Elemental Analysis of Compost Using an Energy Dispersive X-Ray Fluorescence Spectrometer

Significance of the Topic

Applying compost as a fertilizer supports circular resource use and reduces greenhouse gas emissions from livestock waste and the demand for synthetic fertilizers. Reliable elemental analysis of compost is essential to optimize fertilization, safeguard food quality and the environment, and ensure safe use of regional organic resources. Rapid, accurate compositional methods that minimize sample pretreatment accelerate R&D, quality control and incoming inspection of compost-containing fertilizers.

Objectives and Study Overview

This study evaluated an ALTRACE energy dispersive X-ray fluorescence (EDXRF) spectrometer for qualitative and quantitative elemental analysis of compost. Key goals were to (1) demonstrate that EDXRF can produce results consistent with conventional ICP-AES (with digestion), (2) document a simple sample preparation workflow without acid digestion, and (3) assess the strengths and limitations of bulk XRF quantification for compost matrices.

Sample and Sample Preparation

• Material: Air-dried compost composed primarily of cattle and pig manure with rice husk as auxiliary ingredient.
• Drying: Samples were oven-dried at 110 °C for 2 h to reduce moisture for vacuum measurement; measured moisture loss was 12.5%.
• Presentation: Dried sample placed into a sample cell sealed with 5 μm polypropylene film.
• Analytical basis: Organic fraction (C–O) treated as CH2O balance; inorganic elements expressed as oxides for reporting.

Methodology

EDXRF measurement irradiates the sample with X-rays and detects characteristic fluorescence to determine elemental composition across the irradiated bulk. Quantification used the fundamental parameter (FP) method, which is theory-based and does not require matrix-matched standards for initial results. The approach provides a bulk-average composition and readily measures poorly soluble inorganic constituents (e.g., silica, alumina). Results were compared against multi-laboratory ICP-AES data (round-robin) where ICP measurements involved both acid digestion and hydrochloric acid extraction methods.

Instrumentation Used

• Instrument: ALTRACE energy dispersive X-ray fluorescence spectrometer (Shimadzu).
• Detector: Silicon drift detector (SDD).
• X-ray tube: Rhodium (Rh) target.
• Atmosphere: Vacuum measurement.
• Measurement strategy: Multiple tube voltages and primary filters were applied to optimize detection across element groups (examples: 65 kV for Sr–Ba, 50 kV for Fe–Rb and Pb, 30 kV for Ti–Mn, 15 kV for Na–Sc and S/Cl–Sc).
• Integration: 100 s × 5 channels; dead time maintained below 15%.

Analysis Conditions (summary)

• Target element range: Na (Z=11) to U (Z=92).
• Quantification: FP-based oxide concentrations; organic fraction set as CH2O.
• Sample handling: Minimal—drying and placement in film-covered cell—no acid digestion required for EDXRF.

Main Results and Discussion

• Qualitative coverage: EDXRF detected a wide suite of inorganic elements across the Na–U range and treated light organics as CH2O for mass balance.
• Quantitative outcomes: Major oxide concentrations (examples from the study) included SiO2 (~14.6%), P2O5 (~8–9.6% depending on table/format), CaO (~6.8–7.8%), and significant Fe, Mn, Zn and Cu levels reported as oxides or elemental mg/kg values.
• Comparison with ICP-AES: When ICP-AES results were obtained after complete acid digestion, ALTRACE EDXRF concentrations agreed well for many components (e.g., P2O5, K2O, CaO, MgO, Fe, Mn, Zn, Cu), with ALTRACE reporting values within reported uncertainties of the ICP digestion-based averages from a 22-laboratory round-robin.
• Observed discrepancies: Larger differences were noted for SO3 and for some heavy elements when compared to ICP-AES values obtained by hydrochloric acid extraction. These discrepancies are consistent with EDXRF measuring bulk (total) element content while extraction methods can have incomplete recoveries for poorly soluble or tightly bound species. A single data point for SO3 in this study also limits confidence for that analyte.
• Sources of analytical uncertainty: matrix effects, sample heterogeneity, oxide-conversion assumptions, limited calibration for matrix-specific sensitivity, and differences between total (XRF) vs. extractable (extraction-based ICP) fractions.
• Improvement potential: Applying empirical calibration using certified reference materials or matrix-matched standards to refine instrument sensitivity coefficients is expected to reduce systematic bias and improve absolute accuracy.

Benefits and Practical Applications

• Minimal pretreatment: EDXRF requires only drying and simple sample mounting—no acid digestion—reducing analysis time, reagent use, and chemical waste.
• Bulk analysis: The method measures average composition over the irradiated volume, which is advantageous for heterogeneous compost matrices and incoming raw material inspections.
• Capability for poorly soluble phases: EDXRF can quantify refractory inorganic components (e.g., silica and alumina) that may be under-represented by extraction procedures.
• Operational advantages: Faster sample throughput and simpler workflows support fertilizer R&D, process control, and rapid screening during raw material acceptance.

Future Trends and Potential Applications

• Calibration refinement: Development and adoption of compost-specific certified reference materials and empirical multi-point calibrations will improve quantitative accuracy of EDXRF for routine use.
• Hybrid workflows: Combining EDXRF for rapid bulk screening with selective ICP-based speciation for regulatory or extractable-fraction requirements will optimize cost and information content.
• Field/portable systems: Portable EDXRF instruments could enable on-site incoming inspection or rapid field surveys of compost quality, with appropriate validation against laboratory benchmarks.
• Automation and data integration: Automated sample handling, standardized protocols and integration with laboratory information systems will streamline QA/QC in fertilizer production and supply chains.
• Expanded parameter sets: Integration of elemental data with complementary measurements (C/N, pH, EC, organic matter characterization) will support more complete agronomic decision-making and environmental assessments.

Conclusion

This application demonstrates that modern EDXRF (ALTRACE) can deliver rapid, bulk elemental analysis of compost with quantitative results that compare favorably to ICP-AES values obtained after complete acid digestion. The method's minimal sample preparation, ability to measure poorly soluble inorganic constituents, and fast throughput make it a practical tool for fertilizer research, incoming raw-material inspection and routine screening. Accuracy for certain analytes and heavy elements can be further improved by instrument calibration with appropriate standards and by understanding differences between total versus extractable element fractions.

References

• Shimadzu Corporation (2026). Elemental Analysis of Compost Using an Energy Dispersive X-Ray Fluorescence Spectrometer. Application News (ALTRACE EDXRF).
• Zenkoku Tsuchi no Kai. Round-robin test results for compost analysis (participants: 22 institutions), Japan. Used as the comparative ICP-AES dataset in the study.