The reason behind the many different soil testing methods

Superficial glances at soils generally all lead to the naive conclusion that all soils are more or less the same. That they all have the same soil constituents: clay/sand, organic matter, carbonates, salts, etc and the same purpose: delivering nutrients to plants by root uptake. However a more detailed look will show you that soils are really divers and difficult to compare. E.g. the clay fraction of a soil may consist of different types of clay minerals. These clay minerals may have a different structural and chemical composition, different chemical bindings with nutrients and a different binding strength depending on pH, EC…

Most advisors, agronomists, plant nutritionists and soil fertility specialists don’t want this detailed information as they are more interested in a general characterization of agricultural soils based on:

-        the amount of plant nutrients which are released from a soil when chemicals are added.  Examples of chemicals that are used : e.g. water, salt solutions, acids, hydroxides, complexing and buffering agents and mixtures of two or more of these chemicals.

-        the relationship between the amount of plant nutrient released after addition of chemicals  and test crop response like yield, growth rate etc. in pot or field experiments

That is why the wet chemistry methods that extract an amount of nutrient that relates best to crop response is the preferred soil testing method.  

The SoilCares Golden Standard Laboratory where samples from around the world are analysed using traditional wet chemistry techniques.

The relationship between nutrient extraction and crop response is strongly dependent on the chemical composition of the soil, the test crop used and the method of experimentation. Therefore, often, experiments with different soils, different crops, different plant nutrient etc will often lead to a different optimal soil testing method.

The specific binding forms of nutrients in the soil and the specific interactions provoked by the addition of chemicals to the soil with these binding forms are the reason why there are so many, specific soil testing methods around the world.

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At SoilCares we do not use chemicals but sensor technology to facilitate soil testing with the Scanner and the Lab-in-a-box. The sensors determine the presence of nutrients in the soil but also its chemical bindings. With the information provided by these sensors, we get a much better knowledge on how plant nutrients are bound in the soil and whether or not they are available for plant root uptake.

The SoilCares Scanner using NIR infrared spectroscopy

SoilCares relates this sensor specific information to the results of numerous soil testing chemicals or soil testing methods.  E.g SoilCares tries to relate sensor information to at least 4 K fractions: total K content, K bound at the cations exchange complex, acid soluble K and water soluble K.

Thanks to the sensor technology SoilCares gets a much better understanding of nutrients fractions in agricultural soils and availability for plant growth. With this information the applications of fertilizers can be optimized and that is the way SoilCares contributes to a more efficient and sustainable food production.

Article written by Peter van Erp, head of SoilCares Research.

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