Extraction Methods and Data Comparison

There are many types of extraction methods, formulations and practices a laboratory may use to provide the best data possible. This, of course, depends on the customer’s needs and goals. Often, the industry standards will remain steady to provide consistent data sets of soil data. This is important in monitoring trends, patterns and completing long-term goals.

Occasionally, a new concept will emerge. This is also important. A great example is when Mehlich-3 came to light in the early 1980’s. The Mehlich-3 extraction allows laboratories to extract multiple nutrients with one step. This extraction not only provides more consistent results, but it benefits the consumer with more affordable testing.

To use one method of extraction as an example would be a Bray-1 phosphorus test. This was the standard since the 1940s and offered decades of research studies for calibrated recommendations. In fact, it is set at such a standard that many prefer Mehlich-3 phosphorus results to be calculated back to Bray-1 to interpret the results.
When a new method is being utilized, like the Bray-1 and Mehlich-3 scenario, it is especially important to not compare analysis results of one method to the other.

This will lead to much confusion when comparing different data sets. When comparing past analyses to the new current method of extraction, they must be calculated. Each laboratory may have their own set of calculations to switch Mehlich-3 back to a Bray-1. This is why it is very important to utilize a reputable laboratory for long-term data analysis. There are several different extraction and testing methods emerging in the marketplace. This is especially difficult to compare to past results that use different extraction methods.

To use a new extraction method for a soil sample it is necessary to use the originator’s interpretations and recommendations. A phosphorus nutrient analysis extracted by water, for example, cannot be compared to a phosphorus level extracted by Mehlich-3 for trending data purposes or finding patterns. It would be as the saying goes, “comparing apples to oranges”. This would be a fresh slate of information to be used with the originator’s set of recommendations.

Stronger acid, or extractant, can be used to show higher nutrient levels, but without calibrated recommendations that suit your region, they cannot be used with confidence. What is important is to use the method that is best for your soil, that will provide what is most plant available and has calibrated data to give agronomic recommendations.