The ISO 14870 Soil quality - Extraction of trace elements with buffered DTPA solution standard, published by the International Organization for Standardization (ISO), describes a method for extracting trace elements from soil samples using a buffered diethylenetriaminepentaacetic acid (DTPA) solution. This method is primarily applied to estimating the availability of copper, iron, manganese, and zinc for plants growing in soils.
This standard is preferably suitable for soils with a pH greater than 6. Potentially toxic elements such as cadmium, chromium, nickel, and lead may also be detected in the extracts. In soils containing one or more of these elements in large quantities, exceeding the complexing capacity of DTPA may reduce the efficiency of extraction of any of these elements.
This standard does not specify methods for measuring trace elements in extracts.
In principle, the soil sample is extracted at 20 degrees Celsius, under gentle shaking conditions and with a soil:solution extraction ratio of 1:2 (m/V), in a mixed buffered solution (pH = 7,3) containing soluble trace elements, triethanolamine, calcium chloride, and diethylenetriaminepentaacetic acid (DTPA).
Determination of trace elements in extracts can be performed using flame or electrothermal atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, or other related techniques. Due to the relatively high extraction rate, obtaining sufficient extract solutions in soils with high absorption capacity can be challenging.
As a laboratory sample, a portion of air-dried soil samples, pre-treated according to ISO 11464 standard and passed through a 2 mm sieve, is used. A separate portion of the sample is used to determine the water content according to ISO 11465 standard.
The extraction procedure is as follows: Using a plastic spatula, 10,00 g of the laboratory sample is weighed and transferred to a 100 ml container. 20,0 ml of extraction solution is added using a pipette or dispenser. The container is tightly closed and shaken using a shaker at 20 degrees ±7 degrees Celsius for 2 hours. A portion of the extract is poured into a centrifuge tube and centrifuged at 3000 g for 10 minutes. The supernatant is filtered using a filter. After the phases are separated, the extract is transferred to a polyethylene bottle and analyzed within 48 hours. In each batch of analysis, blank extractions are performed using the same procedure but without the soil sample.
In environmental science and agriculture, assessing soil health is of paramount importance for sustainable agriculture, land management, and ecosystem conservation. A key aspect of soil analysis is determining the bioavailability of essential trace elements—micronutrients such as copper, iron, manganese, and zinc—that plants require in small amounts for optimal growth. The ISO 14870 standard provides a standardized method for extracting these trace elements from soil samples, enabling accurate estimation of their plant-available fractions.
Soil is a complex matrix influenced by factors such as pH, organic matter content, and mineral composition, which affect how trace elements are bound and released by plants. Traditional total element analysis often overestimates availability, as it includes forms that are not biologically available, found in minerals or organic complexes. The ISO 14870 standard presents a selective extraction technique using a buffered diethylenetriaminepentaacetic acid (DTPA) solution, a chelating agent that mimics root exudates and dissolves only the variable, plant-accessible fractions of these elements.
The primary aim of this standard is to support agronomic decisions, such as fertilizer recommendations and deficiency corrections, by providing reproducible results in laboratories worldwide. This standard ensures consistency in environmental monitoring and compliance with regulations. Specifically, this method is designed for neutral to slightly alkaline soils (pH 5,5-7,5) where micronutrient deficiencies are common.
The ISO 14870 standard is widely used in the following areas:
However, limitations exist. The efficiency of the method decreases in highly acidic (pH up to 5,5) or calcareous soils where alternative extractants such as Mehlich-3 may be preferred. In soils with excessive trace elements, DTPA saturation can occur, underestimating its availability. Furthermore, this standard focuses only on extraction and not on subsequent measurements, which necessitates integration with other standards such as ISO 11885 for water quality parallels.
With global food demand increasing and soil degradation affecting 33% of arable land, ISO 14870 and similar standards play a critical role in precision agriculture, according to UN estimates. By standardizing DTPA extraction, it promotes international data comparability and supports policies such as the EU's soil monitoring directive. Recent approvals, along with adaptations for automated systems that increase efficiency in commercial laboratories, reflect the enduring importance of the ISO 14870 standard.
The ISO 14870 standard is important because it is a globally accepted, scientifically validated, and practical standard that enables farmers, agricultural engineers, researchers, and regulators to reliably know how much zinc, iron, manganese, and copper are available in the soil, especially in the vast areas of neutral to alkaline soils that feed a large portion of the world's population.
In conclusion, the ISO 14870 standard is more than just a technical protocol; it is a tool that connects soil science with sustainable practices and enables the accurate measurement and utilization of hidden trace element richness in soils. For those working in agriculture or environmental fields, adopting this standard provides insights into soil fertility that directly impact productivity and the health of the planet.
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