Chromatography
Chromatography allows for a biological analysis of soil or solid organic products.
Context
Biology is the component of the soil that links soil chemistry and plant chemistry. This means that biology has a direct and significant impact on plant nutrition, development, and health. Moreover, biology is responsible for the stable structure of the soil. It is the bacteria and fungi that bind the organic and mineral particles of the soil, creating micro and macro-aggregates that allow the soil to have good porosity. This porosity in turn allows better infiltration and water storage, good air circulation in the soil, but also supports the development of a diverse biology. Indeed, the different pores allow the development of aerobic and facultative anaerobic biology. Of course, biology is also responsible for recycling and releasing nutrients for plants in an assimilable form. However, be careful not to focus only on earthworms or only on fungi and bacteria. There is a whole complete and complex network in the soil, which must be well developed so that everything works together and all functions are present.
In a biologically well-functioning soil, plant nutrition does not depend solely on the chemical characteristics of the soil.
Objective
Biological analyses can have different objectives. Depending on what is sought, one must choose the analysis or analyses that are appropriate. Most analyses are not reserved only for soils but can also be used for organic products (composts, manures, compost teas…). It is important to choose the analysis that best meets the needs and the type of sample.
Chromatography is used to analyze the efficiency and functioning of the biology present in the soil or solid organic products (composts for example). For soils, it is not always necessary to perform a biological analysis annually. It is important to monitor changes over time to verify the impact of agricultural practices and adjust them. Other factors, such as climate, can have a considerable impact on biology.
Using a practice that in theory is positive for the soil and biology, is not necessarily so in practice.
When solid organic products are used, such as composts, it is important to check their quality, which is notably a direct consequence of the composting method. Depending on the type of product, certain results are expected. For example, a compost made by the Johnson Su or Ingham method should be an aerobic product. On the chromatogram, air and structure should therefore be visible. Also, depending on the products, they should be rather bacterial, fungal, or balanced. This can be verified by chromatography.
Another interesting tool for organic products is the microscope, which allows checking that important groups of organisms are present at different stages of composting.
The analysis
Chromatography is a comprehensive analysis that informs on:
- Aeration: stable structure.
- Retention of nutrients.
- Bacterial diversity and activity.
- Fungal diversity and activity.
- Decomposition and fixation of organic elements.
- Integration of organic compounds with mineral compounds.
- Dynamics of biological evolution (if the analysis is performed on 2 types of filter paper).
It is a qualitative analysis, provided with a rating to position oneself (depending on the provider).
Chromatography is an analysis whose first trials were conducted in the 1850s by Friedlieb Ferdinand Runge, then developed by Ehrenfried Pfeiffer in the 1950s. It is performed on round Whatman filter paper. This filter paper is prepared with silver nitrate which reveals colors. The soil, after being dried, is mixed with sodium hydroxide. This releases the organic elements, which are of interest for this analysis. This soil solution is drawn onto the round filter paper. After a drying period in the light to reveal structures and colors, the chromatogram is ready to be analyzed.
The operation can be performed on 2 types of filter paper:
- Whatman No. 1 paper gives an overall view, a first glimpse of biological activity.
- Whatman No. 4 paper gives a more detailed view, more precise.
The evolution between No. 1 and No. 4 gives the biology dynamics: is it a positive or negative dynamic? Is there an improvement or deterioration? This dynamic gives a good indication of the effects of practices.
Results
Depending on the chosen provider, the chromatogram is delivered with a rating, explanations, and recommendations.
Example of soil chromatograms
This rating was performed by Gässler SAS:
The first chromatogram shows a soil poor in biological activity:
- The colors are pale: the organic material is not decomposed into humus. This also explains the lack of bacterial activity (periphery of the chromatogram).
- There is no white center: there is a lack of air in the soil structure. The soil is poor in biological aggregation. Yet this is essential for the development of beneficial and diverse biology.
The last chromatogram shows a soil with good biological activity:
- The first indication is a much more complex chromatogram in structure than the first.
- The well-visible white center here indicates that the soil structure is good, there is good aggregation allowing air retention in the soil.
- The clouds visible on the periphery show good bacterial activity.
- The radial lines, linking the periphery and the center, indicate good fungal activity. They cross the entire chromatogram: fungi are sufficiently developed and active to allow the binding of organic elements with mineral elements of the soil.
Example of compost chromatograms
This rating was performed by Gässler SAS:
For compost, it is important to take into account the stage of decomposition. Is the compost sold as a finished product? Here, it is the case.
The chromatogram on the left shows a poor composting process: the continuous line on the periphery indicates that the organic material is not well decomposed: it is a coarse compost. It has not been aerated: absence of white center. This does not allow the different organisms to develop and perform their functions.
Conversely, the chromatogram on the right shows different structures. There is still raw / undecomposed organic material. This is indicated by the presence of the thin continuous line on the periphery. However, it is a composting that has been well conducted, allowing beneficial biological life to develop:
- The white center indicates good aggregation.
- The periphery indicates good bacterial activity, allowing effective integration of humus.
- The radial lines show good fungal activity.
Protocol
First contact the intermediary you wish to work with, so they can provide you with the precise protocol and the information sheet to be submitted with the samples.
When to sample?
- Soil:
Ideally, sample in spring or autumn. Avoid periods that are too dry / too wet and too hot / too cold. What is important is to always sample at the same period if you are making comparisons over time and/or space.
- Compost:
- If you make the compost yourself: Sample regularly, at different stages of the process to ensure everything is going well and adjust if necessary.
- If you buy the organic product: It is normally stabilized. You can therefore sample upon receipt, then over time to check the stability of quality.
Where to sample?
- Soil:
Choose homogeneous zones in your plot in terms of texture, drainage, management. Optionally compare zones where plants grow well with zones where plants grow less well. Sample at several locations in your plot, then mix all samples well. Send 200 g of soil.
- Compost:
- If you make the compost: Sample at different locations where maturity is the same. Mix the different samples of the same sample well, then send 200 g. You can make several samples to compare different parts of the pile.
- If it is a purchased product, sample several locations and mix.
What to sample?
- Soil:
Sample to 10 cm depth. Remove the first cm to avoid influences from inputs and remove any large residues.
- Compost:
Remove at least 10 cm of surface compost before sampling.
Sending the sample
The sample must be dried before sending, at 55 °C for 12 h. Send about 200 g of sample, placed in a zip-lock bag. Do not place paper in the bag as it may deteriorate and contaminate the sample. Label the bag with the sample name.
Frequency
- Soil:
It is good to return to the same plot every 2 or 3 years, to monitor changes. This also allows spreading the plots you want to analyze over 3 years.
- Compost:
- If you perform composting: Analyze the compost at different stages of the process to manage evolution best.
- With a purchased product, which is stabilized: Analyze upon receipt then 1 year later, to ensure its stability.
Points of attention
For analyses, as for most analyses, it is essential to always work with the same people and therefore the same laboratories. It is pointless to compare results from one laboratory to another: the sample sent is not the same, the interpretation and especially the rating criteria may differ.
Do not hesitate to contact different providers to ask questions, compare, and choose the partner and method that suit you best.
Cost
As an example, at Gässler SAS, the analysis performed on the 2 types of papers, with rating, interpretation, and recommendations costs €100.
Source
This article was written with the kind contribution of Marie-Thérèse Gässler from Gässler SAS.
