The determination of ammonium and chloride by an auto‐analyser for the measurement of cation exchange capacity of soils

Abstract

An auto‐analyser method has been developed for the simultaneous determination of NH₄ ⁺ and Cl^‐ in Ca(NO₃)₂/KNO₃ extracts of NH₄Cl treated soils for cation exchange capacity measurements. The method gives satisfactory agreement with manual titration procedures.     

Can an isotopic method allow for the determination of the phosphate‐fixing capacity of soils?

Abstract

This work was undertaken to determine the ability of an isotopic exchange kinetics method to measure the fixation of P by soils. The parameter, Pfix, the ratio of introduced carrier‐free ³²P over ³²P remaining in solution after one minute of exchange, was determined on a wide range (n = 127) of samples from surface horizons of temperate and tropical soils. Pfix was compared to two parameters derived from adsorption isotherms, the maximum quantity of adsorbed P (Pmax) and the quantity of P to be adsorbed to reach a concentration in solution of 0.2 mg P/L (Po.2). Results showed that Pfix was at least as good as Pmax and Po.2 to estimate the soil fixing capacity. Pfix was correlated to the clay and iron oxide (Fed) contents, and highly significant correlations with Fed were observed for Pfix than for Pmax or Po.2. The isotopic exchange kinetics method can be recommended to determine the soil phosphate fixing capacity. Moreover, because of its accuracy and the minimal disturbance of the soil‐solution equilibrium, the method could be used for routine analysis of soil P‐fertility status.     

Chelating resin method for estimation of sludge‐cadmium bioavailability

Abstract

A chelating resin procedure was developed to predict the plant uptake of Cd by municipal sewage sludges applied to land. Seventeen anaerobically digested sludges were sampled to give a range of total Cd content of 0.07 to 2.02 mmol/kg. Sludge suspensions [20 g in 100 mL 0.05 M Ca(NO₃)₂] were equilibrated with 1 g Chelex 100 resin placed in dialysis tubing and shaken at 200 rpm for 16 h. Resin‐extractable Cd was compared with sludge solution Cd (CdT and Cd²⁺) in equilibrium with 0.05 M Ca(NO₃)₂, and 0.05 M Ca(NO₃)₂ containing 50 (μM Na‐EDTA (ethylenediaminetetraacetate). Resin extractable Cd was correlated with Cd uptake by sudax, a sorghum/sudangrass hybrid (Sorghum bicolar), grown in Spinks loamy sand (Typic Udipsamment) amended with each of the sludges to give a constant Cd concentration of 22 μmol/kg soil.

Resin extractable Cd ranged from < 0.1 to 48 μmol/kg. Resin extracted between zero and 5.3% of total sludge Cd. Resin extractable Cd was highly correlated with CdT and Cd²⁺ in 0.05 M Ca(NO₃)₂ (R² = 0.97 and 0.98, respectively), and with 0.05 M Ca(NO₃)₂ containing 50 μM NaEDTA (R² = 0.97 and 0.98, respectively). There was a lower correlation with total sludge Cd and soil solution Cd (R² = 0.53 and 0.63, respectively). Cadmium concentration in sudax was highly correlated with resin extractable sludge Cd (R² = 0.92). When the two sludges with highest total sludge Cd were dropped, the correlation dropped (R² = 0.57), but resin extractable Cd predicted Cd uptake as effectively as CdT and Cd²⁺ in Ca(NO₃)₂ or Ca(NO₃)₂/EDTA. Resin extraction appears to be a promising method of assessing the potential bioavailability of sludge Cd.     

Improved method for field‐scale measurement of ammonia volatilization

Abstract

We developed a new method for determination of atmospheric ammonia (NH₃) emissions from land‐applied nitrogen (N). The new method is a modification of two proven passive flux methods, and is an improvement over these existing methods via reductions in cost, labor and analytical requirements. This new method involves use of one rotating mast placed in the center of a circular plot (15 m radius). The samplers we use are glass tubes (7 mm by 200 mm) that have been coated on the inside with oxalic acid to trap NH₃. This new method was tested against one of the proven methods in a field experiment. A circular plot (15 m radius) was established and urea was applied to supply 200 kg N ha^‐1. Measurements of NH₃ volatilization were then made for six days after application. A strong linear relationship was evident between our new method and the reference method for both horizontal and vertical NH₃ fluxes, as indicated by correlation coefficients of 0.92 and 0.86 for horizontal and vertical fluxes, respectively. The glass tubes that we used consistently absorbed more NH₃ and measured more total NH₃ volatilization than the samplers of the reference method. However, given that micrometeorological methods have underestimated NH₃ volatilization in the past, we feel that our method has improved the accuracy of NH₃ volatilization measurement. In essence, we believe we have developed an improved method for field‐scale determination of NH₃ volatilization by reducing initial costs as well as labor and analytical requirements, without sacrificing accuracy of the volatilization measurement.     

Role of root cation‐exchange capacity in differential aluminum tolerance of lotus species

Three experiments were conducted in which roots of two species of Lotus were immersed for up to 40 min in complete nutrient solutions containing 6, 15 or 25 μM Al. The two species tested were L. pedunculatus cv. Grasslands Maku (Al‐tolerant) and L. corniculatus cv. Maitland (Al‐sensitive). There was an initial rapid (< 5 min) decrease in solution Al at 25 μM Al. The effect was less marked with solution Al ≤ 15 μM. The decrease in solution Al was greater in the Al‐sensitive Maitland than in the Al‐tolerant Grasslands Maku, particularly when expressed on the basis of root fresh mass and root length. Root cation‐exchange capacity (CEC) was lower in Grasslands Maku than in Maitland, viz. 23.9 vs 36.5 mmol kg^‐1 dry mass. Maitland roots removed more Al from solution than did those of Maku on the basis of total exchange capacity.

We propose a mechanism of Al tolerance on the basis of the results of this study and of other published information, viz. that differential Al tolerance results from differences in root CEC. Aluminum‐tolerant genotypes have roots with low CEC, and high Al activities (> 20 μM in the case of Grasslands Maku) are required to precipitate the relatively highly methylated pectins associated with low CEC. In contrast, relatively low activities of Al would precipitate the pectins in plants with roots of high CEC. This would decrease the protective capacity of the pectins, enabling the toxic, monomeric Al ions to come in contact with a number of Al‐sensitive compounds or processes in the cell wall, plasmalemma, or cell cytoplasm.     

Acidiphily in pteridophytes: Assessment of the role of root cation‐exchange properties

The soil preference with respect to soil acidity of Asplenium scolopendrium L., Dryopteris filix‐mas (L.) Schott, Pteridium aquilinum (L.) Kuhn as well as of subspecies of the Asplenium trichomanes L. and Polypodium vulgare L. complexes were studied in relation to root cation‐exchange properties. Data were collected for substrate acidity, soil exchangeable cations, and root cation‐exchange capacity. Acidiphilous pteridophytes were characterized by low cation‐exchange capacities. It is unlikely that cation‐exchange properties protect plants from potentially harmful cations such as aluminium or hydrogen, which are abundant under acid soil conditions, through immobilization. It is postulated that cation‐exchange properties are a secondary adaptation to soil acidity, in addition to major adaptations which determine the apparent soil preference. Possibly, a limited variation in cation‐exchange capacity as a function of soil conditions could prevent harmful interactions of soil exchangeable cations with the cation‐exchange sites, such as displacement of cell wall calcium by aluminium or hydrogen ions in acid soils.     

Participation of silicon in cation‐anion balance as a possible mechanism for aluminum and iron tolerance in some gramineae

Abstract

Silicon (Si) has been suggested as a factor in aluminum (Al) tolerance of some species of the gramineae when grown on acid soils. Silicon concentrations are generally much higher in monocot plants than in dicot plants, and the phenomenon is related to the fact that mineral cation:mineral anion uptake ratio is much higher in dicots than in monocots. When large amounts of anionic Si, supposedly as sulfate (SO₄ ^4‐), participate in cation‐anion balance to add to the excess of anion uptake, equivalent amounts of hydroxyl ions should be expelled from roots which can increase rhizosphere pH and decrease uptake of Al and iron (Fe). The magnitude of OH^? released by roots for a 5000 kg/ha crop with an excess uptake of 1% Si can be equivalent to 357 kg lime per hectare. This could be very significant in decreasing Al and Fe uptake from acid soils when localized in the rhizosphere. Success of agriculture on highly acid soils may be enhanced by use in a rotation of crops and cultivars that have the ability to accumulate Si.     

A new soil test method for the determination of plant‐available cadmium in soils

Abstract

A new soil test procedure using 1M NH₄Cl was developed for the extraction of plant‐available cadmium (Cd) from soils. Five grams of soil is weighed into a 50‐mL polyethylene vial to which 30 mL of 1M NH₄Cl solution is added. The soil suspension is then shaken on a horizontal shaker for 16 h at 25°C at 180 cycles per min. The suspension is then centrifuged at 2,500g for 5 min and the supernatant filtered through a 0.45 μm nitrocellulose filter under vacuum. Cadmium in the extract is then determined at 228.8 nm on a graphite furnace equipped atomic absorption spectrophotometer. A highly significant correlation was observed between the natural logarithm (In) of 1M NH₄Cl‐extractable Cd in soils and the Cd content in the grain of durum wheat (Triticum turgidum var. durutn L.) grown on the same soils (r = 0.974, p = 3.8 x 10^‐7). In comparison with several commonly used extradants, such as ABDTPA, CaCl₂, NH₄OAc, and NH₄NO₃, the 1M NH₄Cl‐extracted Cd from soils was found to be a better index of Cd availability.     

Effective cation exchange capacity of manure compost of varying maturity stages determined by the saturation‐displacement method

Abstract

The effective cation exchange capacity (ECEC) of manure composts, at the start and during the composting process, were determined. During this study we developed a new saturation‐displacement principle based method for compost samples. It was clearly demonstrated that ECEC of manure compost, as analyzed from three successive composting series, profoundly increased as compost matured. In addition, the ECEC values were highly repeatable, due to the proper mixing of the matrix with the saturation, washing, and displacement solutions, as well as to the preventing of any matrix losses with the separation of the matrix from those solutions with careful centrifugation‐filtration procedure.     

Washing procedure for mixed‐bed ion exchange resin decontamination for in situ nutrient adsorption

Abstract

Mixed‐bed cation + anion exchange resin bags are frequently used to assess in situ nutrient availability in forest soils, and have demonstrated their utility for comparing the impacts of different disturbances associated with treatments. They are generally installed in organic or mineral soil horizons for a certain time period, then recovered and extracted, to inform about nutrient availability during that period. For the method to be effective, the ion exchange sites of resins must be clear from any contaminants prior to installation in the soil. A washing procedure to be conducted before in situ burial of mixed‐bed resins was developed and is described. The IONAC NM‐60 H⁺/OH^‐ resins are consecutively washed with 2 N NaCl, deionized water, and 0.1 N NaOH. Finally, resins are rinsed with deionized water and stored moist and cold until bag preparation and burial in the soil.     

The effects of biocidal treatments on metabolism in soil—V: A method for measuring soil biomass

A new method for the determination of biomass in soil is described. Soil is fumigated with CHCl₃ vapour, the CHCl₃ removed and the soil then incubated. The biomass is calculated from the difference between the amounts of CO₂ evolved during incubation by fumigated and unfumigated soil. The method was tested on a set of nine soils from long-term field experiments. The amounts of biomass C ha^?1 in the top 23 cm of soil from plots on the Broadbalk continuous wheat experiment were 530 kg (unmanured plot), 590 (plot receiving inorganic fertilizers) and 1160 (plot receiving farmyard manure). Soils that had been fallowed for 1 year contained less biomass than soils carrying a crop. A calcareous woodland soil contained 1960 kg biomass C ha^?1, and an unmanured soil under permanent grass 2020. The arable soils contained about 2% of their organic C in the biomass; uncultivated soils a little more—about 3%.     

AB‐DTPA cation extraction in Spanish soil samples

Abstract

Since only one extraction is required to determine a large number of nutrients, many laboratories employ universal extractants to determine the available nutrients in a soil sample. This paper compares the universal ammonium bicarbonate‐DTPA (AB‐DTPA) method developed by Soltanpour and Schwab (1977) with the traditional methods, ammonium acetate (NH₄OAc) test for exchangeable cations and the Lindsay and Norwell (1969) test for the micronutrients. Results from the analysis of 28 soils by these methods were compared. Most soils were selected from those used by the Spanish Working Group for the Standardization of Analytical Methods. In most cases, statistical correlations between methods presented good agreement for each element, but depending on the soil pH range, some elements needed two correlations. Also, when results for wet and dry soils were compared, variability was lower when the AB‐DTPA extraction method was used. We concluded that, besides being faster, the AB‐DTPA method is valid for Spanish soils, even for calcium (Ca) extraction in calcareous soils, where the ammonium acetate method fails due to excessive Ca solubilization.     

Evaluation of an anion‐exchange membrane for extracting plant available phosphorus in soils

Abstract

Anion‐exchange resins (AER) have been used to determine plant available phosphorus (P) since the fifties and their results have shown strong relationships with plant growth and P uptake irrespective of soil properties. However, this procedure is still not widely used by laboratories because of difficulties in handling resin beads under routine conditions. New kinds and different shapes of resins are being produced each with specific characteristics that must be evaluated before use in laboratory procedures. Thus the objective of this work was to evaluate an AER manufactured in membranes reinforced with a Modacrylic fabric. These anion‐exchange membrane (AEM) sheets are commercially available, making them suitable for soil testing. The membranes were cut in pieces (1.0×7.5 cm) identified as AEM‐strips. The AEM‐strips were soaked in 0.5M HCl for a few days and transferred, after being rinsed with deionized water (DI), to 0.5M NaHCO₃ to convert them to HCO₃ ^‐ form. The AEM‐strips and resin beads in nylon bags recovered 98.4 and 98.0% of the P content in an aqueous P solution, respectively. Three eluent solutions were evaluated with different shaking times. The 0.1M H₂SO₄ and 1.0M NaCl in 0.1M HCl were equally suitable for the molybdenum blue color development without any pH adjustment, while the pH of the 0.5M HCl was too low. The elution of P from the AEM‐strips was independent of time with a 15‐min shaking being adequate for removal of all P from the strips. A comparison of soil sample preparation demonstrated that it was not necessary to vigorously grind or sieve the soil to improve the repeatability of the results. The AEM‐strips were compared with other methods (Pi impregnated filter paper, Mehlich I and Bray 1) using 32 soils from Guatemala with widely varying physico‐chemical and mineralogical properties. Phosphorus extracted by the AEM and Pi procedures (similar principle) were highly correlated and gave similar results irrespective of soil type. The acid extraction (Mehlich I and Bray 1 methods) attacked soil components (apatites) resulting in higher and inconsistent amounts of P extracted which may not be available to plants; the correlation between these methods within soils of similar properties was good, but when all soils were considered together the relationship was not significant. This demonstrated that the acid extraction method for P is not suitable for soils containing apatites, while those based on a sink for P (AEM and Pi) can be applied irrespective of the type of soil.     

Short‐term evolution of phosphorus in an ultisol

Abstract

Evolution of residual phosphate was monitored as function of time on an Ultisol without cropping in a field trial at Sembawa Rubber Research Station, South Sumatra, Indonesia. Three treatments were imposed and either triple superphosphate at a rate of 600 kg ha^‐1 containing 21.54% phosphorus (P) or lime at the rate of 4.14 tons ha^‐1 was applied. During the 20 months of incubation, extractable phosphate as evaluated by hydrochloric acid‐ammonium fluoride (Bray‐I) declined in all treatments. The decrease in the P fertilized plot was more pronounced in relation to the control and the limed soil. Only 56% of P added to the soil was initially recovered as extractable P. This percentage was 30–40% in limed soils. No significant pH difference was recorded for all treated plots except for limed soils. An increase of 1.3 pH units was initially obtained by liming, but the pH dropped to about 0.9 unit after 20 months of incubation. In addition, total P in arable layer remained fairly constant. According to the recoveries of P added referring to 4.3 P 100 g^‐1, half‐life of a single P dose was estimated at 31 months for a P fertilized soil and almost threefold delay for combination of P fertilization and lime application, which was obtained from the following equation:     

Evaluation of methods for determining sulphur‐35 and sulphur‐32 in the same trapping solution of Johnson and Nishita method

Abstract

A laboratory study was conducted to investigate whether the Zn‐Na acetate solution, used for trapping H₂S in the Johnson‐Nishita method (1952), could be used to quantitatively determine ³⁵S and ³²S in the same trapping solution, as the Zn‐Na acetate solution allows more sensitive S determination using methylene blue than does the bismuth sulphide colour development of H₂S trapped in NaOH solution. Results obtained using the Zn‐Na acetate solution were variable compared with those obtained from the normal procedure of using NaOH as the H₂S trapping solution, indicating that the Zn‐Na acetate solution was unsuitable, probably because of the rapid transformation of H₂S to water‐insoluble ZnS.

The applicability of methylene blue development for H₂S trapped in NaOH solution was also investigated. Results showed that ³²S could be determined quantitatively provided methylene blue colour development was conducted less than 30 minutes after the removal of H₂S‐trapping NaOH solution from the Johnson‐Nishita digestion‐distillation unit. A delay of more than 30 minutes caused a significant linear reduction (R² = 0.86 ‐ 0.92***) in methylene blue colour, indicating that H₂S in NaOH solution was readity: oxidized to other S forms which did not undergo methylene blue development.

Toluene and dioxane were compared as liquid scintillants for assaying ³⁵S activity trapped as H₂S in either NaOH or Zn‐Na acetate solution before and after methylene blue development. Before colour development, toluene improved the counting efficiency of ³⁵S in NaOH solution by 23 to 27%. After colour development, toluene improved the counting efficiency of both NaOH and Zn‐Na acetate solutions.     

A method for total phosphorus determinations in nitric‐perchloric digests of pine needles and roots

Abstract

A 2:1 nitric/perchloric acid plant digest was developed and tested as a replacement of the standard Kjeldahl digest for determining phosphorus concentrations in Pinus ponderosa Laws. needles and roots. Time sequence studies using the National Institute of Standards and Technology (NIST) pine standard reference material (SRM #1575) showed increased recovery of phosphorus as digest time increased from 1.5 to 16 hours. Digest intervals greater than 16 hours did not increase phosphorus recovery; the phosphorus concentration leveled off within the NIST reference material certified range. Using P ponderosa needle and root samples, a linear regression comparison determined that two sets of nitric/perchloric digests yielded 3.4% higher phosphorus concentrations than the Kjeldahl digest. However, 99 sets of nitric/perchloric digests, each containing two NIST standard reference materials (SRM), yielded an approximately normal distribution of phosphorus concentrations, all agreeing with the Kjeldahl established concentration and within the NIST SRM certified range. The 3.4% difference in phosphorus concentrations was consistant with the observed variability among sets. In conjunction with new elemental combustion methods for determining plant nitrogen, the nitric/perchloric digest can replace a Kjeldahl digest for determining plant phosphorus while determining additional plant cations not available using a Kjeldahl digest method.     

A simple manual method for the determination of phosphate‐extractable (ion‐exchange membrane) sulphate in soils

Abstract

A simple manual method for measuring phosphate‐extractable sulphate in soils using basic laboratory equipment is described. Sulphate is extracted by a phosphated anion‐exchange membrane which, after elution, is measured turbidimetrically as barium sulphate. The results obtained by the proposed manual method compare well with a continuous flow analyser method using a range of Pacific Island soils.     

A turbidimetric method for determining phosphate‐extractable sulfates in tropical soils

Abstract

Turbidimetric methods, using Ba ions to precipitate SO₄, are frequently used to determine soil sulfates extracted with phosphate solutions. These methods, as routinely performed, seriously underestimate SO₄ in some soils of the tropics because phosphate is removed from the extractant by soil adsorption and because many extracts fail to yield satisfactory precipitate even if the extracting procedure is adequate. Decolorizing the extracts with carbon black, treating extracts with strong oxidizing agents, adding SO₄ spikes, and seeding the extracts with BaCl₂ seed‐crystals improve precision, but some extracts, especially those from soils derived from volcanic ash, do not yield reliable precipitates even though these procedures are employed. This paper presents a method that consistanlty yielded more SO₄ than other turbidimetric procedures with which it was compared. The proposed method was further validated against an ion‐chromatographic method for SO₄ determination. The two methods yielded virtually identical results.

The proposed method consists of extracting SO₄ with 0.04 M Ca(H₂PO₄)₂ pH 4, at a soil‐to‐solution ratio of 1: 10. Repeated extraction is necessary for phosphate‐retentive soils. (A. single extraction was approximately 40% effective for removing indigenous SO₄ from a Hydric Dystrandept subsoil, approximately 78% effective for an Eutrustox.) Organic materials are removed from the extracts by adsorption on charcoal; SO₄ is concentrated in the extract by volume reduction; a SO₄ spike is added; BaCl₂‐seed crystal is added, after which volume is increased by adding BaCl₂ solution. Optical density is read at 600 nm.     

A graphical method for fertilizer sharing in a limited‐capital situation

Abstract

When fertilization capital is limited, the maximum economic rate which gives the greatest profit per unit area cannot be applied to all crops, therefore, a predicting method for the most profitable fertilizer rates for each crop is needed. This work describes a graphical method for sharing the available fertilizer between two different crops, or else the same crop in two different soils or crop sequences where the fertilizer needs are not the same. The method can also be used in the case of irrigation when the capital or the amount of the available water are limited.     

Simple method for 14C‐labelling root material for use in root decomposition studies

Abstract

A method was devised in which plant roots can be easily and uniformly radiolabelled with ¹⁴C for use in soil decomposition studies. The roots were labelled from an exogenous sugar solution for a total period of 48 hours after which root decomposition studies could be performed. The method offers distinct advantages over the existing constant ¹⁴C‐CO₂ atmosphere labelling method.