Determination of phosphate in solution at different ionic composition using malachite green

Abstract

The malachite green method was sometimes used to determine low concentrations of inorganic phosphate due to its high sensitivity. The aim of this work was to test the suitability of this method for the determination of phosphorus (P) extracted by various reagents, e.g., KCl 0.01–1.20M, CaCl₂ 0.01–0.1M, Na₂SO₄ 0.01–0.40M, NaHCO₃ 0.1M at pH 8.5, and NaOH 0.1M+NaCl 1M. The malachite green method was also compared with the traditional molybdenum blue method on 35 soil extracts. Color development reached stability within 2 hrs and was stable for up to 24 hrs for dilute solutions. For concentrated solutions the stability was inversely proportional to the concentration of the reagent. Salt concentration appeared to have no effect on absorbance in KCl extracts of up to 1.2M and in Na₂SO₄ extracts of up to 0.05M. Higher concentrations of sodium sulfate induced flocculation and precipitation of the dye complex, as did CaCl₂ above 0.04 M. A strong correlation was found between the malachite green and the molybdenum blue method. The malachite green method can be used for P determination in soil extracts when appropriate time of color development is provided and salt concentration is taken into account.     

Malachite green method compared to ascorbic acid for estimating small amounts of phosphorus in water, 0.01 M calcium chloride,and olsen soil extracts

Abstract

Malachite green method has been evaluated for estimating minute quantities of phosphorus (P) in water, 0.01M calcium chloride (CaCl₂), and Olsen [sodium bicarbonate (NaHCO₃)] extracts often soils of varying properties. The precision and accuracy of the malachite green method was better than that of the ascorbic acid method to estimate P in these three extracts. The recovery of added P ranged from 95.3–99.3% in water, 96–100% in 0.01M CaCl₂, and 96.7–100% in Olsen extracts. The ascorbic acid method underestimated the amounts of 0.01M CaCl₂‐P and its precision was also lower than the malachite green method. It is possible to predict the P concentration in the three extracts equal to malachite green method from the ascorbic acid P values by using regression equations.     

Sorption of Phosphorus from Swine,Dairy, and Poultry Manures

In most phosphorus (P) sorption studies, P is added as an inorganic salt to a predefined background solution such as calcium chloride (CaCl₂) or potassium chloride (KCl); however, in many regions, the application of P to agricultural fields is in the form of animal manure. The purpose of this study, therefore, was to compare the sorption behavior of dissolved reactive P (DRP) in monopotassium phosphate (KH₂PO₄)–amended CaCl₂ and KCl solutions with sorption behavior of DRP in three different animal manure extracts. Phosphorus single‐point isotherms (PSI) were conducted on eight soils with the following solutions: KH₂PO₄‐amended 0.01 M CaCl₂ solution, KH₂PO₄‐amended 0.03 M KCl solution, water‐extracted dairy manure, water‐extracted poultry litter, and swine lagoon effluent. The PSI values for the dairy manure extract were significantly lower than the CaCl₂ solution for all eight soils and lower than the KCl solution for six soils. The PSI values were significantly higher, on the other hand, for poultry litter extract and swine effluent than the inorganic solutions in four and five of the soils, respectively. Our observations that the sorption of DRP in manure solutions differs significantly from that of KH₂PO₄‐amended CaCl₂ and KCl solutions indicates that manure application rates based on sorption data collected from inorganic P salt experiments may be inaccurate.     

Berechnung des labilen Phosphats aus Phosphat-Pufferkurven (Q/I-Kurven)

Calculation of labile phosphate from phosphate buffer curves A procedure to calculate labile P from phosphate buffer curves (Q/I curves) is presented. It treats the buffer curves as Langmuir adsorption isotherms and calculates the labile P by extrapolation to zero. In a long term P fertilizer trial the labile P calculated in this way was nearly equal to the increase in plant available P as extracted by calcium lactate. From a heavily fertilized vineyard soil, on the other hand, more P was extracted by 3 · 10^?3 M CaCl₂ during the first extractions than calculated from the buffer curves whereas on further extractions the two quantities approached each other.     

Change Point in Phosphorus Release from Variously Managed Soils with Contrasting Properties

Abstract

Investigating the relation between concentration or release of phosphorus (P) into soil solution (CaCl₂‐P, determined by 0.01 M CaCl₂ extraction of soils) and soil test phosphorus (Olsen P, or 0.5 N NaHCO₃‐extractable soil phosphorus) for 10 widely ranging and variously managed soils from central Italy, a change point was evident where the slopes of two linear relationships meet. In other words, it was possible to distinguish two sections of the plots of CaCl₂‐P against Olsen P, for which increases of CaCl₂‐P per unit of soil test P increase were significantly (p<0.05) greater above than below these change points. Values of change point ranged from 14.8 to 253.1 mg kg^?1 Olsen P and were very closely correlated (p<0.001) to phosphorus sorption capacity of soils. Similar change points were also previously observed when Olsen P (and also Mehlich 3 P) of surface soils was related to the P concentration of surface runoff and subsurface drainage. Because insufficient data are available relating P in surface soils and amount of P loss by overland, subsurface, or drainage flow, using the CaCl₂ extraction of soil can be convenient to determine a change point in soil test P, which may be used in support of agricultural and environmental P management.     

Optimization of DTPA and calcium chloride extractants for assessing extractable metal fraction in polluted soils

Abstract

Metal availability in soils is often assessed by means of extraction with chemical solutions, among others the chelating agent DTPA (diethylenetriaminepentaacetic acid) and the non‐buffered salt calcium chloride (CaCl₂). The same procedures are used for polluted soils that were originally created to assess the nutrient status of arable soils. We studied the influence of various parameters (type of shaker, shaking time, soil to solution ratio, and concentration of chemical extractant) and modify the DTPA and CaCl₂ extraction procedures to make them suitable for the study of polluted soils. The chosen extraction ratio and extractant concentration were the followings: 8 g/20 mL of 0.1 MCaCl₂ and 2 g/20 mL of 0.005 M DTPA. The optimized procedures were applied to nine soil samples affected by different sources of pollution (mine works, vehicle emissions, and various industries). Cadmium (Cd) showed the highest extractability with both extractants. Depending on the soil, copper (Cu) and zinc (Zn) (using DPTA) and Cu and manganese (Mn) (using CaCl₂) were the followings in the extractable amounts. Cadmium, Cu, and Zn were highly correlated in both extractions and with total contents.     

Applicability of 0.01 M CaCl2 as a single extraction solution for the assessment of the nutrient status of soils and other diagnostic purposes

Abstract

The applicability of 0.01 M CaCl₂ solution as a single extraction agent for soils as a basis for fertilizer recommendation was tested on a variety of soils both from the Netherlands and from some tropical countries. Air‐dry soil samples were subjected to extraction with 0.01 M CaCl₂ and to several conventional extraction procedures, and the results were compared. In the soil suspensions pH was measured, whereas in the extracts Na, K, Mg, P, different extractable N‐forms and Zn were measured. The values found in CaCl₂ extracts are discussed in relation to results of other extraction procedures and as to their potential value in soil quality assessment. It is concluded that a single extraction procedure with 0.01 M CaCl₂ can be applied for fertilizer recommendation purposes. The possibility of determining different extractable N‐forms (NH₄, NO₃, soluble organic N) significantly enhances the value of the method in predicting the N‐fertilizer needs. Furthermore it was found that the concentration of Zn in 0.01 M CaCl₂ extracts was a good indicator of phytotoxicity in a polluted area. Additional advantages of this extraction are low costs, simplicity and repro‐ducibility.     

Chloride and carbonate salinity tolerance in Mimusops zeyheri seedlings during summer and winter shoot flushes

Shoot flushes alternate with root flushes and the evergreen red milkwood (Mimusops zeyheri Sond.) fruit tree has winter (May–July) and summer (October-December) shoot flushes in southern hemisphere. Fruit of this plant contain high vitamin C and the tree is being researched and bred for arid inland southern Africa regions. Climate change predictions suggested that by 2030 the regions would experience high temperatures (>45°C), recurrent floods and repeated droughts, which are associated with increased salinity challenges. The objective of this study was to determine the degree of salt tolerance in M. zeyheri seedlings to chloride and carbonate salinity during summer and winter shoot flushes under microplot conditions. Treatments, comprising untreated control, NaCl, KCl, CaCl₂ and Na₂CO₃ each at 1.0 molar (M) solutions, were applied weekly for eight weeks. During both seasons, CaCl₂ and Na₂CO₃ salinity had significant effects on soil pH and EC. During summer, salt types increased (106%–253%) dry shoot mass and reduced (53%–79%) root/shoot ratio. During winter, Na₂CO₃ salinity increased (114%) dry shoot mass, but the effects were not different to those induced by NaCl and CaCl₂ salinity. All other plant growth variables were not affected by salt type. Salt type had significant effects on assimilation of selected nutrient elements in leaf tissues of M. zeyheri seedlings during winter. Sodium chloride did not have significant effects on nutrient elements, whereas KCl, CaCl₂ and Na₂CO₃ significantly affected selected macronutrient elements and Zn. In conclusion, effects of chloride and carbonate salinity on M. zeyheri seedlings were both season- and salt type-specific, with seedlings displaying some degree of salt tolerance to chloride and carbonate salinity.     

Calibration of the single‐ and double‐buffer SMP lime requirement methods by root elongation bioassay

Abstract

Chemical and biological lime requirement (LR) reference values of 154 soils were obtained by six months of incubation of each soil with five levels of calcium carbonate (CaCO₃). Levels of CaCO₃ addition differed among soils according to their characteristics. Chemical LR values were based on the individual neutralization curves to achieve a desired pH (pH_d) value of 5.5, 6.0, and 6.5 in water or 5.0, 5.5, and 6.0 in 0.01M calcium chloride (CaCl₂). Biological LR values were estimated to achieve 90% relative root elongation on each soil after a growth period of 48 h using wheat cv Abe. Chemical values of LR suggest that SMP method is valid for a wide range of mineral soils from different geographic regions. However, the proportion of soil acidity reacting with the buffer is not constant. Results indicate that values obtained with the routine methods need to be calibrated with equations different from the originals. The use of curvilinear models to adjust one single pH of the soil‐buffer system improved substantially its accuracy, allowing the single‐buffer (SB) results to be comparable to the more time consuming and labourious double‐buffer (DB) technique. No advantage was noticed with the use of curvilinear equations for DB technique. The adoption of pH_d in 0.01M CaCl₂ leads to an increase of precision of the predicted LR. Regression equations are provided for calculating LR rates to different pH_d values. Accuracy is high (r²=0.887) even for pH values (5.0 in 0.01M CaCl₂) lower than normally considered in methods based on buffer solutions. An overestimation of biological LR values was observed with both SMP methods. Notwithstanding, a calibration can be also made with the root bioassay, adjusting the chemical values to lime rates based on biological constraints related with aluminum (Al) toxicity. Regression equations are provided. Once more, the use of quadratic model for SB method allows an accuracy (r²=0.836) comparable with the DB technique (r²=0.850).     

Phosphate adsorption by soils 1. Influence of time and ionic environment on phosphate adsorption

Abstract

The influence of reaction time and ionic environments, on phosphate adsorption were studied using one calcareous soil from India, and one calcareous and two latosols from Hawaii.

Phosphorus adsorption by soils has a initial rapid phase followed by a slow process. For plant nutrition studies, where emphasis is on P concentration of solutions from which plants derive P, isotherms should be constructed using data obtained after near‐equilibration has been attained. This condition does not obtain in a few hours and may require 6 days or more.

Calcium chloride as suspending electrolyte always gave lower phosphate solubility than when KC1 was used as electrolyte. Phosphate retention increased with increasing ionic strength. The necessity for obtaining clear supernatant solutions and the desirability for maintaining reasonable constant equilibrium conditions make 0.01 M CaCl₂ a reasonable choice for constructing P sorption isotherms, even though 0.01 M CaCl₂ is not representative of Ca concentrations in many soil solutions. Saturation extracts of soils investigated here were in the range 0.0002 to 0.005 M Ca.

Adsorption of calcium by highly weathered soils was high suggesting specific adsorption. Calcium adsorption was increased by phosphate additions to a Hydrandept.     

Evaluation of extractants for predicting availability of sulphur to mustard in inceptisols

Abstract

Mustard (Brassica juncea) is an important oilseed crop of northern India, which is widely grown in Delhi and adjoining States. This crop has a relatively high requirement of sulphur (S), and is sensitive to S‐deficiency. For predicting response of mustard to S application, several extractants have been tried with variable results. Since selection of a promising extractant for a particular soil needs careful consideration, the present investigation was planned to select the most promising extractant to predict the availability of S to mustard grown on Inceptisols of Delhi. For this purpose, a greenhouse experiment was conducted with twenty soils (two from each often important soil series from the cultivated alluvial soil belt of Delhi. Nine extractants, commonly used for estimating the availability of S, were evaluated and S in soil extract and in plant digest was estimated using the turbiditimetric method. The results indicate that the phosphate salt methods extracted comparatively more S than other extractants. The amount of S extracted by these extractants was found in the following order: KH₂PO₄‐500 ppm P>Ca(H₂PO₄)₂‐500 ppm P>0.001 M HCl>NaOAc+HOAc>heat soluble S>0.15% CaCl₂>l% NaCl> water soluble S>NH₄OAc+HOAc. Simple correlation coefficients of the amounts of S extracted by different extractants and the forms of S with the plant parameters were worked out. To determine the combined effect of soil characteristics on S extraction by different extractants, stepwise multiple regression analysis was carried out. Based on this study, the suitability of the extractants for mustard crops in Inceptisols of Delhi may be arranged as follows: 0.15% CaCl₂>water soluble S>0.001 M HCl>Ca(H₂PO₄)₂‐500 ppm>1%NaCl>NH₄OAc+HOAc>NaOAc+HOAc>KH₂PO₄‐500 ppm P>heat soluble S.     

Effects of salts on dry matter yield and nitrogen and phosphorus contents of rice plants

Abstract

The effects of different kinds and concentrations of salts on dry matter yield and nitrogen (N) and phosphorus (P) contents of rice plants under greenhouse conditions were determined for two silt loam soils, one from southern Ohio (Clermont) and one from Arkansas (Crowley). Yield and N and P contents tended to be enhanced by low salt concentration but to be depressed at higher concentration. The chloride salts (NaCl, CaCl₂) were most detrimental to yield and N and P contents, while the sulfate salts (especially Na₂SO₄,) were beneficial when the electrolyte concentration and P in the soil were not high.

The degree of adverse response to salts in the irrigation water and of favorable response to P fertilizer were reflected in the levels of electrolyte and available P in the soils studied. Total N content of the rice tissue increased much more from N and P additions than did total P content. The NaCl (1.5 mmhos/cm) and NaCl + Na₂SO₄ (3.0 mmhos/cm) salt treatments vere generally least detrimental, and NaCl and NaCl + CaCl₂both at 3.0 mmhos/cm were most detrimental to yield and N and P contents of tissue.

In the non‐lethal response range, salt‐depression of yield and N and P contents of tissue may well be largely or partially overcome by fertilizer application. In this study, the best combination of fertilizer and salt was the highest level of N (268 kg N/ha) and intermediate level of P (67 kg P/ha), in combination with NaCl + Na₂SO₄.     

盐胁迫下外源钙对高羊茅种子萌发和幼苗离子分布的影响

该文模拟了上海市临港新成陆地盐渍化土壤的盐分特点,并在100 mmol/L NaCl盐胁迫下,以常见牧草和草坪草高羊茅（Festucaarundinacea）为材料,在人工气候室可控制条件下,进行了盐胁迫下种子萌发和幼苗盆栽试验,用不同浓度的CaCl2（5、10、20、40、80 mmol/L）处理,研究高羊茅种子萌发和幼苗生长状况,重点研究了矿质元素Na^＋、K^＋、Ca^2＋和Mg^2＋在植株地上部分和地下部分的分布。研究表明：适当浓度的外源CaCl2浸种处理能缓解高羊茅种子受到的盐胁迫伤害,促使种子提前萌发,20 mmol/L CaCl2浸种处理能显著提高种子萌发率,但高浓度（80 mmol/L）的外源钙处理对高羊茅种子萌发不利;适当浓度的CaCl2处理能促进幼苗地上部分生长,降低高羊茅根冠比、稳定植物细胞膜、维持离子平衡、提高植物耐盐性,但是高浓度（80 mmol/L）CaCl2处理会对植物幼苗生长造成伤害。     

Extractability and adsorption of sulphate in soils

Virtually all of the indigenous sulphate (SO₄) in a range of UK soils with moderately high pH values (> 6) was found to be present in the soil solution and, as a consequence, was highly susceptible to leaching. For acid soils containing adsorbed SO₄, the extractability of SO₄ in NaCl and CaCl₂ solutions was dependent on both the ionic strength and cation species. Addition of small amounts (<～ 10^?2M) of either NaCl or CaCl₂ actually decreased the amount of SO₄ extracted, but SO₄ extractability increased sharply with concentrations of NaCl or CaCl₂ higher than about 0.1 M. At a similar ionic strength, more SO₄ was extracted by NaCl than CaCl₂. Sequential extraction with 1 M NaCl removed essentially all of the absorbed SO₄. The release characteristics of SO₄ were very different to those of phosphate and this difference in behaviour is not easily reconciled with the view that SO₄ is chemisorbed, as is phosphate. Except for a few acid soils with high oxide contents, the capacity of the soils to adsorb added SO₄ was quite small. None of the soils with pH values higher than 6 adsorbed a significant amount SO₄. The results raise questions regarding the efficiency of SO₄-containing fertilizers in correcting and preventing S deficiency in situations where leaching is important.     

Suitability of Extractants for Predicting Available Sulfur in Natural Grassland in the Inner Mongolia Steppe of China

Abstract

It was the objective of this study to compare the suitability of different extractants for predicting the availability of sulfur (S) in natural grassland in a sulfur response trial on three different soil types in the Inner Mongolia steppe of China. For soil analysis, seven different extractants have been employed. The inorganic SO₄–S concentration was determined by ion chromatography. Additionally, in the Ca(H₂PO₄)₂ extract the total soluble S was determined employing turbidimetry. Weak salt solutions (0.15% CaCl₂, Ca(H₂PO₄)₂, and KH₂PO₄) extracted similar amounts of SO₄–S. Extraction with 0.025 M KCl provided the lowest SO₄–S values. Deionized water dissolved significantly more SO₄–S in the control plots than most weak salt extractants. The concentration of soluble organic S decreased in the control plots after 100 days of plant growth, indicating that the organic S pool contributed significantly to the S nutrition of the forage crops. Significant relationships among the SO₄–S in the soil determined in different extracts and crop yield, sulfur content in the forage, and total sulfur uptake were only found for the Ca(H₂PO₄)₂ extract. In general, the correlation coefficients proved to be unsatisfactory for field experimentation.     

The determination of hot‐water‐soluble boron in some acid Oregon soils using a modified azomethine‐H procedure

Abstract

A method is proposed for determination of hot‐water‐soluble boron in acid soils from western Oregon. The soil sample is boiled in 0.02 M CaCl₂, filtered, and B determined using azomethine‐H. Soils extracted in this way yielded extracts with little color in them and the predicted error due to this color was 0.00–0.07 ppm B. The use of charcoal as a decolorizing agent resulted in comparatively high predicted errors.

Inductively‐coupled plasma emission spectroscopic (ICP) analysis of distilled water and 0.02 M CaCl₂ extracts indicated that the extractable B level was not affected by the presence of CaCl₂. Azomethine‐H yielded comparable values to ICP but the curcumin method tended to give high values for hot‐water‐soluble B.     

Extraction of soil phosphorus with calcium chloride solution for prediction of plant availability

Abstract

Soil and vegetative samples of ley and cereals were collected four times during the growing season from field and pot trials with different phosphorus (P) fertilisation levels. The soil samples, dried and of field moisture condition, respectively, were extracted by 0.01M calcium chloride (CaCl₂) at two different soil:extractant ratios (1:2 and 1:10), and analysed by inductively coupled plasma emission spectrometry (ICP) for content of P. The plant samples were digested in concentrated nitric acid (HNO₃) and the P content determined by ICP. Calcium chloride‐extractable P content was lowest in the middle of the growing season, while plant P was highest in the beginning of the season. Phosphorus extracted by CaCl₂ solution was higher at a soil:extractant ratio of 1:10 than at 1:2, and also when drying the soil before extraction. A soil:extractant ratio of 1:2 minimizes the risk of coming too near the limit of determination. However, if organic soils are also to be included, a ratio of 1:10 has to be used in order not to have all the solution absorbed by some types of soils. The solution of ammonium lactate/acetic acid (AL) extracted nearly two powers of ten more P than CaCl₂ solution. There was a good relationship between the methods. If calcareous or very acid soils had been included, a less good relation would have been expected. Plant P content varied more in straw than in grain between different treatments. Measuring CaCl₂‐extractable P with ICP might be able to predict plant uptake of P by plants. This would be a great advantage when using 0.01M CaCl₂ as a universal extradant.     

Soil Potassium‐Release Characteristics and the Correlation of its Parameters with Garlic Plant Indices

Abstract

Potassium (K)‐release characteristics (PRC) of soil play a significant role in supplying available K. Information about PRC in the Hamadan soils is limited. The objective of this research was to study the PRC in nine soils from the Hamadan province by successive extraction with 0.01 M CaCl₂ over a period of 2000 h. The correlation of kinetic equation rate constants with soil properties and garlic indices was also studied. The release of K was initially rapid. More than 60% of the total K released during the first 168 h. The amount of K released after 168 h varied among soils and ranged from 292.8 to 736.8 mg kg^?1. The amount of K released after 2000 h was significantly correlated with K extracted by 1 M HNO₃, 0.01 M CaCl₂, and 0.1 M BaCl₂, whereas it was not significantly correlated with other soil properties. Potassium‐release characteristics were evaluated using five kinetic equations. Statistical analysis showed that the Elovich equation described the K‐release kinetics. A plot of other equations shows a discontinuity in slope at 168 h. Thus, two equations were applied to segments of the total reaction time (2 to 168 and 168 to 2000 h). The release‐rate constants (slope) in segment 1 are higher than in segment 2. The release‐rate constant of the Elovich equation and the zero‐order equation in two segments were significantly correlated with 1 M HNO₃, 0.01 M CaCl₂, and 0.1 M BaCl₂. Rate constants of the other equations were not significantly correlated with soil properties. The release‐rate constants of the Elovich equation and release‐rate constants of the zero‐order equation in two segments were significantly correlated with garlic indices. Rate constants of other equations were not significantly correlated with garlic indices. The results of this research showed that the Elovich and zero‐order equations can be used to describe K‐release characteristics.     

Sulfur mineralization in sphagnum peat

Abstract

Open and closed incubation systems were studied as means of quantifying sulfate fractions in sphagnum peat moss. Sulfate was extracted in the closed system with a 0.15% CaCl₂‐H₂O or a 500 mg P/L extractant. Sulfate was extracted in the open system with 10 mM KC1, 0.15% , CaCl₂‐H₂O, or 500 mg P/L extractant. Extractants were quantified by ion chromatography. Phosphate extractant released more sulfate than CaCl₂, in the closed system. There was a significant increase over time of sulfate released by the CaCl₂ extractant. In the open system, there was no significant difference in release and total amounts leached of sulfate‐S between extractants. The closed system released more sulfate‐S than the open system. Phosphate extractants in both systems mineralized 43% of initial sulfur content