Soil composition analysis testing provides quantitative data on the physical, chemical, and biological constituents of soil, supporting decision-making in agriculture, environmental protection, and construction. Accredited third-party laboratories measure parameters such as pH, organic matter, nutrients, heavy metals, and organic pollutants in accordance with ISO, ASTM, EN, and GB standards. This technical guide explains the scope of soil analysis, common testing items, analytical methods, quality standards, and practical answers to frequently asked questions.
Technical Overview
Soil composition analysis testing is a systematic laboratory process used to identify and quantify the mineral, organic, liquid, and gaseous components of soil, together with its nutrient status and contaminant burden. Soil is a heterogeneous matrix composed of mineral particles (sand, silt, and clay), organic matter, soil solution, and soil air. The proportions of these fractions, along with the concentrations of chemical species within them, determine soil fertility, ecosystem health, geotechnical behavior, and environmental risk.
Modern soil testing follows a defined workflow that ensures data comparability and legal defensibility. Results are typically evaluated against risk screening values such as those in GB 15618-2018 for agricultural land and GB 36600-2018 for development land, as well as international benchmarks published by ISO and ASTM. Typical project drivers include fertilizer recommendation, contamination site investigation, land transfer and redevelopment, remediation verification, and regulatory compliance reporting.
- Sampling design and field collection according to a quality assurance plan
- Pretreatment: air-drying, grinding, sieving, and homogenization
- Extraction or digestion to bring target analytes into measurable form
- Instrumental analysis with calibrated methods and certified reference materials
- Data validation, quality control review, and issuance of an accredited test report
Testing Samples
Agricultural and Horticultural Soil
Farmland, orchard, vegetable base, greenhouse, nursery, and garden soils are analyzed to evaluate fertility, guide balanced fertilization, and diagnose nutrient deficiency or excess. Sampling is usually performed at plow depth (0–20 cm) with sub-samples combined into a representative composite sample.
Development Land and Construction Site Soil
Soil from residential, commercial, and industrial development plots is tested against risk screening values for inorganic and organic contaminants before excavation, backfill acceptance, or land-use change approval. Geotechnical and corrosivity parameters may be added for engineering design purposes.
Contaminated Site and Industrial Soil
Soil from former factories, fuel stations, mining areas, landfills, and storage yards is tested to delineate contamination plumes, classify waste, and verify that remediation targets have been achieved after treatment.
Sediment, Sludge, and Soil Amendments
River and lake sediment, sewage sludge intended for land application, compost, biochar, and other soil conditioners are analyzed for heavy metals, nutrients, and pathogens to confirm suitability and regulatory compliance.
Testing Items
Testing schemes are tailored to project objectives, applicable standards, and the suspected contaminant profile of the site. The most frequently requested parameter groups are summarized below.
Physical and Physicochemical Indicators
- Moisture content, dry bulk density, and particle density
- Particle size distribution (sand, silt, clay) and soil texture classification
- pH and electrical conductivity (EC)
- Organic matter and soil organic carbon
- Cation exchange capacity (CEC) and exchangeable bases (Ca, Mg, K, Na)
- Porosity and water-holding characteristics
Nutrient Indicators
- Total nitrogen, hydrolyzable (alkali-hydrolyzable) nitrogen
- Total phosphorus, available phosphorus (Olsen or Bray extractable)
- Total potassium, slowly released potassium, available potassium
- Secondary nutrients: calcium, magnesium, sulfur, silicon
- Micronutrients: iron, manganese, copper, zinc, boron, molybdenum, chlorine
Heavy Metals and Inorganic Contaminants
- The eight regulated metals: cadmium, mercury, arsenic, lead, chromium, copper, nickel, and zinc
- Hexavalent chromium as a speciated parameter
- Extended elements such as selenium, cobalt, antimony, thallium, beryllium, and vanadium when site history warrants
- Total cyanide and fluoride, plus soluble salts in saline or alkaline soils
Organic Contaminants
- Volatile organic compounds (VOCs), including benzene series and halogenated solvents
- Semi-volatile organic compounds (SVOCs) and phenolic compounds
- Polycyclic aromatic hydrocarbons (PAHs)
- Polychlorinated biphenyls (PCBs)
- Organochlorine, organophosphorus, and pyrethroid pesticides
- Total petroleum hydrocarbons (TPH) and petroleum fractions C6–C40
- Phthalate esters and other plasticizers
Biological Indicators
- Total bacterial count, fungal count, and actinomycete count
- Fecal coliforms and Escherichia coli
- Soil enzyme activity and microbial biomass carbon for soil health studies
Testing Methods
Sample Pretreatment
Field samples are air-dried or kept chilled for volatile-sensitive parameters, then crushed, quartered, and sieved, generally following the procedures of ISO 11464 or the applicable national method series. Elemental analysis requires digestion: aqua regia extraction (ISO 11466) recovers environmentally relevant metal fractions, while total dissolution with hydrofluoric acid-based mixtures or microwave digestion (HJ 832) is used for total content determination.
Elemental Analysis Techniques
- Atomic absorption spectrometry (AAS), flame and graphite furnace, for metals such as lead and cadmium (GB/T 17141)
- Atomic fluorescence spectrometry (AFS) for mercury and arsenic (GB/T 22105 series)
- Inductively coupled plasma optical emission spectrometry (ICP-OES) for multi-element screening
- Inductively coupled plasma mass spectrometry (ICP-MS) for trace and ultra-trace elements (HJ 680, HJ 803)
- Portable and benchtop X-ray fluorescence (XRF) for rapid in-situ and screening-level metal determination
Chromatographic and Spectrophotometric Techniques
- Headspace and purge-and-trap GC-MS for VOCs (HJ 605, EPA 8260D)
- GC-MS for SVOCs, PAHs, PCBs, and pesticides (EPA 8270E)
- GC-FID for total petroleum hydrocarbons and petroleum fractions
- HPLC and UV-Vis spectrophotometry for phenols, formaldehyde, and colorimetric nutrient assays
Classical Wet Chemistry Methods
Gravimetric methods determine moisture, organic matter (ASTM D2974), and particle size by hydrometer or pipette analysis. Potentiometric methods measure pH (ISO 10390, ASTM D4972) and EC. Kjeldahl digestion quantifies total nitrogen, molybdenum-antimony anti-colorimetry determines phosphorus, and flame photometry or AAS measures potassium. Titration and ion-selective electrodes cover chloride, cyanide, and fluoride. All measurements are supported by method blanks, spiked recoveries, parallel duplicates, and certified reference materials to satisfy ISO/IEC 17025 quality requirements.
Applications
Soil composition analysis data directly support technical and regulatory decisions across multiple sectors:
- Precision agriculture: soil testing and formulated fertilization programs that balance macronutrient and micronutrient inputs
- Environmental site assessment: Phase II investigations, contamination delineation, and human health risk assessment for land redevelopment
- Remediation projects: baseline characterization, treatment process optimization, and post-remediation acceptance testing
- Land management: soil quality grading, basic farmland protection, and cultivated land occupation–reclamation balance evaluations
- Engineering construction: evaluation of corrosivity, soluble salts, and suitability of borrow soil and backfill material
- Ecological research: long-term monitoring of soil carbon, nutrient cycling, and heavy metal background values
FAQ
How much soil sample is required for testing?
For routine physicochemical and heavy metal analysis, about 500 g to 1 kg of air-dried soil per sample is generally sufficient. VOC and SVOC testing requires 20–50 g of undisturbed soil collected with minimal headspace in pre-cleaned vials kept at 4 °C or below.
How should soil samples be collected and preserved?
Collect 3–5 sub-samples per plot in an S-shaped or checkerboard pattern, remove surface debris, and combine into a composite sample using the quartering method. Label containers clearly, transport them in coolers, and deliver them promptly, since volatile parameters typically require analysis within 7 days of collection.
What is the difference between total and available nutrients?
Total nutrient content (total nitrogen, phosphorus, potassium) reflects the overall reservoir after full digestion, whereas available nutrient content measures the extractable fraction that plants can absorb in the current season. Fertilizer recommendations are based primarily on available nutrient results combined with yield targets.
Which standards define soil quality and screening values?
In China, GB 15618-2018 sets risk screening values for agricultural land and GB 36600-2018 sets screening and intervention values for development land. International practice also references ISO methods for individual parameters and jurisdiction-specific guidance such as EPA methods for analysis.
How long does soil composition analysis take?
Routine fertility panels are usually completed within 5–7 working days. Full contaminant suites covering dozens of VOCs, SVOCs, PAHs, PCBs, and petroleum hydrocarbons typically require 10–15 working days, depending on sample load and confirmatory re-testing.
What should a professional soil test report include?
An accredited report from a third-party laboratory should state sampling information, testing standards and methods, detection limits, quantitative results, quality control data, and an evaluation against applicable screening values, issued with the laboratory's accreditation scope and unique report number for traceability.