Zn extracting power: Mehlich 3>0.005 M DTPA+1 M ammonium bicarbonate>0.01 M EDTA+0.05 M ammonium carbonate>0.005 M DTPA>1 M MgCl₂. The critical limits of Zn in soil, below which the yield response to late sown wheat (var. UP‐2338) to Zn application could be expected, were 0.57 mg 0.005 M DTPA (pH 7.3) extractable and 1.72 mg Mehlich 3–extractable Zn kg^?1 soil. The critical limit of Zn in whole shoot at 60 days after emergence was found to be 26.1 mg Zn kg^?1 plant tissue. The DTPA and Mehlich 3–extractable soil Zn also correlated significantly and positively with Zn concentration in whole shoot at 60 days after emergence and total Zn uptake by wheat at harvest.     

A comparison of Mehlich I and Mehlich III extractants as predictors of manganese,copper and zinc availability in four Delaware soils

Abstract

The relative effectiveness of Mehlich I (.025N H₂SO₄ + .05N HCl) and Mehlich III (0.2N CH₃COOH + 0.25N NH₄NO₃ +.015N NH₄F + .013N HNO₃ + .001M EDTA) extractants as predictors of Mn, Cu and Zn uptake was assessed in a greenhouse experiment with four Delaware soils. The soils were adjusted to eight pH levels by addition of Ca(OH)₂ or elemental S, and received comparable amounts of Mn, Cu and Zn as either (1) MnSO₄ + CuSO₄ + ZnSO₄ or (2) Poultry Manure. Mehlich 1 and III extractable Mn and Zn, but not Cu, were well correlated in most instances. Excellent correlations were obtained between Mn uptake and Mehlich I and Mehlich III extractable Mn, for all soils and sources. In general, however, neither Zn nor Cu was found to correlate well with plant uptake. Based on this study, conversion to Mehlich III, as a routine soil test extractant for micronutrients, would not result in a significant improvement over the currently used Mehlich I extractant.     

Evaluation of certain Ni soil tests for an initial estimation of Ni sufficiency critical levels

Although Ni is officially recognized as an essential micronutrient for all higher plants, the majority of the published research on soil availability of Ni focuses on its hazardous role as a heavy metal. The objective of the study was to evaluate certain Ni soil tests in uncontaminated soils for an initial estimation of its sufficiency critical levels. Nickel was extracted from 30 cultivated soils employing the following extraction methods: DTPA, AB‐DTPA, AAAc‐EDTA, Mehlich‐3, 0.1 M HCl, and 0.1 M HNO₃. Ryegrass (Lolium perenne L.) was grown in pots containing the soils, harvested five times, certain plant parameters were determined, and the Cate–Nelson procedures were used for Ni critical levels determination. Among the six methods, HCl was the least reliable extractant for the evaluation of soil available Ni, whereas the most significant (p ≤ 5%) relationships between Ni concentration or Ni uptake by ryegrass and Ni soil tests were consistently obtained for AAAc‐EDTA or Mehlich‐3 extractable Ni. In many cases, > 80% of the variability of Ni concentration or uptake by ryegrass was explained by these two soil tests without the inclusion of other soil properties that affect Ni bioavailability. Sufficiency critical levels of Ni in soil were ≈ 2 mg kg^–1 for both methods. Consequently, as an initial approach, concentrations of AAAc‐EDTA or Mehlich‐3 extractable Ni < 2 mg kg^–1 are probably a good guide to indicate soils that will respond to Ni fertilization.     

Effect of Liming on the Plant Availability and Distribution of Zinc and Copper among Soil Fractions

Abstract

Information on the redistribution of applied micronutrients into different fractions as a result of lime application is important to predict plant accumulation of nutrients and to select appropriate chemical extraction procedures for evaluation of micronutrient availability. The present work was carried out to study the influence of liming on the availability and redistribution of zinc (Zn) and copper (Cu) among soil fractions. Additionally, the effect of liming was evaluated on the recovery of these micronutrients by different chemical extractants (Mehlich‐1, Mehlich‐3, and diethylenetriaminepentaacetate (DTPA), which were correlated with Zn and Cu concentrations in corn (Zea mays L.) plants and soil fractions (exchangeable, organic matter, amorphous iron oxides, and crystalline iron oxides). The results showed that Zn added to soil samples that did not receive lime was retained mainly in the exchangeable and organic matter fractions. The liming resulted in distribution of Zn into iron oxides and as a result decreased the plant accumulation of Zn. Mehlich‐3 was the most efficient extractant to predict the plant accumulation of Zn in the acid soils, whereas DTPA was the most efficient in the limed soils. The oxide crystalline fraction was the major fraction responsible for retaining Cu in the soils. However, Cu added to soil was distributed mainly into organic matter. Mehlich‐3 was the most suitable extractant for predicting the bioavailability of Cu in limed or unlimed soils.     

Evaluation of Agro Services International Soil Test Method for Phosphorus and Potassium

Soil testing is widely adopted as an essential diagnostic tool for identifying soil nutrient factors that limit sustained crop production. A systematic approach for rapid soil testing and fertilizer recommendation has been introduced and widely used in China by Agro Services International (ASI), USA. To verify the usefulness and reliability of the ASI method in soil testing and fertilizer recommendation in comparison with other commonly used traditional soil testing methods, 294 soil samples from major agricultural regions and soil types in China with a wide range of soil pH, from 5.1 to 8.9, were taken and analyzed for available phosphorus (P) and potassium (K) by the ASI multielement extraction solution and selected traditional methods, Olsen extractant for P, ammonium acetate (NH₄OAc) extractant for K, and multielement extractant Mehlich 3 for P and K. Also, 46 soils were selected from northern China regions for a greenhouse trial with sorghum seedlings to determine if the soil testing values correlate well with plant response. Results indicated that the amount of soil P extracted by the ASI method (ASI P) was correlated to both soil extractable P tested by the Olsen extractant (Olsen P) and Mehlich 3 extractant (Mehlich 3 P). The correlation coefficient of ASI P with Mehlich 3 P (R² = 0.86) was greater than that of ASI P with Olsen P (R² = 0.74) across all selected soils. A good correlation was also found between the exchangeable K from the ASI method with the traditional ammonium acetate method (R² = 0.81) and the Mehlich 3 method (R² = 0.85). The results from the greenhouse trial showed that the extractable P and exchangeable K by the ASI multielement extraction solution could be used to represent the fertility status of soil P and K for the selected soils. Regression analysis indicated that the relative dry-matter yield of the sorghum plants can be predicted with either ASI P and ASI K values with the correlation coefficients (R²) values of 0.78 and 0.72 respectively and could be a good measure for soil testing and fertilizer recommendation in the selected soils and regions in China.     

Evaluation of Universal Extractants for Determination of Some Macronutrients from Soil

Evaluation of nutrient status in soil is important for nutritional, environmental, and economical aspects. The objective of this work was to find out the most suitable universal extractant for determination of available phosphorus (P) and nitrate (NO₃-) and exchangeable potassium (K), calcium (Ca), and magnesium (Mg) from soils using 0.01 M calcium chloride (CaCl₂), 0.01 M barium chloride (BaCl₂), 0.1 M BaCl₂, 0.02 M strontium chloride (SrCl₂), Mehlich 3, and ammonium bicarbonate diethylene triamine penta acetic acid (AB-DTPA) extractants. Composite surface soil samples (0–20 cm) were collected from the Eastern Harage Zone (Babile and Haramaya Districts), Wolaita Zone (Damot Sore, Boloso Bombe, Damot Pulasa, and Humbo Districts), and Dire Dawa Administrative Council by purposive sampling. The experiment was carried out in a completely randomized design (CRD) with three replications. Results indicated that the greatest correlations were found between Mehlich 3 and Olsen method and also between 0.02 M SrCl₂ and Olsen method for available P. The amount of NO₃^– extracted by 0.02 M SrCl₂ was significantly correlated to the amount determined by 0.5 M potassium sulfate (K₂SO₄). The amounts of exchangeable K, Ca, and Mg determined by ammonium acetate (NH₄OAc) method were significantly correlated to the amount determined by universal extractants tested. In general, both 0.02 M SrCl₂ and Mehlich 3 can serve as universal extractants for the macronutrients considered in this study with the former being more economical when NO₃^– is included.     

Evaluation of Mehlich 3 for Extraction of Copper and Zinc from Irish Grassland Soils and for Prediction of Herbage Content

Abstract: The objective of this study was to determine how the extractant Mehlich 3 (M3) compared with other methods currently used in Ireland for determination of copper (Cu) and zinc (Zn) in soils. Samples from eight different mineral soil types, four of sandstone/shale and four of limestone origin, were analyzed for copper and zinc using M3 and conventional extractants. Herbage samples were taken from the soils and analyzed for Cu and Zn. Mehlich 3 results showed good correlation with ethylenediamine‐tetraacetic acid (EDTA)– and diethylenetriamine‐pentaacetic acid (DTPA)–extractable Cu and Zn. Inclusion of soil properties in multiple regression models improved the coefficients of determination. All extractants were equal in their ability to predict Cu and Zn herbage content. Differences between sandstone/shale and limestone soils in relation to herbage content were also found, with the better relationship found in sandstone/shale soils.     

Mehlich‐1‐ and DTPA‐extractable lead in soils in relation to soil properties

Abstract

Mehlich‐1 and DTPA extractants are frequently used to predict metal availability in soils. Metal extractability by the acid or chelate extractant reflects the metal characteristics and metal‐soil interactions. In this study, samples of eight topsoils from the southeastern United States were incubated with added lead (Pb) at the rate of 40 mg#lbkg^‐1. After five months in the greenhouse, Mehlich‐1 and DTPA extractants were employed to extract Pb in both metal‐amended and natural soils. For the natural soils, Pb concentration in the DTPA extractant was always higher than that in the Mehlich‐1 extractant. This indicates that the DTPA chelate extractant is able to dissolve some Pb in soils which is not solubilized by protons. The negative correlation found between Mehlich‐1‐extractable Pb and soil clay content might result from two mechanisms: i) strong association between Pb and soil surfaces, or ii) readsorption of Pb during extraction. None of the correlations between DTPA‐extractable Pb and soil properties was significant, suggesting that the DTPA‐extractable Pb is not heavily dependent on soil properties. The DTPA extractant showed a high ability to solubilize Pb in the natural soils possibly due to a high affinity of Pb for soil organic matter.     

Comparisons of phosphorus availability between anion exchange resin and mehlich‐1 extractions among Oxisols with different capacity factors

Abstract

Acid and dilute‐salt chemical extractants are commonly used to assess and adjust phosphorus (P) availability in soils. Soybean was grown for 45 days under greenhouse conditions on samples of 10 Oxisols treated with variable levels of soluble P to compare critical soil P levels between an anion exchange resin (AER) and the Mehlich‐1 extractant, and to evaluate the influence of the soil P capacity factor (PCF) on the critical soil P levels. Variation among soils in the quantities of extracted P and critical P levels with the AER was less than that with Mehlich‐1. Low correlation values between soil characteristics related to PCF and measurements of AER soil P suggested that the AER method was not as sensitive to variations in soil PCF as Mehlich‐1. Interpretations of AER critical P levels, therefore, do not need auxiliary measures of PCF as with the Mehlich‐1 extractant. The reverse was true, however, for P uptake. Therefore, the criteria used to assess plant response to P (P uptake or dry matter production) in soils with variable PCF will influence the results obtained in correlations between methods used to extract soil P.     

Evaluation of universal extractants for determining plant available potassium in intensively cultivated soils

Abstract

Eighteen soils from northwestern Switzerland were used to study the value of seven universal extractants (CaCl₂; DB‐DTPA; Mehlich 1, 2, and 3; Morgan‐Wolf; and NH₄OAc‐EDTA) for predicting plant available potassium (K) as compared to a bioassay (a modified Neubauer test with winter rye). These extractants were evaluated on the basis of K uptake by the bioassay test and the soil K status. In order to create the sufficiency level of exchangeable K for plant growth, soils were treated with 0, 20, 40, 80, and 160 mg K/kg of soil. The range of K uptake by the bioassay tests was between 89.2 and 403.0 mg/kg of soil for the control pots, and 136.6 to 495.8 for the K treatments with optimal conditions for plant growth. The average amounts of K extracted by the seven universal extractants, in ascending order, were: CaCl₂ < Morgan‐Wolf < Mehlich 1 < Mehlich 2 < NH₄OAc‐EDTA < Mehlich 3 < DB‐DTPA. The highest simple correlation with K uptake versus the bioassay test was obtained with the DB‐DTPA (r = 0.89) extractant and the lowest with the Mehlich 1 (r = 0.53) extractant. The DP‐DTPA, NH₄OAc‐EDTA and Mehlich 3‐K procedures showed an advantage over K procedures based on water soluble and exchangeable K pools in the investigated soils in order to predict the amount of plant‐available K. A simple regression and the Cate‐Nelson graphic method offer the possibility of assessing the soil‐K status using K values obtained by these universal extractants and to calibrate them against K forms as follows: exchangeable, water soluble, and non‐exchangeable.     

Comparison of Three Micronutrient Soil-Test Extractants in Three Greek Soil Types

The purpose of the present study was to compare the ability of three micronutrient soil-test extractants [diethylenetriaminepentaacetic acid (DTPA), Mehlich 3, and Soltanpour and Schwab] to determine plant-available concentrations of manganese (Mn), iron (Fe), and zinc (Zn) in three soils (from parent material Marl, Gneiss schist, and Peridotite) from central Macedonia, northern Greece. In black plastic bags containing 3 kg of air-dried soil, self-rooted olive plants (cv. Chondrolia Chalkidikis) were grown for about 5 months and irrigated with distilled water during the experimental period. At the end of the experimental period, the three extractants were evaluated, based on correlation analysis among leaf micronutrient concentrations, total plant micronutrient content of olive plants, and soil micronutrient concentrations determined by each extractant. The largest extractable concentrations of Mn, Fe, and Zn were determined by Mehlich 3, compared to the other two soil-test extractants. However, for the correlation analysis, the greatest correlation coefficient between leaf Mn (and total plant Mn content) and soil extractable Mn was achieved when DTPA was used (varying from 0.76 to 0.88, depending on soil type). Therefore, it is concluded that DTPA was a better extractant to determine plant-available Mn than the other extractants for the three soils studied. For correlations between leaf Fe and Zn concentrations and also for total plant Fe and Zn content, and soil extractable concentrations, the type of extractant and soil type play a very important role in determining the best correlation. This means that in each soil type the greatest correlation was achieved with the use of other extractant. For example, for Fe in the Marl and Peridotite soils the best correlation was found for Mehlich 3, whereas in the Gneiss schist the best correlation was achieved for DTPA (R = 0.72–0.94). For Zn, in the Gneiss schist soil the best extractant in determining plant available concentration was Soltanpour and Schwab (R = 0.49–0.60), whereas in the other two soil types DTPA was found to be the most reliable extractant (R = 0.51–0.78). Therefore, soil type should be carefully and thoroughly studied by the researchers in similar future experiments.     

Mehlich 3 Extraction of Boron in Boron Treated Soils as Compared to Other Extractants

Abstract

Hot water extraction (HW) is time‐consuming, highly variable, and losing popularity as the standard method for estimating plant‐available boron (B) in soil. Proposed alternatives are not widely used and guesstimation is replacing assessment at many soil test facilities. Mehlich 3 is increasingly promoted as a universal extractant, and diethylenetriaminepentaacetic acid (DTPA)–sorbitol and pressurized hot water (PHW) are effective and comparable to hot water extraction but also simpler and easier. Mehlich 3 B extraction has been compared mainly to hot water extraction. Because Mehlich 3 usage would be limited to neutral to acid soils, this study used a limed acid Darco loamy fine sand (loamy, siliceous, semiactive, thermic Grossarenic Paleudult) from eastern Texas to which 10 rates of B were applied followed by either incubation without plants or planting to alfalfa in greenhouse pots. Mehlich 3 extraction of soils obtained from a long‐term experiment on Darco soil from which alfalfa yield response has already been related to hot water, DTPA–sorbitol, and PHW is reported. The purpose was to determine the efficiency of Mehlich 3 B extraction compared to hot water, PHW, and DTPA–sorbitol in these B‐fertilized soils. Mehlich 3–extractable B significantly correlated with the rate of B application to incubation, greenhouse, and field soils and with B concentration and total B uptake in alfalfa in a greenhouse experiment. However, yield responses to B application were not observed in the greenhouse study. In the field where B response to B application was observed, Mehlich 3–extractable B did not correlate with alfalfa yield, whereas hot water and pressurized hot water did. In considering Mehlich 3 for B extraction, be aware that some older inductively coupled plasma (ICP) models may have significant drift when B is measured in Mehlich 3 extractant. In the current study, this problem was overcome with a new model instrument. Although effective in estimating B levels imposed on soils by fertilizer application, Mehlich 3 could not predict yield and thus cannot currently be recommended as a “universal” extractant to include B.     

Comparison of mehlich 1 and mehlich 3 extractants for P,K, Ca,Mg, Mn,Cu and Zn in atlantic coastal plain soils

Abstract

The Mehlich 3 (M3) extractant was introduced in 1981 to improve the efficiency of soil testing laboratories by eliminating the need for multiple extractants for P, K, Ca, Mg, Mn, Cu and Zn. The M3 was also intended to be suitable for a wide range of soils, perhaps to serve as a “universal”; soil test extractant. At present, regional soil testing committees throughout the U.S. are investigating the M3 in this regard.

Development of a field calibration data base for a new soil testing extractant is an essential, but expensive and time‐consuming process. An interim measure is the use of conversion equations between new and current extractant(s). These equations allow for use of the new extractant with existing field calibration data. The objectives of this study were (i) to develop conversion equations for the Mehlich 1 (M1) and M3 extractants for Atlantic Coastal Plain soils, and (ii) to determine the influence of soil pH and organic matter content on the relative extractability of P, K, Ca, Mg, Mn and Zn by Ml and M3.

Four hundred soil samples, obtained from field plots and commercial crop samples submitted to the University of Delaware Soil Testing Laboratory were analyzed for P, K, Ca, Mg, Mn, Cu and Zn by M1 and M3. Highly significant correlations between M3 and M1 were found for all nutrients (r=0.92*** to 0.97***) and, except for Cu and Mn, soil pH and OM did not markedly improve the linear regression equations developed for conversion between M3 and M1. Inclusion of OM in a multiple regression equation between M3 and M1 extractable Cu increased R² from 0.46** to 0.71***; R² for Mn+(pH+OM) was 0.48***, relative to 0.35*** for extractable Mn alone. Critical values for M3 P, K, Ca, and Mg, based on conversion equations restricted to soils testing less than high with the M1 extractant, were 41, 49, 295 and 45 mg.dm^‐3, respectively. For Mn and Zn, at a pH of 6.2, M3 critical values were 9.5 and 0.6 mg.dm^‐3, while for Cu, the M3 critical value ranged from 0.5 to 1.1 mgdm^‐3 for soil OM of 2 to 8%.