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Organic produce

Differentiating organic produce from conventional produce by determining which fertiliser was used

agroisolab organic poster

The differentiation between organic and conventional produced products using current analytical methods can still be challenging. This is due to the fact that the nutritional composition of organic and conventional agricultural products is more or less identical.


Presently there are three types of method that can be used to differentiate organic and conventional products, each with their own strengths and limitations (see right).

3 current methods to check the authenticity of organic products


• GMO analysis – detects Genetically Modified Organisms


• Pesticide/residue analysis – detects  acceptable / unacceptable agrochemicals / pharmaceuticals


• Isotope analysis – detects the method of fertilisation used on crops (15N/14N)

Tracing problems back to their roots – the stable isotope method

There is considerable advantage in the stable isotope method as it offers the opportunity to trace problems back to their roots in a range of products from fruit to meat.


The stable isotope method exploits the fact bioelements (hydrogen, carbon, nitrogen, oxygen and sulfur) exist in two stable variants in natures / isotopes. For example, in addition to the “normal” nitrogen nature also has a heavy version of nitrogen (1 additional neutron). This subtle, but profound difference offers the opportunity to track produce.


Since 1974, it is well known that organic fertilisers such as composts, manures and green manures show greater enrichment of heavy nitrogen (15N) than conventional mineral fertilisers. Organic fertilisers typically have nitrogen ratios of +10‰ +/- 4 in comparison to mineral fertiliser which has nitrogen ratios of roughly 0 ‰ (Shearer 1974) (see Figure 1).

Nitrogen ratios from various fertilisers

The science behind checking the fertilisation source using 15N/14N analysis

The enrichment of heavy nitrogen (15N) in biomass derived fertilisers (compost, manure, bonemeal) is the product of metabolism. Transaminase, an enzyme that exists in all organisms and is involved in protein/urea metabolism, prefers heavy nitrogen (15N) as opposed to normal nitrogen (14N). Further heavy nitrogen enrichment in manure based fertilisers can be attributed to the preferential volatilisation of 14N ammonia (Sturm et al. 2011). As a result, biomass derived fertilisers are enriched in heavy nitrogen and can be easily differentiated from mineral fertilisers (figure 1).


Nitrogen ratios from the fertilisers are reflected in crops grown in the fertilised soil; if the soil was fertilised with biomass derived fertilisers (organic fertilisers) which show the enriched heavy nitrogen signature, this will be evident in the crop (Yoneyama 1990). The reverse also applies, if a crop is fertilised with mineral fertiliser (15N/14N = 0‰) the nitrogen ratio of the crop will reflect in this signature too.


As the use of mineral fertiliser is strictly prohibited in organic farming, the use of isotope testing the nitrogen in fertilised organic products offers countless prospects in terms of authentication, surveillance and the detection of product mislabelling in products declared as organic.


To this date, there is a wealth of peer-reviewed scientific literature (Choi, 2003, Nakano 2003, Bateman 2007, Rogers 2008, Sturm 2011) demonstrating and supporting the evidence that analysing nitrogen ratios (15N/14N) in agricultural produce offers excellent opportunity to determine organic provenance in many products.

Quick guide to the difference in stable isotope ratios in organic and conventional crops:

The practical approach – how to make use of 15N/14N isotope testing

The stable isotope method as an authentication/surveillance tool is most powerful when used in conjunction with knowledge of the declared fertilisation method used to produce a crop.


It has to be considered which agricultural products this technique is best used with. Generally the best products that show the greatest differentiation between organic and conventional varieties are the shallow root plants that have a high demand for fertilisation. However, when used appropriately, this technique can be used in finished products such as eggs.

Organic pot IMG_8514

The use of reference databases to authenticate products


Agroisolab GmbH prefers to establish databases for each agricultural product to get the best overview which ratios of nitrogen are expected to be observed in organic and conventional produce.


Furthermore any information about the fertiliser used to cultivate the test sample is helpful draw accurate conclusions from the report.

Testing products in the absence of a reference database


If there is no direct database of organic/conventional products available to compare a test sample to, it is only possible to evaluate whether the product was produced using organic (biomass-derived) fertilisers, leguminous plants/nitrogen fixing cultures, or mineral fertiliser.

Further assessment of samples that return with ‘abnormal ratios’


Origin testing

Especially in the case of mislabelled/abnormal samples, there is a high risk that the sample does not originate from its declared origin. Therefore it is recommended to check the origin of the sample as well.


For origin testing, the following isotopes are normally used to check the origin:

  • Hydrogen D/H (regional parameter of water)

  • Carbon 13C/12C (climate parameter)

  • Sulfur 34S/32S (geological parameter)


GMO testing

Where applicable, or where the risk of GMO adulteration is high, further evidence of non-organic status should be sought from GMO analysis. One example would be if maize/corn/prairie meal was discovered to have 15N/14N ratios more negative than 0‰, it is possible the product has been diluted/substituted with GMO maize. Agroisolab GmbH works closely with a network of labs that can be recommended to carry out this test.


Pesticide/residue analysis

Where applicable, it is recommended that further evidence of non-organic status is also obtained from pesticide/residue analysis. It is possible for mislabelled organic products to be fertilised with mineral fertiliser and not have non-compliant pesticide residues.  Agroisolab GmbH works closely with a network of labs that can be recommended to carry out this test.


Further product/ingredient testing

In the event where finished products such as eggs are marked as organic are discovered to have nitrogen signatures that give over 95% probability they are not organic, there may be several reasons for this:


  • This is a conventional product being passed off as organic

  • This is a product from an organic production system where non-organic feed is being fed to the animals

  • This is a product from an organic production system that is being diluted with conventional products

Further investigation is required to reach the root of the problem, we are happy to offer advice about how best to investigate and resolve the issue.