Ammonium Chloride Solution as an Alternative Laboratory Procedure for Exchangeable Cations in Southern Brazilian Soils

Most Brazilian soil-testing laboratories use Mehlich 1 and 1.0 M potassium chloride (KCl) solutions as extractants for the determination of phosphorus (P), potassium (K), and sodium (Na) and for exchangeable calcium (Ca), magnesium (Mg), manganese (Mn), and aluminum (Al) in agricultural soil samples. Other laboratories use a combination of exchangeable ionic resin and KCl procedures. With recent adoption of the inductively coupled plasma (ICP-OES) in routine soil-testing laboratories, soil extraction with 1.0 M ammonium chloride (NH₄Cl) became an alternative due to the possibility of determining all exchangeable elements in one run (Ca, Mg, K, Mn, Na, and Al), leaving determination of phosphorus (P) with Mehlich 1 or exchangeable ionic resin. To evaluate the performance of the NH₄Cl solution, an experiment was carried out with thirty-seven samples of soils representative of the southernmost state of Brazil, Rio Grande do Sul. Four extraction solutions [Mehlich 1 at soil/solution ratio of 1:10 and 1.0 M ammonium acetate (NH₄OAc), 1.0 M KCl, and 1.0 M NH₄Cl at soil/solution ratio 1:20] were used with three different shaking times (5, 30, and 60 min). Correlation coefficients among all methods were high. Mehlich 1 did not perform well against NH₄OAc and NH₄Cl, despite the high correlation coefficients, with values consistently lower for K, even when the time of extraction was increased from 5 to 30 or 60 min. However, for concentrations less than 0.30 cmol kg^?1 (i.e., in the range of K deficiency), both solutions performed similarly. Calcium and Mg increased with time of shaking. Comparable values of exchangeable Ca, Mg, and K, as well as of Al and Mn, were obtained with 1.0 M NH₄Cl with 60 min shaking and the standard procedures of 1.0 M NH₄OAc and 1.0 M KCl. The determination of Al by traditional titration/back-titration of the 1.0 M KCl solution gave slightly greater results compared to ICP-OES obtained using extraction with 1.0 M NH₄Cl. The results indicate that for Ca, Mg, Mn, and Al, it is possible to replace the traditional 1.0 M KCl extraction with 1.0 M NH₄Cl solution, with 60 min shaking time and a soil/solution ratio of 1:20.     

Citric acid extraction—An underestimated method in forest nutrition?

Since recent studies reveal citric acid to be favorable for estimating plant‐available P in soils, we investigated if it can also be used for assessing other nutrients. According to our results, it provides stronger correlations with the tree nutrition for Mg (beech, spruce), Ca+K (beech) and Fe (spruce) than the standard methods for determining exchangeable cations. Thus, when estimating plant‐available P by citric acid‐extraction, these cations should be additionally measured in ICP analysis.     

Comparison of extractants for the determination of available phosphorus,potassium, calcium,magnesium and sodium in some Ethiopian and German soils

Abstract

A study was conducted with the purpose of comparing the efficiency of Mehlich 1, Mehlich 3, and calcium acetate lactate (CAL) extractants for the deter‐ mination of available phosphorus (P) and exchangeable cations [potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)] on 22 Ethiopian and 10 German agricultural soils. The Olsen and NH₄OAc extractants were used as standards against which P and exchangeable cations values were compared. Results showed that, in general, highly significant correlations were found between all of the methods for available P and exchangeable cations determination on the Ethiopian soils. The highest correlation was, however, found with the Mehlich 3 extractant. On the ten soils from Germany, the Olsen method did not give significant cor‐ relation with the CAL method for P determination. The CAL and Mehlich 3 extrac‐ tants were also not good indicators of Na availability when compared with the NH₄OAc method. It can be generalized that the Mehlich 3 is a suitable extractant for P, K, Ca, Mg, and Na in Ethiopian soils, but further study is recommended to confirm these findings under field conditions.     

Plant Availability of Cadmium in Soils: II. Factors Related to the Extractability and Plant Uptake of Cadmium in Cultivated Soils

Abstract

Eighty four soil samples collected from southeastern Norway were analyzed for Cd by extraction with NH₄OAc, DTPA, NH₄OAc-EDTA, NH₄NO₃, HCl and CaCl₂. The total Cd, pH, exchangeable K and Ca, dithionite-extractable Mn, available P and fine sand (0.2–0.02 mm) contents were the principal factors related to the extractable Cd, with some inter-extractant variations. Cadmium extracted by NH₄NO₃, NH₄OAc, HCl and CaCl₂ decreased with increasing soil pH, but the Cd extracted by all the extractants increased with increasing total Cd, exchangeable K and Ca, available P, and Mn-oxide contents in the soils. The Cd concentrations in plants were significantly related to the extractable Cd, exchangeable Ca and Mg, pH, Mn-oxides and organic matter content.     

High soil Mn and Al,as well as low leaf P concentration,may explain for low natural rubber productivity on a tropical acid soil in Vietnam

The aim of the current study was to identify major soil and leaf factors accounting for low natural rubber (NR, Hevea brasiliensis) productivity on tropical acid Acrisols in Vietnam. Twenty NR plots were measured with NR productivity, leaf factors (N, P, K, Ca, Mg, Mn, Cu, Fe, and Zn), soil factors (pH, particle size distribution, total C, N, P, K, exchangeable K, Ca, Mg, Al, Mn, Fe, Zn, available P). Cluster analysis showed that NR productivity could be separated into three clusters with low (23.2), medium (38.2), and high (61.3 g tree^?1 harvest^?1) yield. High-yield cluster had higher leaf P concentration and soil pH, while low-yield cluster had higher leaf Mn, soil exchangeable Al, and Mn concentration. Simple and multiple linear regression analysis applied with backward elimination procedure suggested that leaf and soil toxic concentration may be responsible for low NR productivity in the study soil.     

A comparison of methods for measuring extractable Ca,Mg, K,Na, Mn,Al, Fe,and P from New England forest soils

Abstract

An experiment was designed to evaluate several of the commonly used extractants and methods for determining “available”; elements in soils. The purpose of the study was to evaluate the suitability of these extraction procedures for use on forest soils typical for New England commercial forests. The extraction procedures selected included NH₄OAc pH 4.8, NH₄OAc pH 7.0, NH₄Cl, Double Acid, Bray, and Mehlich methods. The elements measured varied somewhat by procedure but included the base cations, Al, Fe, Mn, and P. As a bioassay of element availability, a greenhouse study was conducted using six forest soil materials from different horizon types (i.e. O, Ap, B) and three conifer seedling species (red spruce, balsam fir, and white pine). Relatively small differences among extraction procedures were found among the methods used for exchangeable Ca, Mg, K, and Na. Large differences, however, were found among the different horizon types in the amount of exchangeable base cations present. In contrast, significant differences were found among extraction procedures for Al, Fe, Mn, and P depending on the degree of buffering and acidity of the extracting solution. Of the elements measured in this study, only P appeared to be growth limiting with the NH₄OAc pH 4.8 being best correlated with P uptake by seedlings. Further work under field conditions over longer time periods is required to evaluate these methods for measuring P availability in forest soils     

Nitrogen and/or phosphorus fertilization effects on organic carbon and mineral contents in the rhizosphere of field grown sorghum

The effects of nitrogen (N) and/or phosphorus (P) fertilizers on the nutritional status in the rhizosphere were studied by monitoring throughout the growth period the concentrations of organic carbon (C), inorganic N, NaHCO₃ extractable P, exchangeable K, Ca, and Mg in sorghum (Sorghum bicolor L. Moench) down in an Alfisol field, and of all these elements except for extractable P, and exchangeable Ca in a Vertisol field in semi-arid tropical India. These concentrations were compared between the rhizosphere soil and bulk soil of sorghum grown in both fields.

Organic C content of the rhizosphere soil increased with plant age and was significantly higher than that in the bulk soil throughout the growth of sorghum, but it was not affected by the rates of N or P fertilizer. Inorganic N concentration in the rhizosphere soil was significantly higher than that in the bulk soil until maturity in sorghum. The content of available P in the rhizosphere soil was significantly higher than in the bulk soil after the middle of the growth stage. Its average concentration in the rhizosphere soil across growth stages was significantly higher than in the bulk soil, which contradicts the observation in many reports that there is a depletion of P in the rhizosphere soil. The concentration of three exchangeable cations, K, Ca, and Mg, showed different patterns in the rhizosphere and the bulk soils. The concentration of K was almost constantly higher in the rhizosphere soil than in the bulk soil, Ca concentration was not different between the two soils, and Mg concentration was significantly higher in the bulk soil than in the rhizosphere soil. The reasons for these discrepancies cannot be explained at present. The concentrations of these cations were not affected by the rate of N or P fertilizer except for Mg at a later growth stage. The differences between rhizosphere and bulk soils in Alfisol were similar to those in Yertisol with respect to the concentration of organic C, inorganic N, and exchangeable K and Mg.     

Mehlich3方法与常规方法测定土壤养分相关性初步研究

采取Mehlich3(以下简称M3法)方法和常规标准方法测定了41个土壤样品的有效磷、速效钾、交换性钙、交换性镁、有效铁、有效锰、有效铜、有效锌和有效硼。通过对两种方法测定结果的分析,探讨二者的相关性。土壤有效磷M3方法与常规方法相关系数达到0.9085,为最高,有效铜M3方法与常规方法相关系数为0.1556,为最低。有效铜、有效硼测定结果的相关性很差。M3方法与常规方法测定土壤养分在有效磷、速效钾、交换性钙、交换性镁、有效铁、有效锰、有效锌上达到极显著水平,其数值可以通过回归方程相互转换利用。     

黄土高原刺槐林对土壤养分时空分布的影响

以不同树龄刺槐纯林林地和撂荒地作对比,研究了黄土高原刺槐人工林对土壤养分时空分布特征的影响。结果表明,刺槐林地土壤有机质、pH值、全氮、有效氮、有效磷、速效钾、交换性钙和交换性盐基总量随刺槐树龄增加无明确变化规律,土壤全磷和交换性镁含量则呈现波动性变化;刺槐林地土壤有机质、全氮、有效氮含量随土壤深度增加按幂函数衰减,有效磷含量有递减趋势,土壤全磷、速效钾、交换性钙、交换性镁和交换性盐基总量随土壤深度增加无明显变化规律,而土壤pH随深度呈波动性变化;与撂荒地相比,刺槐林地土壤有机质、全氮、有效氮、有效磷、速效钾、交换性钙、交换性镁含量及交换性盐基总量分别增加21.6%~96.8%,34.3%~160.1%,191.5%~238.4%,2.1%~24.1%,19.82%~92.71%,64.2%~80.0%,25.0%~46.5%和67.2%~89.5%,表明刺槐林对改善土壤养分状况具有重要作用。     

影响山核桃林地土壤生产性能的主要肥力因子及其临界区间

【目的】土壤养分是植物生存的必要条件,探讨山核桃(Carya cathayensis Sarg.)主产区林地土壤肥力因子及其对土壤生产性能的影响,为山核桃的栽植和可持续发展、土壤培肥提供科学依据。【方法】在浙江省山核桃主产区,随机选择58个典型乡镇的山核桃林采集土样,测定了pH、有机质、碱解氮、有效磷、速效钾、有效钙、有效镁、有效铁、有效锰、有效铜、有效锌、有效硼12个肥力因子水平,运用主成分分析和回归分析方法,分析了它们对山核桃生长、感病等级、产量等级的影响以及丰缺临界区间。【结果】主成分分析前5个因素(PC1、PC2、PC3、PC4、PC5)的累计贡献率达78.49%。PC1的主要荷载为土壤pH、有效钙和有效镁含量,PC2的主要荷载是微量元素和有效磷含量,PC3是有机质和碱解氮含量,PC4和PC5分别是有效硼和速效钾含量。林分生长性状中,生长势等级与pH、速效钾、有效钙、有效镁、有效铜、有效锌显著负相关(P <0.01),干腐病感病等级与pH、有效钙、有效镁显著负相关(P <0.01),产量等级与pH、有效钙、有效镁、有效磷、有效锌显著正相关(P <0.01)。回归模型分析得出,土壤pH、速效钾和有效钙、有效镁、有效铜、有效锌是当前栽培措施水平下影响山核桃生长的关键土壤肥力因子。综合评价后发现,研究区现有约57%的山核桃林地土壤综合肥力低于平均水平。【结论】对山核桃林地土壤生产性能影响最大的因素是土壤pH、有效钙和有效镁含量,其次是微量元素和有效磷含量,有机质、速效钾含量也有一定的影响。山核桃主产区的林地土壤关键指标丰缺范围:pH 5.19~5.70、速效钾87~129 mg/kg、有效钙817~1374 mg/kg、有效镁93~145 mg/kg、有效铜1.36~4.39 mg/kg、有效锌0.78~2.33 mg/kg。     

A rapid method to determine cation exchange capacity and exchangeable bases in calcareous,gypsiferous, saline and sodic soils

Summary

A simple, single‐step extraction with LiEDTA for the estimation of CEC and exchangeable bases in soils has been developed. Multivalent cations are stripped from the soil adsorption sites by the strongly chelating agent EDTA, and are replaced by Li. In soils without CaCO₃ or water soluble salts, exchangeable divalent cations (Ca, Mg) are chelated by EDTA and exchangeable monovalent cations (Na, K) are replaced in a single extraction step using 0.25–2.5 g of soil and 10.0 ml of extractant.

In calcareous soils the CEC can be determined in the same way, but for the extraction of exchangeable Ca and Mg, another separate extraction is needed because dissolution of calcite by EDTA is unavoidable. This extraction is done with as much NaEDTA as needed to extract only exchangeable Ca and Mg in a 1:2 (m/V) soil/alkaline‐50% (V/V) aethanolic solution to minimize dissolution of calcite.

In gypsiferous soils gypsum is transformed into insoluble BaSO₄ and soluble CaEDTA by LiBaEDTA thus avoiding interference of Ca from dissolution of gypsum, which renders the traditional methods for determining CEC unsuitable for such soils. To determine exchangeable Ca and Mg, Na₄EDTA is used as for calcareous soils.

In saline/sodic soils replacement of Na by Li is incomplete but the Na/Li‐ratio at the complex after extraction is proportional to the molar Na/Li‐ratio in the extracts, so that the CEC and original exchangeable sodium (ESP) content can be calculated. Additional analysis of Cl and, if necessary, SO₄ in the extracts of saline soils can be used to correct for the effect of dissolution of the salts on the sum of exchangeable cations.

This new method is as convenient as the recently developed AgTU (silverthiourea), but is better suitable for calcareous and gypsiferous soils.     

EFFECT OF SOIL pH AND ORGANIC MATTER ON LABILE ALUMINIUM IN SOILS UNDER PERMANENT GRASS

The rates of extraction of Na, K, Mg, Ca, and Al with 1M NH₄ NO₃ from the mineral-and organic-rich layers of some Park Grass (Rothamsted) soils were measured at the pH of the soil. Below pH 3.7 exchangeable Al, derived from the kinetics curve, increases with decreasing soil pH and is less in the organic-rich layer. The sum of the basic exchangeable cations, ∑(Na + K + Mg + Ca), increases with increasing soil pH and is more in the organic-rich layer. The extraction of exchangeable Al obeys first order kinetics, the rate constant being similar for all the soils (mean value 36 ± 7 × 10^?6|s^?1), which implies that exchangeable Al is released from surfaces with similar properties for the adsorption of Al, and that the rate is not affected by soil pH and organic matter. The rate of extraction of non-exchangeable Al is the same in the mineral-and organic-rich layers of each soil, and is maximal at about pH 3.7, decreasing sharply at more and less acid pH values.     

鼎湖山季风常绿阔叶林土壤酸度对土壤养分的影响

通过在鼎湖山季风常绿阔叶林的研究发现 :( 1 )季风常绿阔叶林土壤整个剖面 ( 0～ 60cm)pH值都较低 ,小于 4 5。 ( 2 )土壤养分含量随着土壤剖面层次 ( 0～ 2 0cm、2 0～ 40cm、40～ 60cm)的降低而下降。养分除水解性N外 ,有效P、速效K以及交换性Ca、Mg含量都很少。 ( 3 ) 0～ 2 0cm土壤养分比其它层的土壤养分更容易受到土壤酸度的影响。 40～ 60cm土壤养分除了交换性Ca外 ,其它养分的含量与土壤酸度无显著关系。就不同月份来说 ,1月份和 4月份土壤养分比 7月份和 1 0月份土壤养分容易受到土壤pH值的影响。不同养分比较 ,交换性Ca和Mg以及有效P含量比其它养分更容易受到土壤酸度的影响。     

A simple rapid method for the measurement of exchangeable cations and effective cation exchange capacity

Abstract

A simple single‐extraction procedure for measuring exchangeable cations and effective CEC (ECEC, the CEC at natural pH and ionic strength) has been developed for routine advisory soil analysis. The method is based on the use of Sr (1.26M SrCl₂) to displace exchangeable cations and effective CEC is taken as the sum of the exchangeable cations. A ten minute shaking time at 5 g:80 ml, soil solution ratio, was found to be optimum. Good agreement was found between the proposed method and the standard neutral IN ammonium acetate leaching procedure with correlation coefficients (r) for the individual cations Mg, Ca, Na and K of 0.99***, 0.99***, 0.83*** and 0.96*** respectively. Strontium chloride extracted more Al but less Mn (P<0.01) than IN KC1, but because of the low levels of these cations in relation to the total cations present, there was still a good relationship (r= 0.99) between ECEC determined by 1.26M SrCl₂ and that determined as the sum of ammonium acetate extractable Mg, Ca, Na and K plus IN KCl‐extracted Al and Mn.     

Soil and plant calibration for cucumbers grown in the mid‐Atlantic coastal plain

Abstract

Few soil test and plant tissue calibration data exist for cucumbers (Cucumis sativus L.). Two years of a singly‐replicated cucumber fertility study were conducted to develop soil and plant data for calibration purposes employing the Boundary Line Approach. Fertility treatments consisting of 4 K levels (as KC1), 3 Mg levels (as MgCl₂), 3 pH levels (as Calcitic limestone), and 4 N rates (as urea ammonium nitrate) were factorilly arranged and completely randomized to give 108 treatments in both 1987 and 1988. Analyses were performed upon leaf samples for N, P, K, Ca and Mg at early bloom and soil samples for Mehlich (M) 1‐ and 3‐ P, K, Ca and Mg, and pH. Cucumber yields were determined on early (two fruit pickings) and total (four fruit pickings) sampling periods. High‐yielding cucumbers were attained at soil K (Ml = 64 mg/kg) and Mg (Ml = 29 mg/kg) levels lower than currently recommended. No significant differences in correlation coefficients between either Mehlich (Ml, M3) extractant and cucumber leaf P, K, Ca and Mg concentrations were found. Co‐efficients of determination (R²) values for the relationships (in 1987, 1988) between Ml‐ and M3‐extractable P (0.53, 0.40), K (0.77, 0.64), Ca (0.81, 0.71) and Mg (0.89, 0.74) were all highly significant (P ≤ 0.01). No significant differences were noted between early and total high‐yielding cucumber leaf concentrations and ratios developed for use as preliminary sufficiency ranges and DRIS norms, respectively. A reevaluation of cucumber coastal plain soil test calibrations, especially with regard to K, appears necessary. This study provides further support for the conversion of Ml to M3 soil extraction methodology.     

Cation exchange capacity measurements

Abstract

Soil cation exchange capacity (CEC) measurements are important criteria for soil fertility management, vaste disposal on soils, and soil taxonomy. The objective of this research was to compare CEC values for arable Ultisols from the humid region of the United States as determined by procedures varying widely in their chemical conditions during measurement. Exchangeable cation quantities determined in the course of two of the CEC procedures were also evaluated. The six procedures evaluated were: (1) summation of N NH₄OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus BaCl₂ ‐ TEA (pH 8.0) exchangeable acidity; (2) N Ca(OAc)₂ (pH 7.0) saturation with Mg(OAc)₂ (pH 7.0) displacement of Ca²⁺; (3) N NH₄OAc (pH 7.0) saturation with NaCl displacement of NH₄ ⁺; (4) N MgCl₂ saturation with N KCl displacement of Mg²⁺; (5) compulsive exchange of Mg²⁺ for Ba²⁺; and (6) summation of N NH₄OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus N KCl exchangeable AJ. The unbuffered procedures reflect the pH dependent CEC component to a greater degree than the buffered methods. The compulsive exchange and the summation of N NH₄OAc exchangeable cations plus N KCl exchangeable Al procedures gave CEC estimates of the same magnitude that reflect differences in soil pH and texture. The buffered procedures, particularly the summation of N NH₄OAc exchangeable cations plus BaCl₂ ‐ TEA (pH 8.0) exchangeable acidity, indicated inflated CEC values for these acid Ultisols that are seldom limed above pH 6.5. Exchangeable soil Ca and Mg levels determined from extraction with 0.1 M BaCl₂ were consistently greater than values for the N NH₄Oac (pH 7.0) extractions. The Ba²⁺ ion is apparently a more efficient displacing agent than the NH₄ ⁺ ion. Also, the potential for dissolving unreacted limestone is greater for the Ba₂ ⁺ procedures than in the NH₄ ⁺ extraction.     

Effect of soil pH and nitrogen source on nutrient status in peach: I. Macronutrients

Following 13‐year treatments of soil pH and nitrogen (N) source in a peach orchard of North Carolina, the concentration of calcium (Ca), magnesium (Mg), N, phosphorus (P), and potassium (K) in leaves, shoots, trunks and roots, as well as soil pH, soil exchangeable Ca, Mg, and K content, were determined. Through liming, higher soil pH treatment enhanced soil Ca and tissue Ca level. Among six N sources examined, the highest values of soil pH and soil Ca, Mg, and K were detected following poultry manure application. Compared to ammonium sulfate [(NH₄)₂SO₄], calcium nitrate [Ca(NO₃)₂] increased soil pH and soil Ca and K content, but reduced soil Mg. For most of macronutrients examined in peach tissues, the highest levels were found in manure treatment. Mineral N sources containing Ca(NO₃)₂ resulted in high tissue Ca and low tissue N. In the above‐ground tissues, Mg concentration was relatively low following application of mineral N materials containing Ca, K, or sodium (Na). Acid‐ forming N, especially (NH₄)₂SO₄, reduced tissue Ca and P. The magnitude of impact of liming and N source on macronutrients was tissue‐type dependent, with leaves and other new growth the most sensitive ones while trunks seldom responded to the treatments.     

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.     

Soil testing in the united states

Abstract

There has been a marked change in the soil testing procedures used in the United States by state soil testing laboratories since the early 1950's. In the Coastal Plain states of the south and east, the Double Acid extraction procedure is used for P, K, Ca, and Mg determinations. Bray P₁ is the most frequently used method for P extraction except for the alkaline soils of the west where the Olsen method is used. Neutral normal ammonium acetate is the most frequently used extractant for K, Ca, and Mg determinations. The Morgan extraction procedures for P, K, Ca, and Mg, commonly used in the 1950's, is used by only a few states in the northeast and west. Although similar extraction reagents are used in many sections of the United States, there is considerable variance among states regarding weighed versus volume sampling, soil to solution ratio, shaking speed and time, and extraction vessel size and shape. For soil water pH, there is little variance in method as most states are using a 1:1 soil to solution ratio. The only exception is in several western states where water pH's are read in a saturated soil paste.

Considerable efforts are underway to standardize the techniques used to test soils primarily for the extractable elements.     

Comparison of Prewashing Procedures for the Assessment of Phosphate Rock Dissolution in Soils

When evaluating phosphate rock (PR) dissolution, previous to the extraction with sodium hydroxide (NaOH), dry soil samples with PR were extracted with three solutions to remove exchangeable and solution calcium (Ca) [sodium chloride (NaCl) 1 M, buffered NaCl with ethylenediaminetetraacetic acid (EDTA) (NaCl–EDTA), and NaCl buffered at pH 7 with triethanolamine (TEA) (NaCl–TEA)] for comparison with the extraction of soil samples without any prewash. In acidic soils, up to 51% of applied P was recovered during the NaCl extraction because of the high exchangeable acidity released during the extraction. In soils with exchangeable Ca>2 cmol₍₊₎kg^?1, high EDTA quantities also promoted PR dissolution. The NaCl–TEA solution efficiently removed Ca, avoiding PR dissolution and P retention by calcium hydroxide [Ca(OH)₂] during the NaOH extraction. Thus, when evaluating PR dissolution we recommend the use of NaCl–TEA to remove Ca. We also recommend the same procedure when applying the Chang and Jackson fractionation to calcareous soils and soils submitted to PR application.