Which is Better, Bray-1 or Mehlich-3?

(…another agronomy rant from another agronomist at ALGL, David Henry. Once again, this is not directed at any particular entity or person, just a response to an often-misunderstood topic in the industry.)

Asking which phosphorus extraction (Bray-1 or Mehlich-3) is “better” is like asking if inches or centimeters are better at measuring length. You are measuring the same thing, just using a different scale.

In fact, most people who work routinely work with soil test data, likely have never seen an actual Bray-1 value. This is because the Bray-1 and M3 phosphorus extractions are very well correlated to each other. This means that given either value, you can calculate what the other is with a high degree of certainty. As a result of this, most commercial soil labs adopted the M3 extraction as their routine extraction method 2 or 3 decades ago but can still report a Bray-1 value.

Why is this? You might ask. Well, the M3 extraction is also very good at extracting other nutrients. Like nearly all of them that we are interested in when growing plants. From a laboratory efficiency standpoint, M3 is far superior to Bray-1. For the end user, it really does not matter. As long as you know which value you are working with and are using the appropriate interpretations and equations, one extraction will not give you better crop production results over the other.