Mehlich 3 Research Articles

Simultaneous multielement extraction with the Mehlich-1 solution for Southern Brazilian soils determined by ICP-OES and the effects on the nutrients recommendations to crops

The amounts of macro (P, K, Ca and Mg) and micronutrients (Cu and Zn) extracted with the Mehlich-1 (M1) solution, by the 1.0 mol L-1 KCl (KCl) and with the 0.1 mol L-1 HCl (HCl) for representative soil types of the Rio Grande do Sul state (Brazil) were compared with those extracted with the Mehlich-1 solution determined with the inductively coupled plasma optical emission spectroscopy (ICP). The amounts of nutrients extracted by the different methods showed high correlation coefficients. On average, the Mehlich-1 solution extracted similar amounts of P, determined with colorimetric and ICP methods, and, K determined with emission and ICP. The amounts of Ca and Mg extracted with the Mehlich-1 solution, determined by ICP, were similar to those extracted with the KCl solution determined by the atomic absorption spectrophotometry. The amounts of Cu and Zn extracted with the Mehlich-1 solution, determined by the ICP, were higher than those extracted with the 0.1 mol L-1 HCl determined by the atomic absorption spectrophotometry. The results indicate that the Mehlich-1 solution and ICP can be used for simultaneous multielement extraction and determination for Southern Brazilian soils. However, a conversion factor for values interpretation is needed. The use of the conversion factor to determine the K availability index in soils is adequate and does not affect the K recommendations for crops in southern Brazilian soils.

Effect of Application of Chromium Feedstock Compost on the Growth and Bioavailability of Some Trace Elements in Lettuce

A pot experiment was conducted to investigate the effect of chromium compost (0, 10, 30, and 50%) on the growth and the concentrations of some trace elements in lettuce (Lactuca sativa L.) and in the amended soils. Compost addition to the soil (up to 30%) increased dry matter yield (DMY); more than 30% decreased DMY slightly. The application of compost increased soil pH; nitric acid (HNO3)–extractable copper (Cu), chromium (Cr), lead (Pb), and zinc (Zn); and diethylenetriaminepentaacetic acid (DTPA)–, Mehlich 3 (M3)–, and ammonium acetate (AAc)–extractable soil Cr and Zn. The addition of Cr compost to the soil increased tissue Cr and Zn but did not alter tissue cadmium (Cd), Cu, iron (Fe), manganese (Mn), nickel (Ni), and Pb. The Cr content in the lettuce tissue reached 5.6 mg kg−1 in the 50% compost (326 mg kg−1) treatment, which is less than the toxic level in plants. Our results imply that compost with high Cr could be used safely as a soil conditioner to agricultural crops.

Interlaboratory Validation of the Mehlich 3 Method as a Universal Extractant for Plant Nutrients

The Mehlich 3 (M3) method is widely used to extract plant-available phosphorus from soil over a wide range of pH values. The method is also used by many laboratories to determine multiple plant-available nutrients simultaneously. However, except for P, this method has not been statistically validated within and among laboratories. The objective of this study was to determine the repeatability (within-laboratory performance) and reproducibility (among-laboratories performance) of the M3 method for several different nutrients by using a wide variety of soils. An in-house homogeneity test was conducted for 11 soils. Three replicates of each of the 11 soils were sent to 23 domestic and international laboratories for analyses primarily for K, Ca, Mg, Zn, Mn, Fe, and Cu. Samples were scooped, weighed, or both scooped and weighed for extraction. The various nutrients in the extracts were quantified by the participating laboratories by using inductively coupled plasma-atomic emission spectrometry. Ranges (in parentheses) of the repeatability relative standard deviation (RSDr) values for the scooped samples were K (3.88-6.14%), Ca (2.19-10.6%), Mg (2.27-5.73%), Zn (4.11-42.7%), Mn (3.15-8.53%), Fe (2.32-7.74%), and Cu (3.65-11.2%). For the weighed samples, the ranges (in parentheses) of the RSDr values were K (1.65-4.65%), Ca (1.43-16.9%), Mg (1.37-9.83%), Zn (2.60-33.0%), Mn (1.61-4.90%), Fe (1.56-4.47%), and Cu (2.95-17.9%). Ranges (in parentheses) of the reproducibility relative standard deviation (RSDR) values for the scooped samples were K (7.44-20.0%), Ca (7.10-33.5%), Mg (7.63-26.4%), Zn (11.6-48.7%), Mn (10.5-19.7%), Fe (12.4-22.0%), and Cu (8.86-45.3%). Ranges (in parentheses) of the RSDR values for the weighed samples were K (3.47-12.7%), Ca (7.61-34.6%), Mg (7.53-29.0%), Zn (10.6-49.2%), Mn (6.54-20.7%), Fe (11.0-21.5%), and Cu (9.73-43.0%). The Horwitz ratios (HorRat) were also used to evaluate the repeatability, HorRatr, and the reproducibility, HorRatR. Overall, the M3 method appears to be both repeatable and reproducible across the two categories for K, Mg, Zn, Mn, and Cu, and the vast majority of the HorRat values for both repeatability and reproducibility were within the acceptable range. However, a large number of soils in both the weighed and scooped categories displayed unacceptable HorRat values for the reproducibility of Ca and Fe, indicating that the M3 is not suitable for the extraction and quantitation of Ca and Fe in soils. The results of this study indicate that the M3 method for the determination of K, Mg, Zn, Mn, and Cu in soils is both accurate and precise when standardized procedures are used. The method has been proven to be suitable for use as a reference method for testing soil materials for extractable P, K, Mg, Zn, Mn, and Cu. Further study may be needed to confirm the suitability of the M3 method for Ca and Fe.

Disponibilidade de cobre e zinco em solos do sul do Brasil

O estudo da eficiência de soluções extratoras multielementares para avaliação da disponibilidade de nutrientes do solo às plantas tem aumentado. O uso dessas soluções aumenta a eficiência dos laboratórios de análise de solo devido à redução de procedimentos analíticos. Além disso, a determinação de nutrientes por espectrometria de emissão ótica por plasma induzido (ICP-OES) tem aumentado nos últimos anos, visando principalmente à redução dos procedimentos analíticos e dos limites de detecção. Com os objetivos de selecionar métodos de extração e verificar a eficiência para avaliar a disponibilidade de Cu e Zn para as plantas, foram realizados estudos em casa de vegetação e em laboratório. Em casa de vegetação, amostras de solos representativos do Estado do Rio Grande do Sul foram cultivadas, em vasos de 11 dm³ (a céu aberto), com plantas de milho (Zea mays), por 45 d e, em sequência, com soja (Glycine max), por mais 45 d. Os métodos estudados para extração de Zn e Cu foram: HCl 0,1 mol L-1 (HCl), Mehlich-1 (M1) e Mehlich-3 (M3). Os coeficientes de determinação obtidos entre as quantidade de Cu absorvida pelas plantas e o extraído pelos diferentes métodos foram: HCl = 0,56**, M1 = 0,35*; M3 = 0,46** para as plantas de milho; e HCl = 0,66**, M1 = 0,43*, M3 = 0,93** para as de soja. Para o Zn absorvido pelas plantas e o extraído pelos diferentes métodos, foram: HCl = 0,18*, M1 = 0,32**, M3 = 0,10* e HCl = 0,37*, M1 = 0,36**, M3 = 0,31*, respectivamente para as plantas de milho e de soja. Os métodos tiveram baixa capacidade preditiva na avaliação da disponibilidade de Cu e de Zn para as plantas.

Interlaboratory Validation of the Mehlich 3 Method for Extraction of Plant-Available Phosphorus

The Mehlich 3 (M3) method is widely used for extraction of plant-available phosphorus (P) from soil over a wide range of pH values. The method is also used by many laboratories to determine multiple plant-available nutrients simultaneously. However, this method has not been statistically validated within and among laboratories. The objective of this study was to determine the repeatability (within-laboratory performance) and reproducibility (among-laboratories performance) of the M3 method by using a wide variety of soils. An in-house homogeneity test was conducted for 10 soils. Three replicates of each of the 10 soils were sent to 26 domestic and international laboratories primarily for P analysis. Samples were scooped, weighed, or both scooped and weighed for extraction. The P in extracts was quantified by the participating laboratories by using inductively coupled plasma-atomic emission spectrometry (ICP-AES) or colorimetrically. For the scooped samples analyzed colorimetrically, the repeatability relative standard deviation (RSDr) ranged from 2.07 to 12.1%; the RSDr ranged from 2.2 to 21.4% for the scooped samples analyzed by ICP-AES. For the weighed samples analyzed colormetrically, the RSDr values were 1.09-9.34%, and for the weighed samples analyzed by ICP-AES, they were 1.70-5.76%. For the reproducibility data, the RSDR values ranged from 6.85 to 50.8% for the scooped-colorimetry category, from 6.95 to 73.9% for the scooped-ICP-AES category, from 7.19 to 42.6% for the weighed-colorimetry category, and from 5.29 to 35.9% for the weighed-ICP-AES category. The greatest RSD values were associated with the Susitna soil, which had the smallest concentration of extractable P. Because of the relatively small concentration of P in this soil, the laboratories were attempting to measure solution concentrations that were close to the detection limits. The Horwitz ratios (HorRat) were also used to evaluate the repeatability, HorRat(r), and reproducibility, HorRat(R). Overall, the M3 P method appears to be both repeatable and reproducible across the 4 categories, and the vast majority of the HorRat values for both repeatability and reproducibility were within the acceptable range. The results of this study indicate that the M3 P method for the determination of plant-available P in soil is both accurate and precise when standardized procedures are used. The method has been shown to be suitable for use as a reference method for testing soil materials for extractable P.

Phosphorus desorbability in soils with andic properties from the Azores, Portugal.

Desorbability of phosphorus (P des) at P sorption maxima in eighteen horizons (surface and subsurface) of soils with andic properties from the Azores, Portugal, was determined by eight successive extractions using distilled water (H2O), calcium chloride (CaCl2), Bray 2 (B2), Mehlich 3 (M3), Egner-Riehm (ER) and Olsen (OL) methods. The highest proportions of P des by the B2, M3, ER and OL methods (29-100%) were obtained in soils with weak andic properties (Vitrandic Haplustepts, Typic Haplustepts and Andic Haplustepts), indicating that P can be easily lost from these soils to nearby water bodies, through surface runoff and subsurface drainage. In contrast, low proportions of P des (4-57%) by these methods were obtained in allophanerich (Acrudoxic Hydrudands and Typic Placudands) and non-allophanic soils (Acrudoxic Hydrudands and Alic Hapludands), indicating that large amounts of P can be sorbed in an unavailable form by these soils. Of the six methods used, the proportions of P des obtained by H2O and CaCl2 were consistently lower than those obtained by the B2, M3, ER and OL methods. The proportion of P des obtained by the B2 method was highly correlated with other methods (M3, ER and OL) suggesting that the B2 is also an effective method to extract P in most of the studied soils. The proportions of P des obtained by different methods were negatively correlated with Feo and Fed, correlatios being stronger than with Alo, Ald, Alp and Fep contents. This indicates that Feo and Fed plays an important role in desorbability of P in studied soils.

Temporal and Spatial Variations of Copper, Cadmium, Lead, and Zinc in Ten Mile Creek in South Florida, USA

Lead (Pb), zinc (Zn), copper (Cu), and cadmium (Cd) often seriously deteriorate water quality. Spatial and temporal fluctuations of the metal concentrations in the Ten Mile Creek (Florida) (TMC) were monitored on a weekly basis at 7 sampling sites, from June 2005 to September 2007. River sediment samples were also collected from these sites in April, June, and October 2006 and January 2007, and analyzed for water, Mehlich 1 (M1), and Mehlich 3 (M3)-extractable metals (Mehlich, 1953, 1984), to examine the role of sediments as sources or sinks of the metals. The concentrations of lead, zinc, copper, and cadmium in the water samples were <detection limit (DL)-309, < DL-102, < DL-106, and < DL-15.7 microg/L, respectively. Even though median concentrations of lead (<DL), zinc (6.45 microg/L), copper (2.53 microg/L), and cadmium (<DL) were lower than their respective U.S. Environmental Protection Agency (Washington, D.C.) limits for freshwater (2.5 microg/L for lead, 120 microg/L for zinc, 9.0 microg/L for copper, and 0.25 microg/L for cadmium), pulse concentrations of the metals significantly exceeded these limits. Correlations of lead, zinc, copper, and cadmium concentrations in the TMC to other environmental factors, including the results of principal component analysis, suggest that there are different sources of metals. These sources include surface runoff from agricultural lands or urban wastewater, geological backgrounds, and tidal flow. Water-, M1-, and M3-extractable lead, zinc, copper, and cadmium concentrations in river sediments indicate the possibility that river sediment serves as an internal source of the metals for the TMC. This hypothesis was supported by positive correlations between concentrations of copper, lead, and zinc in the river water and their respective water-extractable concentrations in the sediments.

Interpretação de resultados analíticos de fósforo pelos extratores Mehlich-1 e Mehlich-3 em solos do Rio Grande do Sul

As soluções extratoras multielementares possibilitam avaliar a disponibilidade de vários nutrientes de plantas no mesmo extrato; dentre estes o P merece especial atenção. As soluções Mehlich-1 (M1) e Mehlich-3 (M3) enquadram-se nesta categoria. Neste estudo, foram comparados os teores de P extraídos por estas soluções em 360 amostras de solos do Estado do Rio Grande do Sul. Os coeficientes de correlação entre os teores de P extraído pelas mesmas indicaram alto grau de associação e de significância. Os teores de P extraído pela solução Mehlich-3 foram, em média, 50 % maiores que os extraídos pela solução Mehlich-1. O teor de argila, entretanto, influenciou a capacidade extrativa de P pela solução Mehlich-3, sendo necessária uma tabela de ajuste para a interpretação dos valores do P extraído por esta solução.

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

: 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.

Cadmium, Lead, Copper, Zinc, and Nickel in Lettuce and Dry Beans as Related to Mehlich-3 Extraction in Three Brazilian Latossols

ABSTRACT Lettuce (Lactuca sativa L.) and dry beans (Phaseolus vulgaris L.) were grown in three Brazilian Red-Yellow Latossols (Oxisols) in greenhouse conditions with cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), and nickel (Ni) applied to soils in treatments arranged as a randomized complete block design. Plant metals were analyzed in lettuce shoots and dry beans roots, stems, leaves, and seeds. After plant growth, soil samples from the pots were extracted with Mehlich-3 (M-3) for metal availability evaluation. The release of Ni in the M-3 extraction was dependent on the soil exchangeable aluminum (Al3 +). Mehlich-3 was efficient for determination of availability of Cd, Pb, Cu, Zn, and Ni for dry beans and availability of Cd and Ni for lettuce. The dry bean leaves Cd, Pb, Cu, Zn, and Ni were highly correlated with their recovering from soils with M-3. The same was observed for Cd and Ni in lettuce shoots and the M-3 recovered metals from soils.

Phosphorus sorption maxima and desorbability in selected soils with andic properties from the Azores, Portugal

P sorption and desorption capacities were determined on 30 soil horizons (surface and subsurface) of soils with andic properties from the Azores, Portugal, using the Langmuir equation and successive extractions with dilute calcium chloride (CaCl 2), respectively. The proportion of P recovery (P rec) using distilled water (H 2O), CaCl 2, Bray 2 (B2), Mehlich 3 (M3), Egnér–Riehm (ER) and Olsen (OL) extractants was also determined to assess the extent of P release from soils enriched with P at P sorption maxima (P m). Soils containing very low amounts of organic C and allophane (Vitrandic Haplustepts and Vitrandic Udorthents) showed the lowest values of P m (48–565 mg kg − 1 ) and the highest values of P desorbability (P des) (69–100%), indicating that P can be easily lost from these soils. Application of fertilizers to these soils should be restrained in order to minimize eutrophication risk of nearby water bodies. In contrast, allophanic and non-allophanic horizons of Typic Placudands, Alic Hapludands, Acrudoxic Hapludands and Acrudoxic Hydrudands showed much higher values of P m (2273–52,400 mg kg − 1 ) and lower values of P des (4–57%).They also showed low proportions of P rec by the used extractants, indicating that large amounts of P can be sorbed in an unavailable form. Thus, these soils may require large amounts of P fertilizers and an efficient method of P application. Other studied soils with high amounts of 1:1 layer silicate minerals and having weak andic properties (Typic and Andic Haplustepts), showed intermediate P m (1124–8333 mg kg − 1 ) and P des values (20–63%). The values of P m were positively correlated with Al d, Al o, allophane, Fe o, Fe d and Al p contents, and with the values of Al o + 1/2 Fe o. In contrast, values of P des were negatively correlated with these soil constituents. Of the six extractants, the B2 extractant showed generally higher proportions of P rec than the other extractants in most studied soils. The proportions of P rec by the B2, M3, ER and OL extractants were negatively correlated with contents of Fe o, Fe d, Al d, Al o, Al p, and Fe p, and with the values of Al o + 1/2 Fe o and PR.

Variations in Stream Water and Sediment Phosphorus among Select Ozark Catchments

Stream sediments play a large role in the transport and fate of soluble reactive phosphorus (SRP) in stream ecosystems, and equilibrium P concentrations (EPC 0) of benthic sediments at which P is neither adsorbed nor desorbed are often related to stream water SRP concentrations. This study evaluated (i) the variation among water chemistry and sediment-P interactions among streams draining catchments that varied in the land use; (ii) the relations between SRP concentration, sediment EPC 0, and other measured abiotic factors (e.g., particle size distribution, slope of linear sorption isotherms, etc.) in the stream sediments; and (iii) the use of the traditional Mehlich-3 (M3) soil extraction on stream sediments to elucidate other abiotic factors (e.g, M3P, P saturation ratio, etc.) related to SRP concentration in stream sediments. Stream water and sediments were sampled at 22 selected Ozark streams in northwest Arkansas during fall 2003 and spring 2004. Nitrate-N concentrations in the water column (r = 0.69) and modified P saturation ratios (PSR mod) ) of the benthic sediments (r = 0.79) at the selected streams increased with an increase in percent pasture in the catchments, whereas SRP concentration (r = -0.56) and Mehlich-3-extractable P (M3P) content (r = -0.47) decreased with an increase in the percent forested area. Soluble reactive P concentrations in the stream water were positively correlated to sediment EPC 0 (r = 0.51), although sediment EPC(0) was generally greater than SRP. The M3 soil extraction was useful in identifying abiotic factors related to SRP concentrations in the selected streams, in particular SRP concentrations were positively correlated to M3P contents (r = 0.50) and PSR mod (r = 0.71) of the benthic sediments. Thus, M3P and EPC 0 estimates from stream sediments may be valuable yet simple indicators of whether benthic sediments act as sinks or sources of P in fluvial systems, as well as estimating changes in stream SRP concentrations.

Elemental Status in Sediment and American Oyster Collected from Savannah Marsh/Estuarine Ecosystem: A Preliminary Assessment

Sediment and American oyster (Crassostrea virginica) collected from nine selected marsh/estuarine ecosystems in Savannah, Georgia were analyzed for elements such as Al, As, B, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Si, and Zn. Sediments were extracted by ammonium acetate (NH(4)OAc), Mehlich-3 (M-3), and water procedures, whereas an acid digestion procedure was adopted for oyster tissue. Concentrations of elements were higher in M-3 extractions followed by NH(4)OAc and water extraction procedures. Calcium and Mg was greater in sediments by any of the extractions, whereas other elements differed depending upon the extraction procedures. There were no significant spatial variations (p < 0.05) of any of elements analyzed except Mn, in NH(4)OAc/water extraction procedure and Fe and Al by water extraction procedure. Contamination of Al, B, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Si, and Zn in oyster tissue ranged from 399 to 1460, 231 to 254, <1.5 to 2.9, <1.5 to 8.0, 67 to 121, 232 to 1357, 17 to 54, <0.5 to 0.64, <1.5 to 2.5, <1.5 to 4.0, 241 to 381, and 978 to 2428 microg/g dry weight (dw), respectively. Greatly elevated concentrations of elements such as P, Ca, Mg, K, and S were noticed in oyster tissue. The concentration range of Hg and As in sediment was 1.2-1.9 and 11-55 microg/g dw, respectively. The concentration range of Hg and As in oyster tissue was 130-908 and 200-912 ng/g dw, respectively. With the exception of As and Hg, other elements are several orders of magnitude greater in oyster tissue. There is no significant (p < 0.05) contamination variation in target analyses between the nine selected sites. Concentrations of heavy metals in sediment and oyster were either comparable or lower than those of other countries. Greater biota-sediment accumulation factor was noticed for P and Zn. Concentrations of Hg and P in oyster tissue were higher than the threshold limit for human consumption. Overall, the baseline data can be used for regular ecological monitoring, considering the domestic and industrial growth around this important marsh/estuarine ecosystem.

Soil and Tissue Phosphorus, Potassium, Calcium, and Sulfur as Affected by Dairy Manure Application in a No‐Till Corn, Wheat, and Soybean Rotation

The hypothesis of this study was that surface applied liquid manure may provide sufficient nutrients to silage corn (Zea mays L.), wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.] under a no‐till system in the cool wet climate of Atlantic Canada. A 2‐yr field study was conducted investigating the effect of crop rotation and fertility on P, K, Ca, and S availability to corn silage, spring milling wheat, and soybean in Nova Scotia, Canada. The rotations consisted of all six possible combinations of corn, wheat, and soybean, and the fertility treatments consisted of three rates of liquid dairy manure (LDM1–3) at 32.1, 48.1, and 64.3 Mg ha−1, a mineral fertilizer treatment, and a control (no fertility applied). In general, nutrient availability as measured by Mehlich 3 (M3) was not well correlated with tissue concentration. Tissue S in corn was lower when it was grown after soybean than when grown after wheat, and was highest in the LDM1 and in the control treatments. Rotation × fertility effects observed in the wheat nutrient removals were accountable to similar differences in yield. Wheat uptake of P was significantly affected by fertility, with the highest removal of P occurring in the NPK treatment, which also provided the highest yield. Results indicate that Ca uptake by wheat may be hindered by competition with K, and that K applied in manure at higher rates could build up over time. Potassium recovery in wheat was higher from the inorganic NPK treatment (37%) than from manure (from 16 to 4%). There were few differences in M3 available nutrients in 2001. However in 2002, LDM application resulted in higher M3 concentrations of K and Ca; there was a drop in P availability with the LDM3 (at 64.3 Mg ha−1) application; and S availability was highest at LDM1 and LDM3 (32.1 and 64.3 Mg ha−1, respectively). Further long‐term studies may be needed to determine if surface applied LDM with no incorporation can sustain silage corn, soybean, and wheat nutrient requirements for P, Ca, K, and S, and maintain efficient nutrient use overtime under no‐till conditions.

Factors Affecting Change in Soil Test Phosphorus Following Manure and Fertilizer Application

In many states, Morgan (M) or Mehlich‐3 (M3) extractions are the basis for P fertility recommendations and P runoff risk assessment. The impact of timing of sampling, P source, and extractable Al on agronomic soil test P (STP) and P release to the environment are not well understood. Incubation studies were conducted to determine: (i) changes in M‐P, M3‐P, and 0.01 M CaCl2–P with time following Ca(H2PO4)2 addition; (ii) the efficiency of liquid dairy manure, NH4HPO4, and Ca(H2PO4)2 in raising M‐P and M3‐P levels; and (iii) the degree to which initial P and extractable Al impact the efficiency of applied P. Twenty‐eight noncalcareous soils were incubated at 23°C, in the dark, at field capacity moisture content. Extractable P decreased over 60 d, with a greater proportion of P being lost from the more labile pools (CaCl2–P &gt; M‐P &gt; M3‐P). The increase in STP per unit P added (ΔP‐M and ΔP‐M3) was affected by P source: NH4HPO4 raised P levels more efficiently than Ca(H2PO4)2 or liquid dairy manure. There was a positive linear relationship between ΔP and initial STP. Extractable Al was inversely related to ΔP‐M and ΔP‐M3 and followed exponential decay functions. Extractable Al was positively and linearly related to the amount of P required to raise M‐P and M3‐P levels 1 mg kg−1, with Morgan Al as the most accurate predictor of ΔP. Our results suggest that the New York P index should include guidance on sampling time and account for the higher P sorption capacity of soils inherently high in extractable Al.

Soil Test to Predict the Copper Availability in Pasture Soils

The proportion of copper (Cu) that can be extracted by soil test extractants varied with the soil matrix. The plant‐available forms of Cu and the efficiency of various soil test extractants [(0.01 M Ca(NO3)2, 0.1 M NaNO3, 0.01 M CaCl2, 1.0 M NH4NO3, 0.1 M HCl, 0.02 M SrCl2, Mehlich‐1 (M1), Mehlich‐3 (M3), and TEA‐DTPA.)] to predict the availability of Cu for two contrasting pasture soils were treated with two sources of Cu fertilizers (CuSO4 and CuO). The efficiency of various chemical reagents in extracting the Cu from the soil followed this order: TEA‐DTPA>Mehlich‐3>Mehlich‐1>0.02 M SrCl2>0.1 M HCl>1.0 M NH4NO3>0.01 M CaCl2>0.1 M NaNO3>0.01 M Ca(NO3)2. The ratios of exchangeable: organic: oxide bound: residual forms of Cu in M1, M3, and TEA‐DTPA for the Manawatu soil are 1:20:25:4, 1:14:8:2, and 1:56:35:8, respectively, and for the Ngamoka soil are 1:14:6:4, 1:9:5:2, and 1:55:26:17, respectively. The ratios of different forms of Cu suggest that the Cu is residing mainly in the organic form, and it decreases in the order: organic>oxide>residual>exchangeable. There was a highly significant relationship between the concentrations of Cu extracted by the three soil test extractants. The determination of the coefficients obtained from the regression relationship between the amounts of Cu extracted by M1, M3, and TEA‐DTPA reagents suggests that the behavior of extractants was similar. But M3 demonstrated a greater increase of Cu from the exchangeable form and organic complexes due to the dual activity of EDTA and acids for the different fractions and is best suited for predicting the available Cu in pasture soils.

Differences of Phosphorus in Mehlich 3 Extracts Determined by Colorimetric and Spectroscopic Methods

Mehlich 3 (M3) is a widely used extractant for evaluating plant available phosphorus (P) in soils and may be quantified using colorimetric or inductively coupled plasma (ICP) spectroscopic methods. Analysis by ICP has recently become increasingly popular in soil‐testing labs primarily due to its ability to simultaneously measure multiple elements. Despite the versatility and efficiency of ICP, some laboratories hesitate to use ICP to determine P in M3 extracts because (1) fertilizer recommendations were developed using colorimetric analysis, and (2) differences have been reported between P analyzed colorimetrically and by ICP. This study documented the differences between M3 P measured colorimetrically using a flow injection auto‐analyzer and by ICP (ICP‐P) for approximately 6400 routine soil samples analyzed by the Soil, Water and Forage Analytical Laboratory at Oklahoma State University. Potential factors contributing to the difference in colorimetric P and ICP‐P were also examined using another set of 100 well‐characterized soils. Mean ICP‐P was greater than colorimetric P (p<0.001) for both sets of soils. Highly significant relationships existed between colorimetric P and ICP‐P for the 6400 soils (r2=0.98, p<0.001) and for the 100 soils (r2=0.97, p<0.001). The relative difference between colorimetric P and ICP‐P decreased exponentially with increasing (soil test P measured) colorimetrically. Significant relationships did not exist (p>0.05) between the relative difference in colorimetric and ICP‐P and soil properties, including soil pH, clay content, organic carbon content, or M3 extractable aluminum (Al), calcium (Ca), and iron (Fe). Fertilizer recommendations based on colorimetric P predicted by ICP values were highly related (r2=0.81, p<0.001) to fertilizer recommendations based on actual colorimetric P.

Path and Multiple Regression Analyses of Phosphorus Sorption Capacity

Soil P saturation indices and P Langmuir adsorption maximum (Smax) are two environmental soil tests that provide valuable information for the proper management P in soils to avoid the overapplication of P. The objectives of this study were to determine Smax and develop P saturation indices for 28 Oklahoma benchmark soils and to use path analysis and multiple regression to examine the relationships between Smax and soil properties. Soil samples were analyzed for pH, clay content, oxalate extractable P (Pox), Al (Alox), Fe (Feox), and Mehlich-3 (M3) extractable P (PM3), Al (AlM3), Fe (FeM3), Ca (CaM3), and Mg (MgM3). The Smax value and saturation indices based on oxalate and M3 extractions were determined. The Smax value ranged from 34 to 500 mg kg−1 and was highly correlated with clay content (r = 0.79), organic C (r = 0.80), Alox (r = 0.88), and Feox (r = 0.83). Soil pH was not correlated (p> 0.05) with Smax Path analysis showed significant direct effects (p< 0.01) between Alox and Smax and between Feox and Smax but these relationships were highly influenced by indirect effects of Alox and Feox Multiple regression agreed well with path analysis and found that the combination of Alox and Feox were the two most important soil properties related to Smax of the soils studied. Significant relationships existed between AlM3 (r = 0.54) and Smax and between FeM3 (r = 0.54) and Smax Three P saturation indices studied were highly correlated (p< 0.05) with each other. Our results show that Smax of Oklahoma soils may be predicted with oxalate extractable Al and Fe or M3 extractable Al, Fe, and Ca.

Comparison of different phosphorus extraction and determination methods using manured soils

Soil test P (STP) methods were developed for fertilizer P recommendation in crop production. As soil P content of arable land increases due to manure application, the suitability of these STP methods for assessing P runoff potential from a field needs to be evaluated. The objective of this research was to evaluate various P extraction and determination methods using manured soils for their potential use as environmental P testing methods. Eighty one soil samples were taken in 1998 from various manured fields and research plots across Alberta. Phosphorus in the samples was extracted using deionized water, Miller-Axley (0.03 M NH4F + 0.015 M H2SO4), modified Kelowna (0.015 M NH4F + 0.25 M NH4OAc), and Mehlich 3 (M3) (1.5 M NH4F + 0.1 M EDTA) procedures. Phosphorus concentration in all extraction solutions was determined by the molybdenum blue colorimetric method in a Technicon II autoanalyzer. In addition, P content of the deionized water and M3 extractions was determined by an inductively coupled plasma emission spectroscopy (ICP) method. Soluble organic carbon content was measured in the deionized water extraction. The extractable P concentration increased as the acidity of the extraction solution increased in the order: M3 &gt; modified Kelowna &gt; Miller-Alxey &gt; deionized water. The P extracted by Miller-Axley and M3 was strongly related to the deionized water extractable P, suggesting that both methods may be useful in assessing potential P runoff from arable land. The P concentration by the ICP determination was much higher than with the colorimetric method in M3 and the deionized water. The P concentration difference between the two determination methods was largely correlated to the soluble organic carbon in the deionized water extraction (r = 0.828***), suggesting that the undetected P by the molybdenum blue colorimetric method may exist in organic forms. To asses P runoff risk from arable land, both soluble inorganic and organic P need to be considered, and the ICP method can determine the total P, which includes both. In developing a STP for environmental soil P management, both P extraction and P determination methods should be standardized, and our results suggest that M3 and Miller-Axley extraction, and ICP determination are suitable methods for assessing P runoff. Key words: Soil test P, colorimetric P, ICP-P, dissolved organic carbon, soluble organic P, manure application rate

Metal extraction by Alyssum serpyllifolium ssp. lusitanicum on mine-spoil soils from Spain

The efficiency of Alyssum serpyllifolium ssp. lusitanicum (Brassicaceae) for use in phytoextraction of polymetallic contaminated soils was evaluated. A. serpyllifolium was grown on two mine-spoil soils (MS1 and MS2): MS1 is contaminated with Cr (283 mg kg −1) and MS2 is moderately contaminated with Cr (263 mg kg −1), Cu (264 mg kg −1), Pb (1433 mg kg −1) and Zn (377 mg kg −1). Soils were limed to about pH 6.0 (MS1/Ca and MS2/Ca) or limed and amended with NPK fertilisers (MS1/NPK and MS2/NPK). Biomass was reduced on MS2/Ca due to Cu phytotoxicity. Fertilisation increased biomass by 10-fold on MS1/NPK, but root growth was reduced by 7-fold compared with MS1/Ca. Plants accumulated Mn, Ni and Zn in shoots, and both metal content and transportation were generally greater in MS2 than in MS1. Zinc bioaccumulation factors (BF, shoot [metal]/soil [metal]) were significantly greater in MS2 than in MS1. However, metal yields were greatest in plants grown on MS1/NPK. Concentrations of EDTA-, NH 4Cl- and Mehlich 3 (M3)-extractable Mn and Zn were greater after plant growth. Concentrations of M3-extractable Cr, Ni, Pb and Zn were increased at the rhizosphere. Sequential extractions showed changes in the metal distribution among different soil fractions after growth. This could reflect the buffering capacity of these soils or the plants' ability to mobilise metals from less plant-available soil pools. Results suggest that A. serpyllifolium could be suitable for phytoextraction uses in polymetallic-contaminated soils, provided Cu concentrations were not phytotoxic. However, further optimisation of growth and metal extraction are required.