First of all, thanks to those of you who responded to my inquiry on cation
balancing and Ca:Mg ratios, either via the list or directly. With the
assistance of Ray Weil's comments and some information from Bill Liebhardt,
I've been able to dig up some (not all) answers to questions I raised and
others that Ray brought up in his first response. It turns out that there
has been some research at land-grant universities to address this issue.
Bill Liebhardt conducted research in Delaware during the 1970s to test what
he called the "Basic Cation Saturation Ratio Concept" for field crops. His
justification for the research was that two approaches to soil test
interpretation were in use: 1) sufficiency levels of available nutrients
(SLAN) and 2) basic cation saturation ratios (BCSR). The first was/is used
by university laboratories while the latter was/is used by commercial
laboratories.
In Liebhardt (1981) he reviews some of the early literature on the concept
and credits Firman Bear and other researchers from New Jersey during the
1940s with proposing it. I looked up some of the Bear et al. references and
found William Albrecht was indeed mentioned. However, Albrecht was cited
not as the founding father of the concept but rather for justification of
some laboratory methods. In these papers by Bear and associates, the ideal
soil was defined as having an exchange complex saturated with 65% Ca, 10%
Mg, 5% K, and 20% H (Bear and Toth 1945). This is based upon greenhouse
studies with alfalfa in an array of New Jersey soils.
Liebhardt went on to cite other studies from the 1930s and 40s that found no
relationship between Ca:Mg ratios and yield. And from his own research,
Liebhardt concluded, "wide ranges of Ca:Mg satisfy nutrient requirements of
corn and soybean" provided the pH is maintained at 6 or slightly less to
prevent Mn deficiency. Similarly, Eckert and McLean (1981) conducted a
growth chamber study with German millet and alfalfa under a range of cation
ratios and concluded that "balance of cations in the soil was unimportant,
except at the extremely wide ratios where deficiencies in one element were
caused by excesses of others." And Reid (1996) conducted a study in the
1970s to determine the effects of lime and Ca:Mg ratios on alfalfa and
birdsfoot trefoil and concluded that "ratios ranging from 267:1 to 1:1 had
no significant influence on yields of either species" but that maintaining a
pH at about 6.5 resulted in the highest yields. The general message from
these studies is that adjustments to the Ca:Mg ratios per se do not affect
crop yield except in extreme cases, but that the addition of Ca may improve
yields if the soil pH is lower than the optimal range.
All of the studies mentioned, however, approached the issue from a soil
fertility point of view. Many proponents of cation balancing claim that the
benefits of adding Ca are due to the long-term effects on soil structure
which promote root growth and may subsequently affect N use efficiency and,
perhaps, root diseases. This may in fact be the case in soils with poor
structure - where N use efficiency is reduced because of poor root growth or
because of denitrification from anaerobic pockets. But in soils with good
structure I still don't see the logic in adding Ca.
Ray mentioned that blossom end rot should be apparent on our tomatoes if
there was a Ca deficiency in these soils. Again, this is a soil
fertility/plant nutrition question rather than one of soil structure, but
the answer is 'no' - we occasionally see some early season blossom end rot
but it is not problem. He also mentioned checking the numbers again to make
sure I had them right. Yes indeed they are. The soils throughout the
western Sacramento Valley, I am told, are derived from marine deposits and
Ca:Mg ratios are generally less than 1. Moreover the ground and surface
waters used for irrigation have 2-3 times more dissolved Mg than Ca.
Farmers do add gypsum if they have a water infiltration problem, but as I
said, we certainly don't have one of those in the organic system.
Based upon the research that has already been done I'm not so sure that it
would be worth doing more studies in which Ca:Mg ratios are adjusted and
yields measured. It seems enough have been done. Perhaps research focused
just on soils with extremely low Ca:Mg ratios or on the reclamation of land
with poor structure would be worthwhile. And as it stands now, I see little
validity in the broad claims made by some consultants that the Ca:Mg ratio
of an agricultural soil should be 6.5 to 1, even as a general rule.
I am still interested in how this philosophical division between university
and commercial laboratories occurred. It appears to have begun over a half
century ago and it is amazing to me that it still exists. I am also still
eager to hear from other "happy customers" about their own success stories
from adding Ca (or unhappy customers) or from the consultants who recommend
this practice.
References cited
Bear, F. E. and S. J. Toth. 1948. Influence of calcium on availability of
other soil cations. Soil Sci. 65: 69-74.
Eckert, D. J. and E. O. McLean. 1981. Basic cation saturation ratios as a
basis for fertilizing and liming agronomic crops: I. Growth chamber studies.
Agron. J. 73: 795-799.
Liebhardt, W. C. 1981. The basic cation saturation ratio concept and lime
and potassium recommendations on Delaware's Coastal Plain soils. Soil Sci.
Soc. Am. J. 45: 544-549.
Reid, W. S. 1996. Influence of lime and calcium:magnesium ratio on alfalfa
and birdsfoot trefoil yields. Commun. Soil Sci. Plant Anal. 27: 1885-1900.
M. Sean Clark
Research Manager
Sustainable Agriculture Farming Systems Project
Department of Agronomy and Range Science
University of California
Davis, CA 95616
msclark@ucdavis.edu
TEL:(916) 752-2023
FAX:(916) 752-4361
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