A modification of Douglas and Bremner method for colorimetric estimation of urea

Abstract

The use of H₃PO₄ in colorimetric estimation of urea by the method of Douglas and Bremner sometimes leads to wide batch variations. A modification of this method is proposed where H₂SO₄ only is used in place of H₃PO₄. The use of H₂SO₄ increased the linear calibration range almost two‐fold without affecting the precision of the original method. The developed color remains stable for 72 hours in the dark.     

Determination of total sulfur in soils and plant materials by ion chromatography

Abstract

An accurate and precise ion Chromatographie (IC) method is described for determination of total S in soils and plant materials. It involves ignition of a mixture of soil and NaHCO₃or plant material and NaHCO₃containing Ag₂O at 550°C for 3 h. The residue is dissolved in 1MHOAc, diluted with deionized water, filtered, and analyzed for S0^2‐ ₄by a Dionex model 2002i ion Chromatograph. Results by the IC method of seven Iowa soils, three Chilean soils, and 10 plant materials agreed closely with those obtained by the methylene blue method after alkaline oxidation with NaOBr. In general, the IC method was more precise than the methylene blue method. The method is simple and requires a minimum of analytical skill. A single operator can analyze 30–40 soil or plant samples in a normal working day.     

A rapid accurate wet oxidation diffusion procedure for determining organic and inorganic carbon in plant and soil samples

Abstract

A method is presented for determining organic carbon content of soils, extracts and plant tissue utilizing an acidic wet oxidation in modified culture tubes; samples containing carbonates are pretreated with dilute acid. Evolved CO₂ is trapped in a NaOH solution and quantified titrimetrically. The method described has a range of 0.4–11 mg. carbon and the range can be extended in either direction by modifying the CO₂ trapping/titration procedure. This method is as accurate and precise as more time consuming dry oxidation procedures.     

Comparison of the Ignition Method and the Perchloric Acid Digestion Method for the Determination of Total Phosphorus in Agricultural Soils of Taiwan

The ignition method and the perchloric acid (HClO₄) digestion method for the determination of total phosphorus (P) content in 65 agricultural soils of Taiwan were compared. The average amount of total P obtained by the ignition method was 4.3% less than that obtained by the HClO₄ method. There was a wide range of variation, from 37% less to 21% more in the ignition method than those results obtained by the HClO₄ digestion method. Because the ignition method can also be used for the estimation of soil organic P and is thus worthy of further study, it should be adopted as a routine procedure.     

石灰性土壤交换性钙和镁测定方法的研究

石灰性土壤交换性盐基组成的测定,通行的方法是采用70%乙醇溶液反复洗盐,再经pH 8.50.1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液进行多次交换处理,测定交换液中的K+、Na+、Ca2+、Mg2+浓度。但此方法常常受操作步骤繁琐,以及土壤中碳酸盐的溶解量因多次浸提而增加的困扰,最终导致测定结果偏高。基于上述原因,选择不同浓度、不同pH的NH4OAc和NH4Cl 10种交换剂,对比分析10种交换剂中的碳酸盐溶解度和土壤交换性钙镁含量。结果表明,pH=8.5 1 mol L-1氯化铵-70%乙醇(CH3CH2OH)溶液较适合石灰性土壤交换性盐基的测定。此新方法是先经70%乙醇(CH3CH2OH)溶液洗盐,再用pH8.5 1 mol L-1氯化铵(NH4Cl)-70%乙醇(CH3CH2OH)溶液进行一次性交换处理,然后测定交换液的K+、Na+、Ca2+、Mg2+浓度,简化了操作程序的同时有效抑制了土壤碳酸盐的溶解,降低了测定结果的偏差。     

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.     

Atmospheric Concentrations of Sulfur Dioxide and Nitrogen Dioxide in China and Korea Measured by Using the Improved Passive Sampling Method

The results of ambient sulfur dioxide (SO₂) and nitrogen dioxide (NO₂) concentrations measured in ten cities of China and Korea by the improved passive samplers are reported. The property of this sampler is the utilization for the long-term exposure to the high level of SO₂ and NO₂. In this method, the conversion coefficients from the analytical data to the ambient concentrations were obtained from the comparison with the direct concentrations through the automatic analyzers for SO₂ and for NO₂, respectively. The interesting monthly variations were observed in the ambient SO₂ and NO₂ concentrations measured by this passive sampler method, which seems to give important information to the formation of acid rain in these countries.     

Soil extractants used in Estonia and Finland,their extraction power,and suitability for testing Estonian soils

Abstract

The present work was undertaken to obtain information on the effectiveness of extractants used for soil testing in Estonia and in Finland and to evaluate the suitability of the Finnish methods for use with Estonian soils. The sample material involved 86 soils and winter wheat (Triticum aestxvum L.) shoots collected from farmers’ fields in Estonia. The extractants used in Estonia were double lactate (DL) for phosphorus (P) and potassium (K), ammonium lactate (AL) for calcium (Ca) and magnesium (Mg), 1N HCl for copper (Cu), manganese (Mn), and zinc (Zn), ammonium oxalate (AO) for molybdenum (Mo) and 1N HNO₃ for cadmium (Cd) and lead (Pb). In Finland, acid ammonium acetate (AAAc) was used for P, K, Ca, and Mg determination, and acid ammonium acetate‐EDTA (AAAc‐EDTA) for Cu, Mn, Mo, Zn, Cd, and Pb. The order of magnitude of extractable concentrations for these elements was: P_DL > P_AAAc, K_DL < K_AAAc, Ca_AL < Ca_AAAc, Mg_AL> Mg_AAAc, Cu_HCl > Cu_AAAc‐EDTA, Mn_HCl, > Mn_AAc‐EDTA, Zn_HCl < Zn_AAAc‐EDTA, Mo_AO > Mo_AAAc‐EDTA, Cd_HNO3 > Cd_AAAc‐EDTA, and Pb_HNO3 > Pb_AAAc‐EDTA. Correlations between results of respective methods for determining macronutrients were high (r ≥ 0.9). In the case of Cu, Mn, Mo, Zn, Cd, and Pb r values ranged from 0.5 to 0.8 due to difficulties in determining low concentrations. A statistically significant correlation between concentrations of elements in soil and in wheat shoots only existed for few elements. The DL extractable P and K correlated better than those for the AAAc method, and coefficients for the DL method were 0.29 and 0.31, respectively. This indicates that the DL method is better suited to Estonian soils than the AAAc method. In the case of Cu, Mn, Mo, and Zn, no method preference was found.     

A Rapid and Sensitive Determination Method for Soil Nitrate Status

A rapid and sensitive determination method for soil nitrate status is proposed using anion exchange high pressure liquid chromatography. The effect of different extracting solutions and elution-buffer pH is investigated on the determination of NO₂ and NO₃ in standard solutions and various soil extracts in the concentration range of 0–40 ppm. A high lineair correlation is obtained between results from both the Bremner distillation method (1965) and this anion exchange HPLC-method when compared on 69 soil samples. The sensitivity, reliability and ease of handling make anion exchange HPLC a valuable method for the determination of soil nitrate.     

Calibration and validation of four common ET0 estimation equations by lysimeter data in a semi-arid environment

In this study, four different methods for reference crop evapotranspiration (ET₀) were calibrated and validated for estimation of daily to mean monthly ET₀ by weighing lysimeter data during 2005–2006 and 2004–2005, respectively, in a semi-arid region. The value of the constant in the Hargreaves–Samani method changed from 0.0023 to 0.0026 for daily to mean monthly ET₀, and can be used in stations with only air temperature data. The constant of the aerodynamic resistance equation in the FAO-56 Penman–Monteith method (208.0) changed to 85.0. The value of coefficient a in the FAO-24-Radiation method was between ?0.5 and ?0.67. Further, the empirical equations were modified to estimate the value of b in the FAO-24-Radiation method and C in the FAO-24 corrected Penman method. The results showed that the modified FAO-56, corrected Penman–Monteith and FAO-24-Radiation methods are the most appropriate for estimating daily to mean monthly ET₀. Furthermore, the modified FAO-24 corrected Penman method was ranked in fourth place and its accuracy was lower than that of the other methods. However, it is appropriate for estimating mean monthly ET₀. Smoothing the daily data decreased the fluctuation in measured daily weather data and ET₀ measured by lysimeter, and consequently resulted in a higher accuracy in the estimation of daily ET₀.     

Effects of DEM horizontal resolution and methods on calculating the slope length factor in gently rolling landscapes

The USLE is used world-wide to predict soil loss on the field scale from sheet and rill erosion. The slope length (L) factor is derived as its topographical factor. The accuracy of L factor determines the precision of soil loss estimation with USLE. Uncertainties on L factor are caused by DEM resolution and the choice of the processing algorithm. In the present study we made two comparisons to evaluate the effects of DEM horizontal resolution and processing algorithm on the accuracy of the L factor in gently sloped landscapes: one is between the grid cumulating method (GC) and the contributing area method (CA) using D8 flow-routing algorithm, the other is among single (D8, Rho8) and multiple (FD8, FRho8 and DEMON) flow-routing algorithms for processing the contributing area method. In two comparisons, 5 m, 10 m, 25 m, 50 m and 100 m DEM of a 0.88 km² catchment in the lowland of Northern Germany were applied. The results indicate that L factor calculated with any of the six methods is sensitive to horizontal resolution, which strongly affects the accuracy. With decreasing resolution, correlations of L_{CA_Rho8} and L_{CA_D8}, L_{CA_FD8} and L_{CA_D8}, L_{CA_FD8} and L_{CA_Rho8} increase while those between DEMON and the other flow-routing algorithms do not change significantly. With decreasing resolution, the difference between L_{GC_D8} and L_{CA_D8} is enlarged, while differences between any two flow algorithms using CA did not change significantly. The L factor variation between any two methods is larger on the upslope than the flat valley for the 5 m and 10 m DEM while terrain characteristics are not visible on the 25 m, 50 m and 100 m DEM. The L factor also depends on the computation method. L_{GC_D8} is approximately half of L_CA. It is concluded that DEM horizontal resolution is very important for L factor calculation. The most suitable calculation method is L_{GC_D8} for gently rolling landscapes. This study can be used for selecting a suitable method and DEM resolution for accurate calculation of L factor and soil loss in gently rolling landscapes.     

Conversion of soil particle size distribution and texture classification from ISSS system to FAO/USDA system in Japanese paddy soils

ABSTRACT

The conversion between the two different systems, ISSS and FAO/USDA, of particle size distribution and soil texture classification is useful to characterize soil physical properties and usage of each published. The objective of this study is to test some functions that have been published for conversion from ISSS to FAO/USDA system for Japanese paddy soils and to select the best method. We tested the topsoils of 267 Japanese paddy fields using the log-linear method, log-normal method, multiple regression method, Skaggs et al.’s method, and Minasny and McBratney’s method. The least AIC was obtained using multiple regression method, and the equation derived was given as follows:

si_FAO/USDA = 1.305si_ISSS + 0.396fs_ISSS?0.100cs_ISSS ? 12.323

where si, fs, and cs are the percentage of silt, fine sand, and coarse sand respectively; ISSS and FAO/USDA is the fractionation system; and its RMSE was 3.1%. For the case that only the total sand content (s) is available instead of fine sand and coarse sand, the following equation was obtained:

si_FAO/USDA = 0.314si_ISSS + 1.533s_ISSS ? 20.903 (RMSE = 3.7%)

Among the non-empirical methods, the best estimation method was Skaggs et al.’s method, and its RMSE was 3.3%. The soil texture classification by FAO/USDA system using estimated particle size fractions by the above equation can be classified to correct categories. The accuracy ratio of the classification was 93-97%.     

Digestion of plants and organic soils using nitric acid,hydrogen peroxide and UV irradiation

Abstract

A two‐step digestion procedure using HNO₃ and H₂O₂/UV irradiation is described. The samples are predigested with HNO₃, succeeded by digestion in H₂O₂ under UV irradiation. The maximum temperature is 150°C. The digestion is performed without sample transfer during oxidation. The analytical data obtained by the new digestion method do not deviate from those obtained by HClO₄ digestion. The macronutrient elements including P were measured.     

Amino acid analysis of soils and sediments: Extraction and desalting

A convenient desalting method is described for removing interfering cations from hydrolysates of soils and sediments in preparation for Chromatographie separations of amino acids. The method is based on the retention of multivalent cations as their polyanionic fluoride complexes (SiF^2?₆. A1F^3?₆ and FeF^3?₆) on an anion exchange resin (F^? form). Recovery of amino acids is quantitative and the technique facilitates the determination of aspartic and glutamic acids without further chromatography. An HF pretreatment was required for maximum extraction of organic nitrogen from subsurface soils.     

A simple gas chromatographic approach to evaluate CO2 release,N2O evolution,and O2 uptake from soil

Summary We have developed a simple method for the determination of gaseous compounds that reflect microbial activity in soil, as affected by factors such as the presence of an organic amendment (peat) or a variation in soil moisture. The method is based on a gas chromatographic analysis of the headspace of vials containing the soil under examination. A single gas chromatograph can detect up to 10 different gases. As expected, after peat was added to the soil, CO₂ evolution and O₂ uptake increased significantly. Positive relationships were found between the evolution of N₂O, and soil moisture and the amount of peat added to the soil. Both the these variables influenced the CO₂:O₂ ratio. The results given by this method show high reproducibility.     

Digestion Methods for Total Heavy Metals in Sediments and Soils

The objectives of this study were to analyze the total contents of Cd, Cr, Cu, Ni, Pb, and Zn in the freshwater sediments and the arable and non-arable soils of Taiwan, and to compare the different digestion methods for their determination. Two hundred and thirty-nine freshwater sediments were collected from the Fei-Tsui Reservoir Watershed (FTRW) in northern Taiwan. Forty-two surface (0–15 cm) and subsurface (15–30 cm) soil samples were likewise collected from 21 representative arable soils derived from various parent materials and with varying weathered degrees in different regions of Taiwan. In addition, one hundred and ninety-four non-arable soils were collected from the different forest regions, industrial parks, resident areas, and commercial areas. Several digestion methods including the aquaregia and different combinations of concentrated acids (HClO₄, HNO₃, H₂SO₄, or HF) were compared. All samples were digested both by the aqua regia method and the Baker and Amacher method for Cd, Cr, Cu, Ni, Pb, and Zn. The Reisenauer method was used for Cr and the Burau method for Pb further. The results indicate that the best digestion methods to analyze the total contents of heavy metals in the sediments and soils were recommended as follows: the Baker and Amacher method for Cd, Cr,Cu, Ni, and Zn; the Reisenauer method for Cr, but for simplicity the Baker and Amacher method is also recommended as the flexible method for the total analysis of Cr; the aqua regia method for Cu, Ni, and Zn; and the Burau method for Pb.     

Vitamin D3: Preconcentration and Determination in Cereal Samples Using Ultrasonic‐Assisted Extraction and Microextraction Method

This research is the first analytical method to isolate and determine cholecalciferol (vitamin D₃) in cereal samples. Ultrasonic‐assisted extraction followed by dispersive liquid‐liquid microextraction as a fast, reliable, and highly sensitive method was employed for the preconcentration step. High‐performance liquid chromatography allowed an efficient and considerably faster analysis. Alcoholic KOH solution was employed for accomplishing the fast and easy release of vitamin D₃ from the wheat flour and bread matrix. Effective factors in the microextraction process were investigated and optimized with response surface methodology based on a central composite design. Under the best conditions, the calibration curves showed high levels of linearity (R ² > 0.999) for vitamin D₃ in the range of 2–500 ng/g. The relative standard deviation for the seven analyses was 6.2%. The relative recoveries of vitamin D₃ in spiked wheat flour and bread samples were 87–98%. The limit of detection and limit of quantitation were 0.7 and 2.1 ng/g, respectively. The method compared favorably with other methods for vitamin D₃ analysis of various foods.     

Combination of micro suction cups and time-domain reflectometry to measure osmotic potential gradients between bulk soil and rhizosphere at high resolution in time and space

A prerequisite to investigate the importance of osmotic potential (Ψ_o) in relation to matric potential (Ψ_m) in the soil for water uptake is the existence of a method that measures the temporal and spatial dynamics of Ψ_o in the vicinity of roots. One method for measuring Ψ_oin situ is the collection of soil solution with micro suction cups, the spatial resolution of which is suitable for rhizosphere studies. A major drawback of soil solution sampling is the disturbance of soil solution equilibrium, which makes frequent measurements impossible, so another method is required to provide information on the temporal dynamics of Ψ_o. The time‐domain reflectometry (TDR) technique might be suitable as the signal attenuation (σ) shows a close linear correlation with the salt concentration for a known soil water content. The temporal resolution of the TDR technique is high and the measurement has no impact on soil solution equilibrium. However, the spatial resolution of the TDR technique is too coarse to be used on its own in rhizosphere studies. We used a combination of TDR (fine temporal resolution) and micro suction cups (fine spatial resolution) to measure Ψ_o in a model system with Zea mays grown in quartz substrates. Osmotic potential changed continuously with time, and a steep gradient between bulk soil and the root compartment developed during the 39‐day growing period. The steepest gradient measured over a distance of 6 mm across the nylon net, separating the bulk soil from the root compartment, was ?365 kPa. The combination of both methods made it possible to extend the time interval between micro suction cup samplings and thus minimize the impact of sampling on soil solution equilibrium. Problems of separate calibration were avoided by calibrating the TDR measurements against the results obtained with the micro suction cups within the same experiment.     

Evaluation and calibration of simple methods for daily reference evapotranspiration estimation in humid East China

The current study aims to improve the performance of simple methods for the estimation of daily reference evapotranspiration (ET₀) in humid East China, namely Priestley–Taylor 1972 (P-T 1972), Hargreaves–Samani 1985 (H-S 1985) and Turc 1961 (TU 1961). These methods were evaluated and calibrated based on well-watered grass lysimeter experiments. The FAO-56 Penman–Monteith equation (FAO-56 PM) is the best method, and the radiation-based methods (TU 1961 and P-T 1972) perform much better than the temperature-based method (H-S 1985). In the simple methods, the coefficients are calibrated to: 1.34 for P-T 1972; 0.0186, 23.47 and 17.06 for TU 1961; and 0.0027 and 0.449 for H-S 1985. The locally calibrated TU 1961 and P-T 1972 perform much better than the original, with either the observed ET_0r or the ET_0c obtained by FAO-56 PM as standard. However, local calibration does not significantly improve the performance of the H-S 1985 method. In humid East China, FAO-56 PM is the best method for daily ET₀ calculation. TU 1961, especially if locally calibrated, is the optimal choice as a simple substitute for FAO-56 PM when solar radiation is available. Otherwise, serious local calibration is strongly recommended before applying H-S 1985 for daily ET₀ estimation.     

Estimation of the diffusion coefficients of adsorbed and non-adsorbed solutes in soil

A method is proposed which follows Darrah's experimental procedure and takes advantage of a mathematical solution provided by Carslaw & Jaeger to estimate the diffusion coefficients of adsorbed and non-adsorbed solutes in soil. The method requires only the values of the concentration of the solute at the input face of a uniform column of soil, C^s, and of the total amount, Q_t, that has entered the soil after a specified time during which the surface of the block is in contact with a thin porous pad containing a known initial amount of solute, Q₀, at concentration C₀, expressed in the same units as C^s. In the C^s/C₀ vs. Q_t/Q₀ space there is a unique relationship between the effective diffusion coefficient, D_e, of the solute in the soil and the contact conductance for this solute, h, between the pad and the soil surface. The proposed procedure is firstly to determine D_e, and h for a non-adsorbed solute in the experimental soil using the experimental values of C^s/C₀ and Q/_Q for that solute. This value of D_e, gives the diffusion impedance factor for the solute in the soil, f, which is assumed also to apply to adsorbed solutes. A first estimate of the effective diffusion coefficient of an adsorbed solute, ¹D_ea, is then made using f and the diffusion coefficient of the free solute in water, D_L, obtained from the literature (i.e. ¹D_ea= D_Lf). Only if the solute is weakly adsorbed will the values of C^s/C₀, and Q_t/Q₀ lie in C^s/C₀, vs. Q_t/Q₀, space as defined by ¹D_ea and the contact conductance, h. Instead a second space relating C^s/C₀ and Q_t/Q₀, is now constructed from nominated values of h and D_e, where D_e, is defined in terms of ¹D_ea, the adsorption coefficient, F , and the volumetric moisture content of the soil, θ. The position of the experimental values of C^s/C₀, and Q_t/Q₀ within this new space defines h and the actual D_e, and F of the solute as it diffuses and is adsorbed in the soil. The advantages and limitations of the method are discussed. In particular, the method assumes that the adsorption process is linear and reversible.