Comparison of Phosphorus Determination Methods by Ion Chromatography and Molybdenum Blue Methods

The suppressed ion chromatography (IC) and molybdenum blue methods were used to comparatively evaluate phosphorus (P) concentrations. Most of the P was more resistant to hydrolysis in ion chromatography as compared to the molybdenum blue method. However, P analysis by IC is more liable to be interfered than the molybdenum blue method because of the presence of high bivalent and trivalent metal ions. Polyvalent metal ions interfere with organic P hydrolysis or the release of P from colloids during P investigation, which leads to a difference of ortho-phosphate concentrations determined by IC and molybdenum blue methods. During the environmental samples analysis, the ortho-phosphate obtained by the IC method was usually less than that obtained by the molybdenum blue method.     

Evidence That Sulfur Deficiency Enhances Molybdenum Transport in Xylem Sap of Tomato Plants

ABSTRACT

The findings of an experiment using serially harvested young tomato plants grown in water culture are reported, showing the dramatic influence of sulfur status of the nutrient medium on transport of molybdenum in xylem sap. On average for the five harvests taken over a 14 d growth period, the molybdenum (Mo) concentration in the sap was approximately 11 times greater in the absence of sulfate in the nutrient medium. Restoring sulfate to the nutrient medium without sulfur (S) on day four of the experiment depressed the Mo concentration of the sap at the next harvest (taken three days later) to a value similar to that in plants receiving sulfate from the onset of the growth period and, similarly, raised the S concentration as well. Rates of transport of Mo as measured by root pressure exudates were slightly less spectacular, as S deficiency depressed the rate of exudation. The results support the concept that sulfate and molybdate compete for the same carrier and transport sites in uptake, and that sulfate deficiency leads to excess Mo uptake. The findings are of little consequence for plant cultivation, as plants are tolerant to elevated Mo concentrations, but are relevant to animal nutrition—particularly that of ruminants, which are susceptible to excess Mo and Mo-induced copper (Cu) deficiency.     

Comparison of methods to evaluate the sulphur status of soils

Abstract

The sulphur status of 98 soils was assessed using nine methods, some of which were designed to include mineralizable sulphur. A close correlation was found between various direct extraction methods all using phosphate, though the turbidimetric method of analysis appeared to overestimate soil S values. Extractions following short term incubation with cysteine correlated significantly with direct extraction methods indicating that the soil sulphate pool is directly related to the soil's ability to mineralize readily available organic S. In contrast, incubation with elemental S gave no correlation. A respirometric method following amendment with cellulose gave only a poor correlation with two other methods. A Neubauer plant bioassay was most closely correlated to Ca (H₂PO₄)₂‐extractable S, CaCl₂‐extractable S and to extractable S following incubation with cysteine. The value of the various methods for routine use is discussed.     

Determination of trace amounts of phosphate in water extracts of soils

Abstract

Two methods are described for determining water‐soluble phosphate in the range 0.5 to 10 μg P/l, using solvent extraction for the concentration of molybdenum blue. The manual shaking method had a precision of 0.02 μg P/l; the continuous extraction method, a precision of 0.05 μg P/l. The methods have been found suitable for measuring phosphate in water extracts of soils.     

Comparison of different methods for determination of phosphorus in calcium chloride extracts for prediction of availability to plants

Abstract

Soil samples, dried and in 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), by ion Chromatograph, and by two different molybdenum blue methods for content of phosphorus (P). There was a good relationship between the methods, although the different methods gave quite different P values. Phosphorus detected by the molybdenum blue methods included not only orthophosphates, and the values were influenced by method‐dependent factors like effect of temperature. The difference is important when studying the complex of P cycle in soil and its plant availability and stresses the need for a reliable method of detecting low amounts of orthophosphates in soil extracts. Plant samples, collected at the same times as the soil samples, were digested in concentrated nitric acid (HNO₃) and the P content determined by ICP. Linear regressions were performed with plant P as dependent on extractable P according to different methods. The degree of explanation is generally between 0.6 and 0.9, without indicating any method as superior in predicting plant availability of P.     

Evaluation of a rapid method for plant sap nitrate analysis

Abstract

A rapid method of analysis of nitrate in plant sap using Merck test strips was evaluated. Accuracy and precision of the strips was found to be acceptable in a test in which aqueous samples were tested by four operators. Nitrate N was measured in five vegetable crops at two stages of growth by two methods: squeezing sap from fresh petiole or stem tissue with NO3‐N determination by Merck test strip; and acetic acid extraction from dried petiole or stem tissue with NO3‐N determination by autoanalyser. The relationship between the two methods was found to be highly significant with coefficient of determination exceeding 0.82 in eight out of 10 cases (crops x sampling dates). When the strip results were corrected for moisture content the relationship with the laboratory method improved in most cases.     

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.     

The determination of phosphorus in Kjeldahl digests of plant material by automatic analysis

Abstract

A method is proposed for the determination of phosphorus in plant material using a modified Kjeldahl digestion and a Technicon Autoanalyzer. The procedure depends upon the formation of phosphomolybdate and its reduction to molybdenum blue by ferrous ammonium sulphate. The method enables the simultaneous determination of phosphorus and nitrogen on the same plant digest.     

Quick extraction and determination of potassium in fresh leaf sap and its use as a guide to potassium fertilization of canola,chickpea, and dwarf sunflower

Abstract

Two simple methods to extract potassium (K) from fresh plant tissues for use as possible quick K tests: i) freeze/squeeze in which the tissue is frozen, thawed and extracted by placement in a syringe, and ii) press in which the sap is extracted by crushing fresh leaves in a garlic press, were evaluated. The K concentration in the leaf sap extracted using the two methods was determined using a hand‐held ion selective electrode meter. Two separate growth chamber experiments were conducted to evaluate method performance. In the first experiment, the relationships of fresh leaf sap K with total plant K and with K availability in the soil were determined using canola (Brassica campestris var. Profit) and wheat (Triticium aestivum var. Biggar). In the second experiment, canola (Brassica campestris var. Profit), chickpea (Cicer arientinum), and dwarf sunflower (Helianthus) were grown on two soils low in available K with six rates of added K. The fresh leaf K extracted by the two methods and measured using portable ion selective electrode were well correlated with total plant K concentration at harvest, and also closely reflected the differences in K availability in the soil as indicated by soil extraction and rates of added K. Among the two methods, the press method using a hand‐held squeezing device is the simplest one. However, the freeze/ squeeze method may be a more suitable predictor of the K availability in plant tissue that is less succulent.     

Effects of deep placement of controlled-release nitrogen fertilizer on soybean growth and yield under sulfur deficiency

Sulfur (S) and Nitrogen (N) metabolisms in plants are interacted and it is known that S deficiency decrease N absorption and metabolism. In leguminous plants S deficiency also decreases N₂ fixation by rhizobia in the nodules. Deep placement of a controlled-release N fertilizer is a good method to provide nitrogen to soybean without inhibiting N₂ fixation; thus, it was hypothesized that this method is able to provide nitrogen effectively to sulfur-deficient soybean plants. In this study effects of deep placement of coated urea on S-N physicological interaction, growth and productivity in soybean plants were examined using pot experiments. Soybean plants were grown with sulfate concentrations of 30, 100, or 1000 μM, with or without deep placement of coated urea. Shoot weights at the developing stage were not affected by S deficiency. SPAD values of leaves during the flowering stage decreased with S deficiency and increased with the deep placement of coated urea. S deficiency decreased seed weight per plant at the harvesting stage, but this decrease was attenuated by the deep placement of coated urea. N and S content in shoots at the developing stage increased with the deep placement of coated urea, whereas in seeds, only the N content increased. N₂ fixation activity based on the relative ureide-N content in xylem sap indicated that the deep placement of coated urea did not inhibit N₂ fixation activity at the early flowering stage. Without deep placement of coated urea, the relative ureide-N content decreased under S deficiency at the seed filling stage. These results suggest that the deep placement of coated urea is an efficient method to supply N to support soybean yield under S deficiency.

Abbreviations: Deep+: with deep placement of coated urea; Deep–: without deep placement of coated urea     

Spectrophotometric determination of silicon in soil solutions by flow injection analysis: Reduction of phosphate interference

Abstract

A flow injection analysis (FIA) procedure for the determination of dissolved silica (0.04–20 mg/L Si) in aqueous solution has been optimized to reduce phosphate interference. Determinations are based on measurement of absorbance at 790 nm of heteropoly molybdenum blue formed by reduction with ascorbic acid at room temperature. Phosphate did not interfere in a 15‐fold excess. The optimized procedure was tested on soil solutions isolated by centrifugation of various horizons from a Typic Haplohumod. Si concentrations of 1.3–4.8 mg/L Si were found with a variation coefficient of about 2. Results obtained compared well with those obtained by a manual reference method and a proprietary FIA method except in solutions high in dissolved humic material where slightly higher values were obtained by the optimized method. In a standard addition mode the optimized method yielded 5–15% lower values than in the ordinary mode. This difference was reduced by persulfate oxidation of organic matter. Soil solutions investigated were very low in phosphate but phosphate spiking experiments demonstrated that phosphate interference was less than in model solutions matched in metal ion concentrations and insignificant in solutions low in humic material and with less than 10 mg/L P. Dissolved silica was unstable in a solution isolated from an organic horizon of high biological activity.     

Effects of air-drying on the adsorption and desorption of phosphate and levels of extractable phosphate in a group of acid soils,New Zealand

The effects of air-drying field-moist soils on the adsorption and desorption of added phosphate and on the levels of extractable native soil phosphate were examined using the A and B horizons of a group of four acid soils.Air-drying increased the capacity of all the soil samples to adsorb phosphate. At an equilibrium solution concentration of 0.5 μg P ml^?1, the increase in the quantity of phosphate adsorbed following drying ranged from 23% to 70% of that adsorbed by the moist samples. Considerable hysteresis in phosphate adsorption—desorption isotherms was observed for both moist and dried soil samples indicating that the additional phosphate adsorbed by the dried samples was held with the same strength as that held by the moist samples.Air-drying the soil samples caused a small decrease in soil pH of approximately 0.1 pH unit and a general increase in levels of EDTA-extractable Fe, Al and organic matter. Quantities of native soil phosphate extractable with EDTA, resin and NaHCO₃ were also increased. Concentrations of oxalate- and pyrophosphate-extractable Fe and Al and exchangeable Al were, however, unaffected by drying.It was also shown that when the phosphate content of NaHCO₃ extracts is measured using the conventional molybdenum blue method, orthophosphate plus a differing amount of acid-hydrolysable organic P present in the extract is measured.     

Quick nitrate test for hybrid sudangrass and pearlmillet Hays

Abstract

Hybrid sudangrass and pearlmillet are noted as having a high potential for accumulating nitrate (NO₃) and poisoning cattle. Hay samples can be accurately tested for NO₃ content in the laboratory, however, this may take considerable time for farmers to obtain their results. This study was conducted to evaluate applicability of a quick Nitrate Meter for in‐field testing of forage NO₃ in the plant sap and to study the effects of nitrogen (N) fertilization on forage NO₃ accumulation. Nitrate readings taken from the sap were highly correlated with those using the conventional laboratory method (R²=0.85–0.95 for hybrid sudangrass and 0.91–0.94 for pearlmillet). Nitrate concentrations varied with plant height, growing stages, locations in the test plots, N rates and sources, and environmental conditions. Nitrate concentrations in the whole plant decreased with plant height and plant maturity. Higher NO₃ levels were correlated with higher rates of N fertilizers. Nitrate accumulation was also enhanced by drought stress. The quick NO₃test method is easy to use and usually takes less than 20 minutes to obtain results. This methodology allows increased management flexibility for farmers who use warm‐season annual grasses in their production systems.     

Optimum Nitrogen Fertilization of Winter Wheat Based on Color Digital Camera Images

Abstract

Site‐specific nitrogen (N) fertilizer management based on soil N_min (soil mineral N) and the plant N status (sap nitrate analysis and chlorophyll meter (SPAD) reading test) has been shown to be effective in decreasing excessive N inputs for winter wheat in the North China Plain, but the multiple sampling of soil and plants in individual fields is too time‐consuming and costly for producers and farmers. In this study, a color digital camera was used to capture wheat canopy images at a specific growth stage to assess N needs. Treatments included a farmer's N treatment (typical farmer practice), an optimum N treatment (N application based on soil–plant testing), and four treatments without N (one to four cropping seasons without any N fertilizer input). Digital images were analyzed to get red, green, and blue color‐band intensities for each treatment. Normalized intensities of the red, green, and blue color bands were well correlated with soil N_min, SPAD readings, sap nitrate concentration, and total N concentration of winter wheat. This research indicated the potential of using a digital camera as a tool combined with an improved N_min method to make N fertilizer recommendations for larger fields.     

Spectrophotometric determination of phosphate in waters of Egypt

The proposed method is used for determination of trace amounts of phosphate in water samples especially of Dakahlia Governorate. The recommended procedure is based on the formation of molydophosphoric acid which upon, selective reduction with the reducing agent oxalyldihydrazide produces a blue color due to the molybdenum blue. The intensity of the blue color is proportional to the amount of phosphate initially incorporated in the heteropoly acid. The resulting blue complex could be determined in the range of 2.25 to 22.46 μg P with molar absorptivity of 33418 L^?1 mol^?1 cm^?1 at 880 nm. The reduction of phosphomolybdate complex by oxalyldihydrazide is chosen in the work and the result is compared with those obtained with the reducing agent potassium antimonyl tartrate, the reduction methods are frequently recommended for manual analysis of waters and wastes for P.     

Effect of restricted supply of nitrate on fruit growth and nutrient concentrations in the petiole sap of tomato cultured hydroponically

Tomato plants (Lycopersicon esculentum Mill. cv. Momotaro) were cultured in nutrient solution supplying 35 meq or 50 meq of nitrate (NO₃) per plant weekly from the flowering stage of the first truss in two cropping seasons. The effects of NO₃ supply levels and cropping season on fruit growth of tomato were investigated. Furthermore, the relationship between the results of the plant sap analysis and fruit growth of tomato was analyzed. In the spring to summer cropping, NO₃ supplied was almost all absorbed and high productivity of tomato fruits was obtained in each treatment. In the fall to winter cropping, however, high NO₃ supply did not increase the uptake of NO₃, but tended to decrease the rate of fruit set and marketable yield. Accumulation of NO₃ in the petiole sap was found with high NO₃ supply in the fall to winter cropping. Cropping season greatly influenced not only fruit growth but also the concentration of NO₃ in the petiole sap in relation to the ability of tomato plants to use available nitrogen (N). Furthermore, reduction in the rate of fruit set and weight of tomato fruit were found to relate to the low concentration of NO₃ in the petiole sap of the leaf just below this fruit truss. High NO₃ supply tended to increase potassium (K) concentration and electrical conductivity (EC) value, and to decrease phosphate (P), calcium (Ca), and magnesium (Mg) concentrations in the petiole sap. On the whole, concentrations of these elements in the petiole sap consistently reflected their uptake rates in two cropping seasons.     

Comparison between analytical results of plant sap analysis and the dry ashing method for tomato plants cultured hydroponically

Tomato plants (Lycopersicon. esculentum Mill cv. Momotaro) were cultured in nutrient solutions of varying concentrations or of varying nitrate (NO₃) levels. The leaf blades and the main petioles including rachis were collected from the mixture of three successive leaves below each fruit truss at two growth stages. Comparisons were made between the nutrient concentration in the leaf blade and the petiole determined by plant sap analysis, and that in the leaf blade determined by the dry ashing method. Closely correlated relationships were found to exist between the phosphorus (P), calcium (Ca), and magnesium (Mg) concentrations in the leaf blade and the petiole determined by plant sap analysis, and those in the leaf blade determined by the dry ashing method at two growth stages. For the concentration of potassium (K), there was no correlation between results of plant sap analysis and those determined by the dry ashing method at either growth stage.     

Phosphorus determination in rice plants containing variable manganese content by the phospho‐molybdo‐vanadate (yellow) and phosphomolybdate (blue) colorimetric methods

Abstract

Phosphorus (P) determination by the phosphomolybdate‐blue (Mo‐blue) and phosphomolybdate‐vanadate‐yellow (vandate‐yellow) color methods using NH₄OH to neutralize excessive acidity were unaffected by increasing manganese (Mn) content in standard P solutions and rice plant acid digests. The vanadate‐yellow color method using sodum hydroxide (NaOH) to neutralize excessive acidity over estimated P when the Mn content exceeded 0.16 Hg/ Mn/mL in the final dilution of standard P solution and 247 fig Mn/g in rice plant tissue. Phosphorus determination by the vanadate‐yellow color method using ammonium hydroxide (NH₄OH) was linearily related with P estimated by the Mo‐blue color and vanadate‐yellow color methods using NaOH for acid neutralization. Phosphorus estimated by the vanadate‐yellow color method using NH₄OH could be calculated from the a regression between both methods of neutralizing the excessive acidity.     

Sap analysis for diagnosis of nitrate accumulation in cereal forages

Abstract

Development of a quantitative, preharvest quiektest for NO₃ levels in cereal forages would improve crop management options to avoid NO₃ toxicity in livestock. Our objective was to determine if concentrations of NO₃ in sap expressed from oat (Avenasativa) and barley (Hordeum vulgare) are correlated with those in dry tissue of simultaneously harvested hay, and to test the reliability of the Cardy portable NO₃ meter for sap analysis in these species. In 1993, whole plant samples were gathered from plots fertilized with variable nitrogen (N) rates at four environments in Montana, and were analyzed for NO₃ concentration in lower‐internode sap and in whole plant dry matter. In 1994 and 1995, the study was repeated at two environments. The sampling technique included three subsamples from each plot for sap analysis, followed immediately by harvest of the entire plot for hay, and further subsampling for dry matter NO₃ analysis after drying. Linear correlations between dry matter and sap NO₃ concentrations were found across species at each environment in 1993 with r values of 0.64 to 0.81. No relationship was established for oat at one environment. Locations differed in the coefficient of correlation, indicating environmental influences on the relationship and/ or variability due to sampling technique. In 1994 and 1995, each species fit a separate linear correlation across site‐years with r values of 0.89 (oat) and 0.87 (barley). The consistency across site‐years (1994–1995) indicates that the variability in preliminary results was overcome with sampling technique. We propose a quantitative quiektest for NO₃ levels in cereal forages using conditional predictions of dry matter NO₃ based on observed values of sap NO₃. Since sap NO₃ readings with the Cardy portable nitrate meter were well correlated (r=0.93) with Accumet ISE readings across critical ranges, quiektest procedures are practical.     

不同镁浓度对水稻根系生长及生理特性的影响

在温室条件下, 采用溶液培养法研究了不同Mg2+ 浓度对水稻(Oryza sativa L.)根系生长及生理特性的影响。结果表明,水稻根系干重、根冠比、总根长、Mg吸收、根系活力、伤流速度、伤流液中游离氨基酸总量和Mg含量、Mg流入速率以及Mg2+ 吸收速率与Mg2+ 供应水平密切相关。在低Mg2+ 浓度(0.05 mmol/L)条件下,水稻植株叶片在缺Mg症状出现之前分配较大比例的干物质到根系,使总根长和根冠比增加, 这可能是水稻早期对低Mg胁迫的适应机制之一。适中的Mg2+ 浓度(1.0 mmol/L)有利于水稻生长发育,促进养分吸收,提高根系活力和伤流速度以及伤流液中游离氨基酸总量。低Mg2+ 和高Mg2+ 浓度(5.0 mmol/L)在一定程度上抑制根系活力和氨基酸合成能力。植物Mg的吸收、伤流液Mg2+ 浓度、根系平均Mg流入速率和Mg2+ 吸收速率随营养液Mg2+ 浓度的增加而相应增加。