In the article "Phosphorus Levels Can Make or Break High Yield results" by Darrell Smith which appeared on www.Agweb.com on October 23, 2017, Ken Ferrie, Farm Journal field agronomist, made the following statements:
"Soil tests do not tell you exactly how many pounds of phosphorus are in your soil. The results are indicators you can use to try to predict how much phosphorus will come out of soil, and how easily. Soil is a dynamic medium in which microbes are constantly changing phosphorus from plant-available to plant-unavailable and back again.
There are various ways to test soil for P availability. Each test has pros and cons, depending on your area and the soil types you deal with."
Growers Chemical Corporation has suggested to producers since 1955 that the soil test is only a guideline and proof positive of absolutely nothing. So when Ferrie suggests to farmers that the soil test is only a guide because the soil is a dynamic media, we are in agreement. The various soil extraction methods can indicate to a certain degree for the producer how much P may be present in the soil; however, the amount of P that the plant can actually utilize is still a function of the soil's microbiological life.
This microbe activity is why the agricultural industry is seeing new soil testing methods being introduced to the industry. These methods are trying to show the activity of the soil's microbiological life. In previously written articles Ferrie has suggested that these new testing methods are not of the accuracy they had hoped they would be. (See The Growers Solution Late Fall, 2015 Volume 28 Issue 5 "The Test Quest: What Soil Health Tests Really Tell You.")
Because of the problems with the biological tests along with their expense, Ferrie is suggesting that when examining P on your soil test, other parts of the soil test need to be interpreted to try and make sense of the P number. Growers Chemical Corporation would agree to a certain extent if the focus returns to the key element, which is calcium (Ca).
Since 1955, Growers Chemical Corporation has focused on the Ca volume in the soil test because of its important influence on the microbiological life in the soil. So, when looking at a soil test, the Ca to magnesium (Mg) ratio should be considered when trying to figure out the amount of P that is going to be released by the soil's microbiological life. For example, a soil with a very high P reading which contains an imbalanced Ca to Mg ratio, the amount of available P from that soil could be less than for a soil with a low P reading, but has an excellent Ca to Mg ratio.
As Growers Chemical Corporation has suggested since 1955, that the proper interpretation of the soil test requires test plots to make the interpretations. The new high technology terms are "Test and verify."
This is an excerpt from the Early Fall Growers Solution (2018) written by Jim Halbeisen, Director of Research.
Signup for our newsletter to stay in the loop
