Yuanda Zhu

Use of portable X-ray fluorescence spectrometry for environmental quality assessment of peri-urban agriculture

Urban expansion into traditional agricultural lands has augmented the potential for heavy metal contamination of soils. This study examined the utility of field portable X-ray fluorescence (PXRF) spectrometry for evaluating the environmental quality of sugarcane fields near two industrial complexes in Louisiana, USA. Results indicated that PXRF provided quality results of heavy metal levels comparable to traditional laboratory analysis. When coupled with global positioning system technology, the use of PXRF allows for on-site interpolation of heavy metal levels in a matter of minutes. Field portable XRF was shown to be an effective tool for rapid assessment of heavy metals in soils of peri-urban agricultural areas.

Spatial Variability of Soil Properties at Capulin Volcano, New Mexico, USA: Implications for Sampling Strategy

Abstract Non-agricultural lands are surveyed sparsely in general. Meanwhile, soils in these areas usually exhibit strong spatial variability which requires more samples for producing acceptable estimates. Capulin Volcano National Monument, as a typical sparsely-surveyed area, was chosen to assess spatial variability of a variety of soil properties, and furthermore, to investigate its implications for sampling design. One hundred and forty one composited soil samples were collected across the Monument and the surrounding areas. Soil properties including pH, organic matter content, extractable elements such as calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), phosphorus (P), sulfur (S), zinc (Zn), and copper (Cu), as well as sand, silt, and clay percentages were analyzed for each sample. Semivariograms of all properties were constructed, standardized, and compared to estimate the spatial variability of the soil properties in the area. Based on the similarity among standardized semivariograms, we found that the semivariograms could be generalized for physical and chemical properties, respectively. The generalized semivariogram for physical properties had a much greater sill value (2.635) and effective range (7 500 m) than that for chemical properties. Optimal sampling density (OSD), which is derived from the generalized semivariogram and defines the relationship between sampling density and expected error percentage, was proposed to represent, interpret, and compare soil spatial variability and to provide guidance for sample scheme design. OSDs showed that chemical properties exhibit a stronger local spatial variability than soil texture parameters, implying more samples or analysis are required to achieve a similar level of precision.

Evaluation of Portable X-ray Fluorescence for Gypsum Quantification in Soils

The use of field portable X-ray fluorescence (XRF) spectrometry as a quantification tool for gypsum content in soils of West Texas and southern New Mexico, USA, was evaluated. Six sites were evaluated with gypsum contents ranging from less than 10% to greater than 90%. Samples collected from each site were scanned in the field using XRF and then transported to the laboratory for additional XRF scanning. Variables that might affect XRF scanning results, such as scanning time, particle size, moisture content, and so on, were evaluated. Both gypsum (CaSO4 • 2H2O) and calcite (CaCO3) were quantified using standard laboratory techniques. Three data sets were compared: (1) soil characterization data, obtained from the National Soil Survey Laboratory Research Database in Lincoln, NE; (2) quantitative X-ray diffraction; and (3) portable XRF (PXRF). The best correlation of gypsum XRF data (via Ca quantification minus calcite content) and laboratory data was between PXRF and quantitative X-ray diffraction (R = 0.96). On average, PXRF provided results within 6% of soil characterization data, the current laboratory standard for gypsum quantification. Field PXRF shows considerable promise as a rapid, quantifiable measure of gypsum in soils.

Determination of soil calcium using field portable X-ray fluorescence.

Soil calcium (Ca) determines several characteristics of soil fertility and affects many plant functions after absorption. It is necessary to develop a method to quickly determine soil Ca content in situ because soil Ca content can vary considerably in natural environments. Laboratory determination of Ca is laborious and costly. This study assessed the potential of field portable X-ray fluorescence (FPXRF) to be used in soil Ca determination. The consistency, repeatability, and accuracy of FPXRF are carefully examined using both artificial and natural soil samples. The effects of sample treatments including drying, bagging, grinding, and sieving on FPXRF are also investigated. Results show that FPXRF can detect and quantify total soil Ca content rapidly, accurately, and consistently with standard or specific calibration.

Soil Salinity Measurement Via Portable X-ray Fluorescence Spectrometry

Abstract Saline soils are defined as those containing appreciable salts more soluble than gypsum (e.g., various combinations of Na+, Mg2+, Ca2+, K+, Cl−, SO42-, HCO3−, and CO32-). Saline soils can occur across diverse climates and geological settings. As such, salinity is not germane to specific soil textures or parent materials. Traditional methods of measuring soil salinity (e.g., electrical conductance), although accurate, provide limited data and require laboratory analysis. Given the success of previous studies using portable X-ray fluorescence (PXRF) as a tool for measuring soil characteristics, this study evaluated its applicability for soil salinity determination. Portable X-ray fluorescence offers accurate quantifiable data that can be produced rapidly, in situ, and with minimal sample preparation. For this study, 122 surface soil samples (0–15 cm) were collected from salt-impacted soils of coastal Louisiana. Soil samples were subjected to standard soil characterization, including particle size analysis, loss-on-ignition organic matter, electrical conductivity (EC), and elemental quantification via PXRF. Simple and multiple linear regression models were developed to correlate elemental concentrations and auxiliary input parameters (simple: Cl; multiple: Cl, S, K, Ca, sand, clay, and organic matter) to EC results. In doing so, logarithmic transformation was used to normalize the variables to obtain a normal distribution for the error term (residual, ei). Although both models resulted in similar acceptable r2 between soil EC and elemental data produced by PXRF (0.83 and 0.90, respectively), multiple linear regression is recommended. In summary, PXRF has the ability to predict soil EC with reasonable accuracy from elemental data.

Influence of Ice on Soil Elemental Characterization via Portable X-Ray Fluorescence Spectrometry

Field portable X-ray fluorescence (PXRF) spectrometry has become an increasingly popular technique for in-situ elemental characterization of soils. The technique is fast, portable, and accurate, requiring minimal sample preparation and no consumables. However, soil moisture > 20% has been known to cause fluorescence denudation and error in elemental reporting and few studies have evaluated the presence of soil moisture in solid form as ice. Gelisols (USDA Soil Taxonomy), permafrost-affected soils, cover a large amount of the land surface in the northern and southern hemispheres. Thus, the applicability of PXRF in those areas requires further investigation. PXRF was used to scan the elemental composition (Ba, Ca, Cr, Fe, K, Mn, Pb, Rb, Sr, Ti, Zn, and Zr) of 13 pedons in central and northern Alaska, USA. Four types of scans were completed: 1) in-situ frozen soil, 2) re-frozen soil in the laboratory, 3) melted soil/water mixture in the laboratory, and 4) moisture-corrected soil. All were then compared to oven dry soil scans. Results showed that the majority of PXRF readings from in-situ, re-frozen, and melted samples were significantly underestimated, compared to the readings on oven dry samples, owing to the interference expected by moisture. However, when the moisture contents were divided into > 40% and < 40% groups, the PXRF readings under different scanning conditions performed better in the group with < 40% moisture contents. Most elements of the scans on the melted samples with < 40% moisture contents acceptably compared to those of the dry samples, with R 2 values ranging from 0.446 (Mn) to 0.930 (Sr). However, underestimation of the melted samples was still quite apparent. Moisture-corrected sample PXRF readings provided the best correlation to those of the dry, ground samples as indicated by higher R2 values, lower root mean square errors (RMSEs), and slopes closer to 1 in linear regression equations. However, the in-situ (frozen) sample scans did not differ appreciably from the melted sample scans in their correlations to dry sample scans in terms of R 2 values (0.81 vs. 0.88), RMSEs (1.06 vs. 0.85), and slopes (0.88 vs. 0.92). Notably, all of those relationships improved for

Soil Organic Carbon Variability in Croplands: Implications for Sampling Design

The variation of soil organic carbon (SOC) concentration is important not only for indicating the uncertainty of SOC stock at spatial scales, but also for calculating the minimum sample size to detect SOC concentration change temporally. The coefficient of variation (CV), an index often used to express the variation of SOC concentration, is affected by multiple sampling factors. Yet, minimization of the SOC concentration CV remains elusive. A total of 117 observations of the CV for SOC concentration in croplands were collected from 41 published studies. Pearson correlation analysis was used to determine the effect of three sampling factors, that is, sample size, sampling area, and sampling interval, on SOC concentration variation. Results showed that the SOC concentration of croplands was mostly low (CV, <15%) to moderately (CV, 15%-35%) variable. Significant linear relationships existed between the CV and sample size, and between the CV and log (sampling area), suggesting that stratified sampling may reduce SOC variation. A significant linear relationship also existed between the CV and log (sampling interval), indicating that soil spatial variability contributed to the high CV of SOC concentration. A maximum of 2 km of sampling interval was recommended for SOC stock investigations in croplands. These findings provide some guidance for optimum sampling design on SOC dynamics research.

Rapid Analysis of Elemental Concentrations in Compost Via Portable X-ray Fluorescence Spectrometry

The importance of compost testing for heavy metals and plant essential nutrients is vital to preventing the transport of toxic elemental loads and imperative to successful marketing of composted products. As such, a method to more efficiently test the elemental composition of compost would aid producers and compost analysis labs in evaluating and certifying the material prior to use. The use of portable X-ray fluorescence (PXRF) spectrometry for elemental compost analysis was investigated, to build on previous research, analyze technological improvements, test applicability of the technology on a wide range of compost types, and quantify the influence of moisture, particle size, organic matter and interelemental interactions on scan results. Several elements, specifically Ca, Cr, Cu, Fe, K, Mn, P, and Zn showed the most potential for analysis via PXRF in dried samples. Arsenic detection was found to be limited by the influence of Pb levels in the samples. Great potential for widespread evaluation and some definitive quantification of elemental concentrations via PXRF is recommended by this study.

Characterization of placic horizons in ironstone soils of Louisiana, USA.

Placic horizons, defined as thin, wavy, hardened layers of iron and organic matter, are rare within the United States, occurring only in Washington, Alaska, and Hawaii. While ironstone is common in many soils of the southeastern United States, it is not known to contain appreciable organic matter. As a pilot study evaluating the justification for a larger study on ironstone in Louisiana, a 40 m lateral exposure with suspected placic horizons was evaluated in Vernon Parish, Louisiana. Results of laboratory analysis show elevated levels of iron and organic matter in the suspect horizons that meet the criteria of placic horizons as defined by the Soil Survey Staff. Based on the results of this study, additional evaluation of multiple pedons with similar features is warranted. Should additional pedons demonstrate similar properties, a new great group of ‘Petrudepts’ would be needed to describe both the placic horizons in the pedon and the udic moisture regime in which they occur.

Soil series and land use impacts on major soil properties: a quantitative comparison

Human-induced soil change is attracting increasing attention, yet how to quantitatively measure anthropogenic impact on changes in soil properties remains unclear. Eight selected soil properties—bulk density (BD), sand, silt, and clay content, pH, soil organic matter (SOM), total carbon (TC), and total nitrogen (TN)—at four soil depths (0–10, 10–20, 20–30, and 30–40 cm) were measured across three soil series (Gallion, Latanier and Sharkey) in south-central Louisiana, USA, to quantify changes in soil properties as a function of three contrasting land use types, i.e. forest, cropland, and Wetlands Reserve Program. Partial eta-squared values (η2) derived from two-way analysis of variance were used to quantitatively compare natural factors (soil series) and anthropogenic impact (land use) on these soil properties. Results showed that properties such as BD, pH, SOM, TC, and TN could be easily changed by anthropogenic disturbance, especially at 0–10 cm, while soil texture was mainly a natural factor. The anthropogenic factor accounted for 55.2%, 39.5%, 33.2%, and 36.0% of changes in the soil properties at 0–10, 10–20, 20–30, and 30–40 cm depth, respectively. These findings highlight the anthropogenic impact on selected soil properties.