Agricultural Land Soil Environmental Testing: Standards, Parameters, and Analytical Methods

Agricultural land soil environmental testing is a systematic process for evaluating the quality and safety of farmland by measuring heavy metals, pesticide residues, nutrients, and physicochemical properties against national and international standards. Testing performed in accordance with GB 15618-2018 and related method standards helps regulators, landowners, and agribusinesses identify contamination risks, safeguard food safety, and support sustainable soil management. This article explains the sample types, testing items, analytical methods, quality control procedures, and practical applications of farmland soil environmental monitoring.

Technical Overview

Agricultural land soil environmental testing refers to the collection, preparation, and laboratory analysis of soil samples from cultivated land, orchards, vegetable bases, and other agricultural use areas in order to characterize soil quality and quantify contamination risks. The primary regulatory benchmark in China is GB 15618-2018, the Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land, which establishes risk screening values and risk control values for key contaminants under different soil pH ranges and land use types such as paddy fields and other agricultural land.

The standard defines eight basic monitoring items — cadmium (Cd), mercury (Hg), arsenic (As), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn) — together with selected organic items such as hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT). Sampling design, sample handling, and data evaluation are governed by supporting technical specifications, including HJ/T 166-2004 for soil environmental monitoring, NY/T 395-2012 for farmland soil environmental quality monitoring, and internationally recognized procedures from ISO and ASTM where global comparability is required.

• Risk screening values: concentrations above which further investigation or risk assessment is warranted.
• Risk control values: concentrations above which strict risk control, restricted planting, or remediation measures are required.
• pH-dependent criteria: screening values are segmented into four pH bands (below 5.5, 5.5 to 6.5, 6.5 to 7.5, and above 7.5) because contaminant mobility and bioavailability vary with acidity.
• Land-use differentiation: separate criteria apply to paddy fields and other categories of agricultural land.

Testing Samples

Surface (Plow Layer) Soil Samples

The plow layer, generally 0 to 20 cm in depth, is the most frequently sampled horizon because it directly interacts with crop roots, fertilizers, and irrigation water. Composite samples are formed by combining multiple sub-samples collected along an S-shaped, diagonal, or grid-based route across a uniform sampling unit, typically yielding 1 to 2 kg of soil after quartering. This approach smooths out short-range variability and produces a representative average for the field.

Soil Profile and Subsurface Samples

When contamination is suspected to have migrated downward, profile samples are collected at fixed depth intervals, such as 0 to 20 cm, 20 to 40 cm, and 40 to 60 cm, using pits or mechanical corers. Profile data reveal vertical distribution patterns, distinguish recent deposition from geogenic background, and support risk assessment for deep-rooted crops and groundwater protection.

Paddy Field Soil

Flooded paddy soils develop anaerobic conditions that strongly influence the chemical speciation of arsenic, mercury, and cadmium. Samples are typically collected after drainage or between cropping cycles, and redox-sensitive parameters may be requested alongside the standard contaminant suite to support accurate interpretation against GB 15618-2018 paddy field criteria.

Greenhouse and Intensive Cultivation Soils

Protected cultivation systems such as greenhouses and plastic tunnels often receive heavy inputs of fertilizers, manures, and pesticides, leading to salinization, nutrient imbalance, and accumulation of copper, zinc, or organic residues. Testing programs for these matrices usually combine salinity indicators, nutrient panels, and contaminant screening.

Peri-Urban and Irrigation-Influenced Farmland

Farmland located near industrial parks, mining areas, highways, or historic wastewater irrigation zones carries elevated exposure risk from atmospheric deposition and contaminated water transfer. Sampling density in these areas is typically increased, and the analyte list is expanded to include site-specific contaminants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), petroleum hydrocarbons, and additional trace elements.

Testing Items

Testing programs are configured according to the monitoring objective, land use history, and regulatory requirements. A typical farmland soil assessment combines the following parameter groups.

Physicochemical Properties

• pH and electrical conductivity (salinity indicator)
• Soil organic matter and total carbon
• Moisture content and water-holding capacity
• Soil texture (particle size distribution) and bulk density
• Cation exchange capacity (CEC)

Nutrient Parameters

• Total nitrogen, alkali-hydrolyzable nitrogen
• Total phosphorus and available (Olsen) phosphorus
• Total potassium, available potassium, and slowly released potassium
• Secondary nutrients: exchangeable calcium, magnesium, and sulfur
• Micronutrients: available iron, manganese, copper, zinc, boron, and molybdenum

Inorganic Contaminants (Heavy Metals)

• GB 15618-2018 basic items: Cd, Hg, As, Pb, Cr, Cu, Ni, Zn
• Extended items: hexavalent chromium, selenium, fluoride, thallium, cobalt, vanadium, antimony, and beryllium, depending on local pollution sources

Organic Contaminants

• Organochlorine pesticides: HCH isomers, DDT and metabolites, endosulfan, heptachlor
• Organophosphorus and pyrethroid pesticides
• Polycyclic aromatic hydrocarbons, including benzo[a]pyrene
• Polychlorinated biphenyls (PCBs)
• Total petroleum hydrocarbons and phthalate esters

Testing Methods

Sampling and Sample Preparation

Sampling follows HJ/T 166-2004 and NY/T 395-2012, which specify grid-based or random point layouts, minimum sampling densities, collection tools free of target analytes, and chain-of-custody documentation. Samples are transported in inert containers, air-dried in clean environments, crushed, and passed through nylon sieves — commonly 2 mm for pH and nutrients, 0.25 mm for organic matter, and 0.149 mm for heavy metal digestion — to obtain the analytical fractions required by each method.

Heavy Metal Analysis

• Inductively coupled plasma mass spectrometry (ICP-MS) after aqua regia extraction or four-acid digestion, per HJ 803-2016 and HJ 680-2013, enabling multi-element determination at trace levels.
• Graphite furnace atomic absorption spectrometry (GFAAS) for lead and cadmium per GB/T 17141-1997.
• Flame atomic absorption spectrometry for copper and zinc per GB/T 17138-1997, chromium per GB/T 17137-1997, and nickel per GB/T 17139-1997.
• Atomic fluorescence spectrometry (AFS) for mercury and arsenic per GB/T 22105, providing high sensitivity for these hydride- and vapor-forming elements.

Organic Contaminant Analysis

• Gas chromatography with electron capture detection (GC-ECD) for organochlorine pesticides per GB/T 14550-2003.
• Gas chromatography-mass spectrometry (GC-MS) for organochlorine pesticides per HJ 835-2017, PAHs per HJ 805-2016, and PCBs per HJ 743-2015, using accelerated solvent extraction, ultrasonic extraction, or Soxhlet extraction followed by solid-phase or column cleanup.
• High performance liquid chromatography (HPLC) for selected thermally labile pesticides and PAH confirmation.

Physicochemical and Nutrient Analysis

• pH by potentiometric measurement in a soil-water suspension per NY/T 1121.2, ISO 10390, or ASTM D4972.
• Organic matter by potassium dichromate oxidation titration per NY/T 1121.6.
• Total nitrogen by Kjeldahl digestion, available phosphorus by the Olsen or Bray method, and available potassium by ammonium acetate extraction with flame photometry.

Quality Assurance and Quality Control

Reliable results depend on rigorous quality control, including method blanks, laboratory duplicates, matrix spikes, calibration verification, and analysis of certified reference materials. Accredited third-party laboratories operating under ISO/IEC 17025 management systems and holding national laboratory accreditation provide validated methods, traceable calibration, and defensible data reports suitable for regulatory submission and litigation support.

Applications

Agricultural land soil environmental testing supports a wide range of regulatory, commercial, and scientific objectives.

• Soil pollution status surveys and detailed investigations at national, provincial, and county levels.
• Categorization of farmland into priority protection, safe utilization, and strict risk control classes based on GB 15618-2018 exceedance assessment.
• Safe utilization programs, including soil amendment, low-accumulation crop variety selection, alternative water sources, and planting structure adjustment.
• High-standard farmland construction, arable land quality grading, and land remediation project acceptance.
• Environmental qualification of production bases for green food and organic certification schemes.
• Investigation of farmland surrounding industrial parks, mining zones, landfills, and historic sewage irrigation areas.
• Effectiveness evaluation of soil remediation and heavy metal passivation treatments through before-and-after comparison.
• Precision fertilization, soil improvement planning, and due diligence for agricultural land transactions and supply chain food safety audits.

FAQ

Which standard governs agricultural land soil quality in China?

GB 15618-2018 is the controlling risk control standard for agricultural land. It is complemented by monitoring specifications HJ/T 166-2004 and NY/T 395-2012, and by dozens of method standards for individual analytes. Construction land is assessed separately under GB 36600-2018, so the correct standard must be selected according to land use.

What is the difference between risk screening values and risk control values?

Risk screening values are thresholds used to filter out land that is essentially clean; results below these values generally indicate negligible risk, while exceedances trigger further detailed investigation or risk assessment. Risk control values are higher thresholds above which agricultural use is restricted and strict risk control or remediation measures, such as shifting to non-food crops or implementing engineered treatment, become mandatory.

At what depth should farmland soil samples be collected?

Routine monitoring targets the plow layer at 0 to 20 cm, which reflects the root zone and fertilization influence. For paddy fields, orchards, or suspected deep contamination, sampling is extended to 40 cm or deeper through profile sampling to characterize vertical migration.

How many sampling points are required per field?

Point density depends on monitoring purpose and unit size. Detailed investigations often use grid layouts ranging from several hundred meters per grid down to finer spacing near suspected sources, with each grid represented by a multi-point composite sample. Historical pollution surveys and site-specific assessments apply denser layouts than routine surveillance.

How often should agricultural soil be tested?

Routine monitoring is typically performed every one to three years, while risk-control farmland, bases supplying fresh agricultural products, and newly designated protected areas may require annual testing. Remediation projects sample before, during, and after treatment to verify effectiveness.

What does a basic testing package include?

A standard package generally covers pH, organic matter, and the eight basic heavy metals (Cd, Hg, As, Pb, Cr, Cu, Ni, Zn), with optional addition of HCH and DDT. Extended packages add PAHs, PCBs, petroleum hydrocarbons, organophosphorus pesticides, and site-specific trace elements based on surrounding land use.

How should a testing laboratory be selected?

Choose accredited third-party laboratories that hold national laboratory accreditation to ISO/IEC 17025, use national or international standard methods, participate in proficiency testing schemes, apply certified reference materials for quality control, and deliver full documentation of sampling, analysis, and data evaluation suitable for regulatory acceptance.