As the use of relatively cheap fertilizers snowballed midway into
this century, there must have been considerable desire among
university agronomists to quickly develop systems by which they could
scientifically recommend the use of fertilizer.
My guess is that initally there was a real lack of data from fertilizer
response field trials and so recommendation systems like cation balancing
were hit upon as a quick way to make a "scientific" prediction of
fertilizer need. As time progressed universities accumulated large amounts
of field data and had a basis for switching over to "sufficiency"
recommendations.
So...without extensive field data and closer affiliation with fertilizer
dealers, many private labs have stuck with cation
balancing theories... makes sense to me...
I would also suggest that it has taken considerably longer for field
trial based rational recommendations for pesticides (i.e. IPM) to be in
widespread use than for fertilizer.
The biggest problem that I see with the current use of cation:balancing is
that the recommended ratios are being touted as applicable to all soils.
It seems to me that if the goal is to get the ideal ratio of Ca and Mg
into a crop, it should be the ratio of Ca:Mg in the soil solution that
is really the issue not the base saturation ratio on CE sites. Different
soils have very different mineralogies and thus have different affinities
for base cations. One base saturation ratio across many soils will lead to
many to different ratios of cations in the soil solution.
A quick search in the library tonight turned up an article that discusses
this issue.
Soil properties affecting the proportionate amounts of Ca, Mg and K
in plants and in HCl extracts. Adolf Mehlich Soil Science Vol 62 pg 393.
I believe the year was 1940. The article discusses cation ratios and is
followed by a lit cited
section that includes many other articles that appear to discuss cation
ratio theories.
I also observed that a number of articles including some by W.A. Albrecht
investigated the effect of different base cation levels on amino acid
levels and ratios in crops. There appeared to be evidence that amino
acid synthesis in plants is effected by base cation levels in
soil.
With the vast breakthroughs in biochemistry that have occured
since 1940 we must surely know more about base cation effects
on crop protein quality than we did 50 years ago... right ???
What do we know ???
So in summary, as Bill L suggested, I think that soil test
recommendations that are of
consistent value must be derived from field trials... if
optimal cation ratios for crop quality on particular soil types actually
exist...lets figure this out using field trials...
One set of cation ratios for the whole country defies basic scientific
understanding of the variability of soil...
Joel Gruver
U of MD, Soil Quality research
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