A method for the determination of β-glucosidase activity in soil

A method is described for the rapid and simple assay of soil β-glucosidase activity. It involves colorimetric estimation of ρ-nitrophenol released by β-glucosidase activity when soil is incubated in McIlvaine buffer (pH 4.8) with ρnitrophenyl βd-glucoside and toluene at 30°C for 1 hr. The method has been applied to three different soils. The range of β-glucosidase activity in cultivated soils was from 10.1 to 15.2 mµ mole per min per gram of dried soil. K_m value for ρ-nitrophenyl β-d-glucoside was 3.3 × 10^-4 M. Optimum pH was 4.8.     

A simple method for determination of ammonium in semimicro‐Kjeldahl analysis of soils and plant materials using a block digester

Abstract

A simple method for determination of ammonium in semimicro‐Kjeldahl analysis of soils and plant materials using a Tecator or Technicon 40‐tube block digester is described. It involves use of an inexpensive steam distillation apparatus that permits direct distillation of ammonium from the tubes used for Kjeldahl digestion in 40‐tube block digesters. The method is rapid and precise, and it gives results that agree closely with those obtained by the customary method of ammonium N analysis involving transfer of the Kjeldahl digest before distillation.     

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.     

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.     

Depletion of plant‐available silicon in soils: A possible cause of declining rice yields

Abstract

The phenomenon of yield decline in different rice ecosystems from many parts of the world has been reported to be associated with decreases in the effective nitrogen (N) supply from soil. However, many reports in the literature suggest that silicon (Si) is an agronomically essential element for sustainable rice production. Depletion of plant‐available Si in soils where rice is grown could be a possible limiting factor contributing to declining yields. In order to address this problem of yield decline or stagnation, it seems necessary to survey Si status of soils and rice grown in different ecosystems throughout the world and develop region‐specific integrated nutrient management systems that include the element Si.     

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.     

A computer‐assisted method for CEC estimation and quality control in a routine soil‐test operation

Abstract

Cation‐exchange capacity (CEC) of 30 Alabama soils was estimated by two different methods based or routine soil‐test results consisting of soil‐water pH, Adams‐Evans buffer pH, and Mehlich‐1 extractable cations (K, Mg, and Ca), which were obtained automatically by a computerized data acquisition system. In one method, CEC was calculated by solving a quadratic equation involving soil‐water and buffer pH's; in the other, CEC was estimated as the summation of extractable cations and exchangeable acidity. The two estimated CEC's agreed well with each other and also had the same magnitude as CEC determined by the normal NaOAc, pH 8.2 method. By averaging the two calculated values, an even closer estimation of the measured CEC was found. These calculations and comparisons can be accomplished quickly and efficiently by a minicomputer via a simple FORTRAN program.

In addition, a discrepancy between the two estimated CEC's would indicate possible errors in analytical determinations and/or the inadequacy of the soil testing procedures. Therefore, an additional means for quality control in a routine soil‐test operation can be obtained by comparing the two CEC values.     

A simplified Shaw's wet‐combustion technique for determination of carbon in plant materials

Abstract

A simplified Shaw's wet‐combustion technique for carbon (C) determination in plant materials is described which requires less reagent and operation time. The simplified technique gave high recovery (99.4%) of the C in analytical pure grade sucrose and citric acid, and high reproducibility of C measured in 18 different plant materials.     

Manganese‐iron interactions in the plant‐soil system

Dicotyledonous plants had significantly higher Mn and Fe intake rates on a near neutral soil, had a significantly higher Mn intake rate on a slightly calcareous soil, but had lower Mn and Fe intake rates on a calcareous soil, than monocotyledonous plants. This dependency on soil reaction suggests that dicots utilize primarily a chemical reduction mechanism, whereas monocots utilize some less pH‐dependent mechanism (possibly Mn(III)‐, Fe(III)‐organic complexation) to mobilize soil Mn and Fe. Soluble soil Mn and Fe fractions in the rhizosphere were consistently positively correlated with each other, as were Mn and Fe intake rates. These results suggest that for soil‐grown plants, Mn and Fe uptake was positively interrelated because both Mn and Fe were mobilized by similar root processes.     

Evaluation of efficient soil test methods for Zn and their critical vales in salt‐affects soils for rice

Abstract

Soil pot culture experiment was conducted on 22 soils of Balewal‐Phaguwala‐Narike (BPN) and 24 soils of Isri‐Langrian‐Narike (ILN) associations using rice (PR 106) as test crop at 0 and 7.5 ppm Zn levels. Chelating extractants 0.005M DTPA, 0.01M EDTA‐(NH₄)₂CO₃ and 0.05M EDTA, extracted more soil Zn than double‐acid and were significantly correlated with each other as well as with soil pH and clay in BPN and only with clay in ILN soil association. Soil CaCO₃ governed the double‐acid extractable Zn in these soils. Dry matter yield and Zn uptake by rice significantly increased with 7.5 ppm Zn application. The response was higher in ILN than BPN soil association, The DTPA method gave the highest correlation with Bray's yield and Zn uptake (r =0.72 and 0.55) followed by 0.05M EDTA (r ‐ 0.75 and 0.61) or EDTA‐(NH₄)₂CO₃ (r =0.70 and 0.61). The predictability of rice yield improved from 18–27 to 27–35, 32–43, 34–44 and 51–55 percent as a result of stepwise inclusion of pH, CaCO₃, organic carbon (OC) and clay respectively in the regression equation alongwith Zn extracted by chelating agents.

The critical levels of DTPA, EDTA‐(NH₄)₂CO₃ and EDTA extractable Zn significantly differed in the two associations and were 0.69, 0.82 and 1.24 ppm in BPN and O.BC, 1.09 and 1.42 ppm in ILN soil association. Soil properties further affected the critical levels. This for DTPA available Zn was 0.80 and 1.03 ppm in soil containing less and greater than 2% CaCO₃, 1.03 and 0.80 ppm in soils containing less and greater than 0.25% OC. These values for EDTA‐(NH₄)₂CO₃ available Zn were 1.09 and 0.91 ppm Zn in soils containing less and greater than 15% clay suggesting that critical levels of Zn for each category of soil properties should be considered while making recommendations of Zn fertilization of crops.,     

A quick‐test procedure for soil and plant tissue nitrates using test strips and a hand‐held reflectometer

Abstract

Development of a nitrate quick‐test for use by fanners or field consultants would likely encourage the use of plant tissue and soil nitrate tests as a means to improve nitrogen management. To evaluate a quick‐test method, nitrate concentrations in plant tissue and soils were measured using commercially available nitrate test strips and a hand‐held reflectometer. The results were compared with those obtained with standard laboratory methods. Test strip accuracy and precision and reflectometer precision were determined over a 10 day period using standard KNO₃solutions and colored paper strips. Coefficients of variation ranged from 22.4 to 9.5 percent for the test strips and from 3.5 to 1.6 percent for the reflectometer. Quick‐test results were highly correlated with laboratory results for both plant tissue nitrate (r=0.87) and soil nitrate (r=0.98) concentrations. Results indicated that test strips provide a rapid, reasonably accurate and precise method to determine nitrate concentrations in both soil and plant material     

A quick test procedure for soil nitrate‐nitrogen

Abstract

A procedure for extraction and measurement of nitrate‐nitrogen (NO₃‐N) in soil is described. Extracting solution [0.025M Al₂(SO₄)₃] and field‐moist soil are measured volumetrically, with NO₃‐N concentration measured by nitrate‐sensitive colorometric test strips or nitrate‐selective electrode. Across a range of soil texture, moisture content, and NO₃‐N concentration, the procedure was well correlated with conventional laboratory analysis of 2N KC1 soil extracts (r² = 0.94). This quick test procedure is proposed as an on‐farm monitoring technique to improve N management.     

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.     

Can sieving size affect the determination of soil available micronutrients?

<正>Dear Editor,Globally, approximately two billion people suffer from micronutrient deficiencies(Tulchinsky, 2010; Myers et al.,2014).Soil micronutrient availability is of great importance for the evaluation of soil fertility and the determination of appropriate measures for improving crop quality and human health.The diethylenetriamine-penta-acetic(DTPA)     

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.     

Application of the Berthelot reaction to the determination of ammonium‐N in soil extracts and soil digests

Abstract

The phenol‐hypochlorite‐ammonium reaction of Berthelot can be utilized in manual procedures for the analysis of NH₄‐N in a variety of soils applications, including total N measurement in soils, particle size separates and soluble organic matter fractions, and in measuring NH₄‐N in soil extracts. A simple, convenient, and versatile procedure is described.     

Mobile Si-rich compounds in the soil–plant system and methods for their determination

Different aspects of Si biogeochemistry in the soil have been reviewed. Interaction mechanisms of monosilicic acid with aluminum, phosphorus, and heavy metal compounds have been generalized. Polysilicic acids are chemically inert substances, but they participate in the formation of soil structure. Organosilicon compounds in the soil are very little investigated. From literature and our own data, the cycle of mobile Si forms in the soil–microorganism–plant system has been suggested, which shows the main fluxes of soluble Si migration and transformation. A new classification of the Si compounds based on their physicochemical and biological activities in the soil has been suggested as well as a method for the determination of mono- and polysilicic acids in the soil matrix.     

A phenol‐hypochlorite manual determination of ammonium‐nitrogen in Kjeldahl digests of plant tissue

Abstract

A phenol‐hypochlorite (Berthelot) procedure for determining NH₄‐N in acid digests of plant tissue is described. EDTA suppresses Cu interference and precipitation of hydroxides and phosphates. The oxidizing reagent includes an alkaline buffer to account for variations in acidity between digestion solutions, the main source of error in an unbuffered procedure. The reagent combinations and addition sequence employed allow for delays of up to at least 30 minutes between reagent additions without affecting the final colour intensity. The proposed procedure is as sensitive as similar methods used for determining NH₄‐N in natural waters and yields results which agree well with those obtained by steam distillation.     

Colorimetric determination of phosphorus in citrate‐bicarbonate‐dithionite extracts of soils

Abstract

Existing colorimetric methods for determining phosphorus (P) in citrate‐bicarbonate‐dithionite (CBD) extracts from soils and sediments require pretreatments of extracts prior to the determination of the element. A method is proposed for the determination of P in CBD extracts without any chemical treatments. Maintaining the citrate concentration below 2.4 mM, maximum and stable absorbance develops in P‐Mo‐Sb system within one hour and remains stable for 20 hours. An evaluation of potential interference was made by adding varying amounts of P to CBD extracts over a range of extractable iron (Fe) and aluminum (Al) levels. Near 100 percent recovery of the added P suggests the applicability of the method to soils and sediments. Major advantages of the method are speed, simplicity, reliability and stability of the colored complex.     

A method for estimating organic‐bound iron and aluminum contents in soils

Abstract

Estimation of organic‐bound iron (Fe) and aluminum (Al) is an important diagnostic technique in pedology. The commonly used sodium pyro‐phosphate method yields somewhat ambiguous results and is inconvenient if an ultracentrifuge is not available in the laboratory. This study showed that 0.1M sodium nitrilotriacetate (NTA) could be used instead of pyrophosphate. The Fe and Al extracted by 0.1 M NTA were highly correlated to that by sodium pyrophosphate with R² = 0.993 for Fe and R² = 0.992 for Al, while the dissolution effects on standard mineral samples in NTA was kept at a minimum. NTA has the advantage of not requiring ultrafiltration, ultracentrifugation, or the addition of a flocculating agent as is the case for the pyrophosphate method.