Sean,
You raise a subject that has interested me for quite some time, as I, too have
often come across famers, salespeople and consultants who swear by Albrecht's
theories of cation balance. Unfortunately, none of the people I have asked has
been able (or willing) to provide any scientific basis or even replicated,
reliable data to support their contentions. I have been told that they have
"happy customers" not data. None of the farmers I have talked to have even tried
replicated strips to test the high - Calcium system effects, so they might have
been happy without it, too.
Certainly there is truth to the idea that Ca plays a critical role in
soil flocculation and plant (and animal) nutrition. The cation exchange complex
in mosat soils is dominated by Calcium ions (at least among the non-acid
cations). If the ratio of divalent to monovalent ions gets unusually low, soil
structure, permeability, and infiltration certainly suffer. While sodium is most
commonly to blame, there are documented reports of excessive potassium
applications having similar, but less dramatic effects. The effect of excessive
Magnesium and Potassium on Calcium uptake by plants is also well-documented, and
to be expected from charge balance considerations, among others. Actual Ca
deficiency is quite rare, and occurs almost exclusively on very acid soils where
it is difficult to distinguish from Aluminum toxicity. In solutions that are
extremely low in Ca, other metal ions (such as Mg) actually become toxic to
plant roots, for the Ca is needed to maintain cell membrane stability. Sean, if I
recall, your rotations include processing tomato, a plant that is very
susceptible to low Ca (which combined with uneven water) can cause blossum
end-rot. Has this ever occured on your plots?
The calcium content of animal forages is also quite important to animal
health. Grass tetany is an extreme case, sometimes associated with excessive
potassium and reduced magnesium and calcium intake. likewise, earthworms have a
definite requirement for Calcium in their environment, the amount depending on
the species. Calcium probably also can enhance general heterotrophic microbial
decomposition, as well as certain specific microbial species (some Rhizobia and
nitrifiers come to mind). However, in most studies the effects of Calcium and pH
are confounded. Lab and field evidence would indicate that pH is the overriding
factor.
However, I am aware that some consultants recommend applying calcium even
when pH is above 7.0. In humid regions this is generally not good advice, as
calcium in the form of limestone would result in too high a pH and thus
micronutrient deficiencies and other problems. However, in humid regions where pH
has been long maintained with dolomitic limestone (about 35% Mg), the ratio of
Mg to Ca can become an issue of concern. Magesnium has considerably less
flocculating ability than does Calcium, so I would recommend calcitic limestone
in most cases, unless available Mg by soil test is below "medium".
Low Magnesium is a problem more commonly than high. For example, Magnesium
saturation should general exceed that of potassium by a comfortable margin (say
2.5:1 or 3:1 or higher). If the ratio gets close to 1:1, or certainly if there
is more exchangeable K than Mg, deficiencies of Mg are quite likely in many
plants. This rarely happens in nature (except in some humid tropical soils), but
can result from heavy K fertilizer (or even poultry manure) application on some
soils.
Except for those which evolved on serpentine-derived soils, most plants are
adapted to a considerable predominace of exchangeable Ca over Mg and other
non-acid cations. To a large degree, plant roots can selectively take up what
they need, as evidenced by internal plant composition which can difer greatly
from the composition of the soil solution. However, extremely out of balance
soils can certainly affect plant uptake. I have seen no evidence that there is
any problem with ratios are disparate as 3:1 or 10:1 (Ca : Mg) , but clearly the
1:1 or lower that you report could be a problem. So the upshot is, check those Ca
and Mg saturation numbers again. Also, check the plant leaf tissue. Is the Ca
level unusally low? If there really are about equal moles of charge from the two
cations, yes, some gypsum might be in order (in both organic and conventional
systems). But that is treating the symptom. I'd want to know where all that Mg is
(or was) coming from. Magnesium uptake by corn and other grasses (not woody
trees, or tomato leaves, though) is not too different from that of Calcium, so
depletion rates are unlikely to explain it unless you have been removing all the
tomato vines for years (the leaves and stems may be 5 to 10 times as high in Ca
as in Mg, but the fruits have little of either Ca or Mg --but are vey high in K).
Are your soils derived from unusually Mg-rich parent materials?
I am sorry this "essay" has been so rambling. I wish I had time to look up
all the refernces for you. Many of the above considerations are discussed in
11th edition (and will be more so in the up-coming 12th edition) of The Nature
and Properties of Soils (by Nyle Brady and myself). Do let us know what you find
out on your soil and tissue analyses. (Oh yes, if you do apply gypsum, for all
our sakes, can you please split the plots or try a side experiment so we can get
some data on this!?)
Good luck,
Ray Weil
Sean Clark wrote:
> Soil Saneters:
>
> I am seeking some common ground and understanding on an issue which seems to
> be of extreme importance to many organic farmers and consultants but given
> little attention by academic scientists - that is soil cation balancing and
> the importance of calcium (Ca) in soil structure.
>
> Time and again, when speaking with organic farmers and the consultants who
> serve them, I find the importance of cation balancing and soil Ca come to
> the center of the conversation. In lay terms, the basic idea is that
> inadequate exchangeable Ca results in poor soil structure, characterized by
> "tightness" because the amount of pore space for air is less than optimal.
> Consequently, root health is compromised and nutrient availability and
> uptake reduced. A general rule often given is that the ratio of Ca to
> magnesium (Mg) should be about 5-7 to 1. If it is less - you need to add Ca.
>
> As the research manager of a long-term study/comparison of organic,
> low-input, and conventional farming systems at the Univ. of California at
> Davis, I am sometimes criticized by these folks for giving inadequate
> attention to this issue. In this study, all of the farming systems are
> managed according to "best farmer management" strategies - which are
> determined by a group of academic and Extension researchers, Extension farm
> advisors, and farmers. Admittedly, we have not made or altered any
> management practices in this study based on soil Ca:Mg ratios.
> Consequently, some organic farmers and consultants argue that the organic
> system in this study is being shortchanged because we have not given the
> soil Ca:Mg ratio proper attention.
>
> When I ask where I can get more information on this matter I am usually
> referred to William Albrecht and his Papers. He published a number of
> studies during the 1920-1940s in the J. Amer. Soc. Agron. but I have found
> that his name now seems to be reserved for the pages of Acres USA (not to
> diminish Acres USA). My point is that I find no recognition or
> ackowledgement of him or his work in basic or advanced textbooks on soil
> science and fertility management or among research scientists - even among
> those who are doing research on organic and low-input agriculture. It seems
> that Albrecht is to many in the organic movement what Stinner is to the
> Biodynamic movement. I see some people adhere to his "Papers" with almost
> religious conviction.
>
> Getting back to my problem: The Ca:Mg ratios of the soils at this study site
> are nowhere near 5-7:1. In fact, they are less than 1:1. The Ca:Mg ratio
> in the organic system in this study is significantly (statistically) higher
> than that of the conventional system due to the Ca in the composted and aged
> manures that have been added over the years, but in absolute terms the
> difference is still quite small. There is a clear difference, however, in
> water infiltration rates between the organic and conventional systems.
> Rates are much greater in the organic system (which we presume is due
> largely to the higher soil organic matter levels in this system).
> Therefore, if any of the farming systems in this study is in need of
> management to remedy a soil structural problem it would be the conventional
> system. And, indeed, the group has discussed applying gypsum to improve
> infiltration rates in the conventional system.
>
> However, the claims go beyond simply improving soil structure to enhance
> root growth and plant health. I am also told that the nitrogen (N)-use
> efficiency of the organic system would improve and that disease severity
> would decline with an increase the Ca:Mg ratio. The latter doesn't
> particularly interest me right now because diseases have not been a serious
> yield-limiting factor in any of the farming systems. But, the potential to
> improve N management in the organic system does. As many studies comparing
> organic to conventional systems have found, the release of mineral N from
> organic amendments and soil organic matter and uptake by the crop are not
> always predictable. Hence, we generally apply considerably more N to
> 'nitrophilic' crops in the organic system to compensate for unpredictable N
> mineralization and make up for that taken up by soil microbes or weeds. But
> losses from the organic system (due to leaching, denitrification, and
> volatilization) are not any greater in the organic compared to the
> conventional system. Therefore I do not see how the addition of Ca would
> reduce the amount of N which needs to be added - even over a long term.
>
> Ouestions:
>
> Are Albrecht's views accepted by "mainstream" soil scientists or are his
> ideas considered fringe? Do any university laboratories adhere to any of
> his concepts? Can anyone direct me to studies on Ca:Mg ratios and cation
> balancing (I have found very few)? Also, do any growers on the list have
> personal experiences with using soil Ca:Mg ratios in fertility or disease
> management ?
>
> Thanks in advance,
>
> Sean
>
> 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
>
> To Unsubscribe: Email majordomo@ces.ncsu.edu with "unsubscribe sanet-mg".
> To Subscribe to Digest: Email majordomo@ces.ncsu.edu with the command
> "subscribe sanet-mg-digest".
--------------2E60EFBED4E2C2E3903B2F33
Content-Type: text/x-vcard; charset=us-ascii; name="vcard.vcf"
Content-Transfer-Encoding: 7bit
Content-Description: Card for Ray R. Weil
Content-Disposition: attachment; filename="vcard.vcf"
begin: vcard
fn: Ray R. Weil
n: Weil;Ray R.
org: University of Maryland, College Park, MD 20742
adr: Dept. of Natural Resource Sciences & L.A.;;1103b H.J. Patterson Hall;College Park;Maryland;20742;USA
email;internet: rw17@umail.umd.edu
title: Professor of Soil Science
tel;work: 301 405 1314
tel;fax: 301 314 9041
x-mozilla-cpt: ;0
x-mozilla-html: FALSE
version: 2.1
end: vcard
--------------2E60EFBED4E2C2E3903B2F33--
To Unsubscribe: Email majordomo@ces.ncsu.edu with "unsubscribe sanet-mg".
To Subscribe to Digest: Email majordomo@ces.ncsu.edu with the command
"subscribe sanet-mg-digest".