Evaluating the impacts of incubation procedures on estimated Q10 values of soil respiration

A reliable determination of the response of soil organic carbon decomposition to temperature is critical in the context of global warming. However, uncertainties remain in estimated temperature sensitivity of soil respiration, which may be partly due to different experimental conditions. To investigate the possible effects of laboratory incubation procedures on estimated Q₁₀ value, soil samples taken from various ecosystems were incubated under changing temperature with different experimental conditions or procedures: 1) different rate of temperature change; 2) different intervals of temperature change; 3) equilibration time after temperature change; 4) the duration of chamber closure and 5) the size of incubated soil sample. The results indicated that respiration rate was affected by experimental procedures. The respiration rate of soil samples containing high concentration of organic carbon decreased quickly if the soil container sealed longer than 2 h. Estimated Q₁₀ values across all soils ranged from 1.56 to 2.70, with respect to the effects of incubation procedures. Temperature rate change, equilibration time, the duration of chamber closure and soil sample size had no effect on estimated Q₁₀ values of soil respiration. However, Q₁₀ values derived from temperature changing intervals of 2 and 7 °C were significantly different, despite the fact that the exponential function fitted well for the relationship between respiration rate and temperature for both intervals. The results of these experiments suggested that incubation procedures have different effects on measured soil respiration and estimated Q₁₀ values. For soil incubations of short-duration, the effects of incubation procedures on soil respiration and estimated Q₁₀ values based on respiration rate should be appropriately tested with experimental setting-up, and estimating Q₁₀ values with few temperatures should be avoided.     

A rapid method for the determination of fixed ammonium in soil

Abstract

Five different procedures for the oxidation of organic carbon were compared in order to determine the most suitable method for use as a pretreatment before the determination of fixed NH₄‐N in soils. Three of the procedures involved a method based on the use of a solution containing 0.1M Na₄P₂O₇, 0.1M NaCl, and 6% H₂O₂, applied for three different periods of time, 10 days, 20 days, and whatever number of days are required until frothing no longer occurs. This third period of time is designated as NF (no frothing). The remaining two procedures involved a method based on the use of a 3M NaOCl solution applied for two different periods of time, 3‐cycles and 5‐cycles.

Two of the procedures, the NF treatment with H₂O₂+NaCl+Na₄P₂O₇ and the 5‐cycle treatment with NaOCl, were found to give the must efficient removal of organic C. The amount of residual N in the soil after the NF treatment was highly correlated with the amount of residual N in the soil after the 5‐cycle treatment. It is concluded that the 5‐cycle treatment is as effective as the NF treatment for the oxidation of organic C in the soil before carrying out the determination of fixed NH₄‐N. The 5‐cycle treatment has the advantage of being a faster and simpler analytical procedure than the NF treatment.     

The variability between different analytical procedures and laboratories for measuring soil microbial biomass C and biomass N by the fumigation extraction method

The interlaboratory variations in the fumigation extraction method and the analytical procedures for measuring C and N in the soil microbial biomass were tested with one soil sample, and two soil extracts (non-fumigated and fumigated) sent to 25 different laboratories. Four groups of analytical procedures for organic C, i.e. (1) oven oxidation/ IR detection, (2) UV-persulfate oxidation/lR detection, (3) UV-persulfate oxidation/colorimetric detection and (4) dichromate oxidation/ titration, and three groups for total N, i.e. (1) Kjedahl reduction to NH₄⁺, (2) UV-persulfate and (3) persulfate-borate oxidation to NO₃^? were used by the different laboratories. The coefficient of variation for C and N measurements between different laboratories and analytical procedures varied between 15 and 34% in non-fumigated samples, between 13 and 20% in fumigated samples, and between 12 and 24% in the differences E_c and E_N. The average coefficients of variation between the replicate measurements within one laboratory were much smaller, i.e. they varied between 3.0 and 9.2% in non-fumigated samples, between 2.4 and 5.5% in fumigated samples, and between 4.5 and 12.8% in the differences E_c and E_n. Extraction and fumigation were not the major source of the variations observed. They were mainly a result of differences in the analytical procedures used to measure the low concentrations of C and N in the extracts. However, all of these analytical procedures should be able to measure correct values if they are properly calibrated and performed.     

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

Abstract

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

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.     

Water Quality Modeling of the Kali River,India

Water quality monitoring procedures effective in calibrating the QUAL2E model for the Kali River in India are described. The stability of dry season conditions for the Kali River are utilized to consider the migration pathways, and hence the calibration efforts necessary for water quality models. Alternative procedures for calibrating values for the reaction rates are utilized for reinforcement of the findings. These alternatives include changes in stream turbidity which are shown to be a useful measure of benthic oxygen demand. Ratios of BOD₅ to COD are reported between sugar mills, industrial inputs and municipal sources.     

Comparison of five methods to determine the cation exchange capacity of soil

Background

Cation exchange capacity (CEC) is a routinely measured soil fertility indicator. The standard NH₄OAc (pH 7) extraction procedure is time-consuming and overestimates actual CEC values of variable charge soils. Unbuffered extractants have been developed to measure the effective CEC (eCEC), but they differ in the type of index cation and extraction procedures.

Aim

This study was set up to systematically compare CEC values and exchangeable cation concentrations among different procedures and evaluate their practical aspects.

Methods

Five procedures were compared for (e)CEC, that is, silver thiourea (AgTU), cobalt(III) hexamine (Cohex), compulsive exchange (CE, i.e., BaCl₂/MgSO₄), BaCl₂ (sum of cations in single-extract), and NH₄OAc (pH 7). We applied these methods to a set of 25 samples of clay minerals, peat, or samples from soils with contrasting properties.

Results

The CEC values correlated well among methods (R² = 0.92–0.98). Median ratios of eCEC (AgTU as well as CE) to the corresponding eCEC (Cohex) value were 1.0, showing good agreement between eCEC methods, but NH₄OAc exceeded Cohex values (ratios up to 2.5 in acid soil). For BaCl₂-extracteable cations, the ratio ranged from low (<1.0) in acid soils (acid cations not measured) to high (>1.0) in high-pH soil (dissolution of carbonates). Multiple-extraction methods (CE and NH₄OAc) yielded more variation and increased labor.

Conclusions

The chemical properties of the sample cause method-specific interactions with chemical components of extractants. We found the Cohex method with ICP-MS detection to be the most efficient and cost-effective technique for determination of eCEC and exchangeable cations.     

Microwave digestion of fertilizers and soil amendments

Abstract

The trace element pollution hazard of the continuous and large scale application of fertilizers and other amendments to soils depends in part on the chemical composition of these materials. Complete sample dissolution is generally required prior to total elemental analyses. The objectives of this study were to evaluate closed vessel microwave digestion procedures, using HNO₃, HF, H₂O₂, and H₃BO₃, for the total dissolution of fertilizers and soil amendments and to develop a general digestion guide for individual samples. Twenty‐six materials, including commercial fertilizers, rock phosphate, liming materials, organic sources, and a soil sample were studied. More than 99.5% of each of these materials could be dissolved. Commercial nitrogen (N) fertilizers, most of the ammonium phosphates, and a potassium chloride sample could be completely dissolved using exclusively HNO₃. The other samples required HNO₃ and HF, used either in mixtures or consecutively in a stepwise procedure. The sewage sludge materials, the soil sample, and one of the rock phosphates were the only samples that could not be totally dissolved. No improvement in the digestions was observed by including H₂O₂. No significant contamination was evident during the digestions and satisfactory recoveries of 14 trace elements were obtained in digests of 2 standard reference materials. The proposed dissolution procedures are simple and safe. The usual quickness of microwave procedures was partially sacrificed to obtain a more complete dissolution of the samples. Digests obtained with these procedures could be potentially analyzed for other analytes, with the obvious exceptions of N, fluorine (F), and boron (B).     

Cation exchange capacity measurements

Abstract

Soil cation exchange capacity (CEC) measurements are important criteria for soil fertility management, vaste disposal on soils, and soil taxonomy. The objective of this research was to compare CEC values for arable Ultisols from the humid region of the United States as determined by procedures varying widely in their chemical conditions during measurement. Exchangeable cation quantities determined in the course of two of the CEC procedures were also evaluated. The six procedures evaluated were: (1) summation of N NH₄OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus BaCl₂ ‐ TEA (pH 8.0) exchangeable acidity; (2) N Ca(OAc)₂ (pH 7.0) saturation with Mg(OAc)₂ (pH 7.0) displacement of Ca²⁺; (3) N NH₄OAc (pH 7.0) saturation with NaCl displacement of NH₄ ⁺; (4) N MgCl₂ saturation with N KCl displacement of Mg²⁺; (5) compulsive exchange of Mg²⁺ for Ba²⁺; and (6) summation of N NH₄OAc (pH 7.0) exchangeable Ca, Mg, K, and Na plus N KCl exchangeable AJ. The unbuffered procedures reflect the pH dependent CEC component to a greater degree than the buffered methods. The compulsive exchange and the summation of N NH₄OAc exchangeable cations plus N KCl exchangeable Al procedures gave CEC estimates of the same magnitude that reflect differences in soil pH and texture. The buffered procedures, particularly the summation of N NH₄OAc exchangeable cations plus BaCl₂ ‐ TEA (pH 8.0) exchangeable acidity, indicated inflated CEC values for these acid Ultisols that are seldom limed above pH 6.5. Exchangeable soil Ca and Mg levels determined from extraction with 0.1 M BaCl₂ were consistently greater than values for the N NH₄Oac (pH 7.0) extractions. The Ba²⁺ ion is apparently a more efficient displacing agent than the NH₄ ⁺ ion. Also, the potential for dissolving unreacted limestone is greater for the Ba₂ ⁺ procedures than in the NH₄ ⁺ extraction.     

Quantifying the underestimation of soil denitrification potential as determined by the acetylene inhibition method

The acetylene inhibition technique (AIT) is commonly used for the determination of soil denitrification potential (SDP). However, the results obtained with this technique have intrinsic uncertainties. This study aimed at quantifying these uncertainties. A silt loam topsoil from an experimental station was incubated under standard conditions for SDP measurements, with and without acetylene additions. Changes in the concentrations of N₂O and N₂ in the headspace of incubation vials were monitored during the incubation, using a robotized sampling and analyzing system. Our results showed that the AIT did not completely inhibit the reduction of N₂O to N₂. As much as 11.7% of the produced N₂O was reduced into N₂ in the presence of acetylene. We conclude that SDP has to be corrected when determined by the AIT. The procedures used in this study will allow the estimation of correction factors, possibly as function of soil type and environmental conditions.     

Inorganic N analysis of soil extracts by automated and distillation procedures

Abstract

A comparison was made of automated procedures and steam distillation for analysis of NH₄ ⁺ and NO₃ ^‐ in KCl extracts of soils. Automated analysis of NH₄ ⁺ utilized the phenate‐hypochlorite reaction. Nitrate was analyzed by E. coli reduction of NO₃ ^‐ to NO₂‐which was then determined colorimetrically by reaction with sulfanilamide and napthylethylenediamine diHCl. Soil extracts were made with 1 M and 2 M KCl. Extracting with 1 M KCl was as effective as 2 M KCl. Extracts in 1 M KCl did not interfere with E. coli reduction of NO₃‐, but 2 M KCl did. The automated procedures when compared to distillation gave similar if not better precision and reduced variation particularly at low N concentrations. The automated procedure tended to give higher values at higher NO₃‐concentrations. Reduced time required for the analyses provided an additional advantage for the automated procedures.     

A comparison of methods for measuring extractable Ca,Mg, K,Na, Mn,Al, Fe,and P from New England forest soils

Abstract

An experiment was designed to evaluate several of the commonly used extractants and methods for determining “available”; elements in soils. The purpose of the study was to evaluate the suitability of these extraction procedures for use on forest soils typical for New England commercial forests. The extraction procedures selected included NH₄OAc pH 4.8, NH₄OAc pH 7.0, NH₄Cl, Double Acid, Bray, and Mehlich methods. The elements measured varied somewhat by procedure but included the base cations, Al, Fe, Mn, and P. As a bioassay of element availability, a greenhouse study was conducted using six forest soil materials from different horizon types (i.e. O, Ap, B) and three conifer seedling species (red spruce, balsam fir, and white pine). Relatively small differences among extraction procedures were found among the methods used for exchangeable Ca, Mg, K, and Na. Large differences, however, were found among the different horizon types in the amount of exchangeable base cations present. In contrast, significant differences were found among extraction procedures for Al, Fe, Mn, and P depending on the degree of buffering and acidity of the extracting solution. Of the elements measured in this study, only P appeared to be growth limiting with the NH₄OAc pH 4.8 being best correlated with P uptake by seedlings. Further work under field conditions over longer time periods is required to evaluate these methods for measuring P availability in forest soils     

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

Abstract

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

Size and shape of fine quartz in the clay fraction of soils and geological materials

Fine clay fractions of two soils and five geological materials including three formed in late Wisconsinan glacial rock flour were separated by decantation and centrifugation procedures. X-ray diffractograms (XRD) showed mica and chlorite as the main components. Pyrosulfate fusion which removed the phyllosilicates and iron oxides revealed presence of quartz and some feldspars. After dilute H₂SiF₆ treatment, blade-shaped, platy and sheroidal particles mainly of 0.2–0.1 μm size were observed by scanning electron microscope. Fine feldspars and quartz were found to be susceptible to the chemical treatments. On treatment with diluted H₂SiF₆ + HF + H₃BO₃, the crystallinity of fine quartz was considerably decreased as indicated by a very broad diffraction maximum at a spacing of about 4 Å.     

A bioassay to determine the effect of organic matter and pH on the effectiveness of nitrapyrin (N-Serve) as a nitrification inhibitor

The aerobic incubation procedures commonly used in biological studies have several disadvantages to assess inhibition of nitrification. Therefore, a more suitable procedure was developed. It involves pre-incubating soil samples treated with (NH₄)₂HPO₄ to establish a uniform population of nitrifiers before the addition of the nitrification inhibitor or other amendments. Through successive additions of (NH₄)₂HPO₄, a constant nitrification rate is maintained. This system enables direct comparison between treatments throughout the experiment.Data obtained using this procedure indicated that sorption of Nitrapyrin (NI) is a major factor decreasing the effectiveness of NI in organic soils. Loss of NI by volatilization also decreased its effectiveness, while the relative inhibition by NI was found to increase as soil pH increases. The greater susceptibility of nitrifiers to NI at high pH may be due to a relationship between pH and nitrifier ecology.     

The release of polonium-210 upon the recrystallization of Ba(Ra)SO4

An old sample of Ra-bearing BaSO₄ has been leached in H₂O and in aqueous KNO₃ to determine whether or not²¹⁰Po and²¹⁰Pb are released to the solution on recrystallization of the BaSO₄. Despite the expectation of release, no more than 0.03 % of the²¹⁰Po and 0.03 % of the²¹⁰Pb were released after periods of up to 30 days of vigorous stirring. The concentrations of²¹⁰Po and²¹⁰pb seem to reach a maximum after two or three days and not to rise further. Two new simplified procedures for²¹⁰Po determination are described briefly.     

Extractable Concentrations of Cobalt from Serpentine Soils with Several Single‐Extraction Procedures

In this study, we selected three soil pedons on the shoulder, backslope, and footslope along a serpentine toposequence to measure cobalt (Co) extractability using six single‐extraction procedures. These extraction procedures are distilled water, 0.11 M acetic acid in the first step of the BCR sequential extraction (BCR1), 1 M ammonium acetate (NH₄OAc; pH 7.0), 0.01 M calcium chloride (CaCl₂), diethylenetriamine pentaacetic acid (DTPA), and 0.1 M hydrochloric acid (HCl). Although the Co concentrations in the water extracts of the study soils ranged from 0.15 to 0.93 mg kg^?1, those with HCl extraction can be up to 22.1 mg kg^?1. The extractable Co concentrations in the study soils demonstrate that the extraction capacity is in the order HCl > DTPA > CaCl₂ ? NH₄OAc > BCR1 > H₂O. The percentages of extractable Co after applying the six single‐extraction procedures reveal that Co mobility is greatest in the soils on the backslope, moderate on the footslope, and least mobile on the shoulder.     

Rapid perchloric acid digest methods for analysis of major elements in plant tissue

Abstract

The nutrient element composition of tissue from a plant species is not fixed. Composition in the plant varies among different plant parts at the same or different physiological stages of maturity, as soil type changes, from day to day, even hour to hour on the same day due to past and current environmental conditions. These observations seem to undermine the general trend in plant tissue analysis to develop quantitative procedures that are time consuming and, therefore, foster insufficient nutrient status monitoring within and/or between different physiological stages of maturity of like or different plant parts. Therefore, until tissue sampling becomes more definitive, a digest procedure with 90–100% recovery should be more than adequate for major elemental analysis. The HClO₄ digestion procedures described here meet that requirement and take only 15 to 30 min to complete. N recovery was greater than 100% with the H₂O₂‐HClO₄ digestion procedure. However, when HNO₃ was combined with H₂O₂ and HClO₄, N was lost, although even then N volatilization occured only when digestion was extended past clearing.     

Standardisation of Methods for Long-Term Monitoring

A monitoring programme should be designed for duration. This means that methods should not only be appropriate with respect to detection limits and accuracy, but they should also be as simple as possible and they should be documented in such a way that measurements will be comparable over many decades. In this connection, it is particularly important to understand that results are dependent on methods, instruments and procedures. Within the European monitoring network (EMEP) there are several different sampling procedures for the main air components, SO₂, NO₂, SO₄ ^2?, NO₃ ^? + HNO₃, and co-located experiments have therefore been initiated to quantify the difference between the measurements. Reference methods and reference instruments corresponding to the recommendation in the EMEP Manual have been run together with the usual measurements at EMEP sites in several countries. The results are generally satisfactory, especially in the case where identical methods are used. However, there are also some unacceptable differences, e.g. when comparing NO₂ and SO₂ monitors with the reference methods. The monitors do have a main advantage of providing easily accessible data with short time resolution; nevertheless, the accuracy at low concentrations is usually poor. The traditional reference methods need development and simplification in the direction of the more appealing automatic instruments.     

Effectiveness of three rapid digestion methods to estimate total lead in orchard soils

Abstract

High concentrations of lead in contaminated soils comprise a potential public health hazard. Limits between safe and dangerous levels are often based on total soil lead content. Current chemical procedures to determine total lead are unsuitable for routine soil analysis because they are time‐consuming and require highly trained personnel. This paper describes the effectiveness of three rapid extraction procedures to estimate total lead in a large number of lead arsenate‐contaminated orchard soils. Dissolution of soil lead in Kjeldahl flasks using a nitric acid‐perchloric acid mixture was virtually complete (98%) when compared to values for total lead measured by treatment with a mixture of HF, HNO₃ and KClO₄. Shaking of 5‐g samples in 50 ml of lN HCl or lN HNO₃ for 1½ hours extracted 95 and 93 percent of the total lead, respectively. Regression equations were derived to allow estimation of total lead from values obtained in the HNO₃‐HClO₄, HCl, or HNO₃ extracts. The HNO₃‐HClO₄ digestion procedure is preferred with atomic absorption spectrophotometry, while HCl extraction is suitable for routine soil analysis with inductively coupled argon plasma spectrophotometers or similar instrumentation.

Grinding of the soils to promote sample uniformity appeared unnecessary, at least in the silt loam soils tested.