Ca:Mg Ratios

Bill Liebhardt (wcliebhardt@ucdavis.edu)
Wed, 18 Feb 1998 11:29:55 -0800

It has been interesting to see the dialog on this subject. I think I would
like to provide some information that might help or maybe it will just muddy
up the water. It will be somewhat my personal experience as a person trying
to make sense of the science and art of soil testing over many years of
work. In 1968 when I worked in the fertilizer industry I went to a training
session and was first exposed to the philosophy of the cation balance
between Ca, Mg, and K. It sounded OK to me and made some sense to have a
balance in the soil. At that time I somewhat excepted it and went on with my
work assuming that there was experimental evidence for this theory of
dealing with soil testing. Later on at at the University of Delaware I set
up an experiment that had zero, one and four tons of lime per acre using
dolomitic lime, calcitic lime, and a mixture of the two in a factorial
experiment with 0, 40 and 120 pounds per acre of potash<K20>. The
experiment went for 11 years while I was there. In the later six or seven
years of the experiment when the treatments were well established the data
showed on sandy coastal plain soil with corn and soybeans that the
philosophy of the Basic Cation Saturation Ratio did not operate<you did not
need the specific ratios this concept called for> with respect to yield.
With the range of treatments that were in this experiment we had wide ranges
of Ca and Mg saturation values as well as ratios. I did not set out to
prove or disprove this philosophy at the start of the experiment but when I
saw how this was being used particularly by the commercial soil testing
establishment I saw a need to try to find out how this all got started.

In the 70's and 80's many commercial labs were using this philosophy or the
soil build up and maintenance philosophy or a combination of both which
almost always resulted in fertilizer being added even when it was not
needed. This was also true with some land grant soil testing labs. Many
land grant labs used the sufficiency level approach which basically says you
test for a nutrient and if lacking you apply that nutrient. A number of
experiments were done in that time that compared fertilizer recommendations
of labs with very different philosophies and invariably they showed the
yields to be the same but the cost of the nutrients varied considerably,
with the cation balance and soil build up and maintenance being more
expensive by quite a bit.

Good soil testing in my opinion is based on the idea that you have field
data to support your nutrient recommendations. This means that you have
done research with similar soils and crops so that when the farmers sample
comes it can be compared to some research on similar soils and crops. That
is the theory or basis of soil testing. There is much lacking in most
states with regard to field calibration data and it is not a perfect world
by any means.

Now back to the cation balance story. When I began to see the data in my
experiment I wanted to find out where this cation balance story started.
After reading the trail first lead to people at Rutgers who had done an
experiment. People there proposed the concept of the ideal soil that had
certain amounts of CA, Mg and K. They took 20 soils from New Jersey<work
was done in the 40's> and added various amounts of Ca, Mg, and K. They
considered the ideal soil to have 65% CA, 10% Mg and 5% K. They found it
very difficult to get the ratios they wanted. They dropped the idea I was
told by people at Rutgers as not being practical.

Another part of the story came from people at the University of
Missouri-they used the cation balance theory in their soil testing program
in early 80's when I was attempting to get to the bottom of this story. I
called the soil testing lab at the University of Missouri and eventually
after talking to a number of people was told to talk to a Dr. Grahm who was
then retired. I called him and had a very pleasant conversation with him
about the data I had in Delaware and asked him how the use of the cation
balance came into use in Missouri. He said that he developed it for use on
Missouri soils. I asked him how he developed this, what research did he
have or information that I could cite or use. He then told me the story
which I found to be very interesting. He said that he sat down at his desk
after thinking about this for some time and came up with ratios that made
sense to him based of the clay minerals in Missouri soils. He based this on
his knowledge of Missouri soils and an article he had by a Dutch soil
scientist by the name of Hissink. He said it was not based on field
research but that it was he best estimate of how things out to be in Missouri.

This then showed me that it was not based on hard data, research or evidence
that I thought it should be. I have seen lots of fertilizer recommendations
not based on good data but here was a philosophy being used all over the
country and in my opinion it is a house of cards-it does not have a solid
foundation that is research based. This is the story as I know it. There
maybe other pieces out there that I do not know and I would like to hear or
see the evidence that any one has to support this cation balance concept.
If you have it you should come to the table with it. I know many people use
the concept and say it works but I have yet to see any evidence that will
stand up to review. It is somewhat amazing to me to see the basis for such
concept be so lacking but yet go so far but I guess that is life.

So my challenge to you supporters of this is to come forward with your
information whatever it is and let all of us see it. If there is silence I
will know the answer.

Best Wishes to all,

Bill

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* Bill Liebhardt, Director SAREP *
* 1 Shields Avenue *
* University of California, Davis CA 95616 *
* Phone: 530-752-2379 *
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* email: wcliebhardt@ucdavis.edu *
* WWW: www.sarep.ucdavis.edu *
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